Post History

66%

+2 −0

Q&A High power LC circuit with programmable resonant frequency

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (1-5000 Hz). The inductor coil is a...

1 answer · posted 1y ago by dcsuka‭ · edited 1y ago by dcsuka‭

Question LC-network capacitor power inductor AC-power

#15: Post edited by

dcsuka‭ · 2023-06-28T16:46:29Z (over 1 year ago)

Copy Link

Raw

Markdown

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (1-5000 Hz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high-current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uF power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors decreasing from 6.0 uF in powers of 2 all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the switching leads of every pair connected and switched simultaneously by a logic-level MOSFET, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge (MOSFETs passively cooled at 10 C/W).
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?
EDIT:
I understand that my design idea will certainly not generate perfect resonance at all frequencies, with a noteworthy high-impedance region below about 200 Hz. Using the additional capacitor bank bypass relay (just the coil without capacitors) I could significantly improve current output at that region (see calculations). Some imperfection is definitely acceptable.
My end goal is to explore the effects of electromagnetic frequencies on biological and crystalline systems, and I would like the final coil current to be at least 20 Amps RMS at any frequency, ideally higher to maximize the effects. There should be as much frequency uniformity in current output as possible (under $500 budget for this) to avoid biasing results. I apologize if that is too vague, perhaps I need to reflect more on my design goals.
Since the magnetic field generated is proportional to current, I figured that using capacitors for resonance would allow the maximum current to flow in a more frequency-uniform fashion, especially at the higher end of the 1-5000 Hz region. I suppose I could use a class D audio amp alone with no capacitors, but the current and magnetic field would be lower at these higher frequencies. A 3 kW class D audio amp is likely cheaper than an H bridge + 3 kW DC power supply, so it is certainly an option if used with the variable capacitor bank. Would you recommend this?
Calculations:
Assuming an inductance of 6 mH and maximum capacitance of 66 uF (minimum resonant frequency 252.92 Hz), the frequency at which the purely inductive reactance (capacitor bank bypassed) matches the net reactance of the inductor in series with 66 uF is 178.837 Hz.
```
XL = XC - XL
w*L = 1 / (w*C) - w*L
2*w*L*w*C = 1
w = sqrt(1/2LC)
2*pi*f = sqrt(1/2LC)
f = 178.837 Hz
```
Assuming that I use enough smaller capacitors such that this is the highest reactance frequency, the maximum impedance is:
```
Xmax = 2 * pi * 178.837 Hz * L = 6.742
Rohmic = 3.3 ohms
Zmax = sqrt(Xmax ^ 2 + Rohmic ^ 2) = 7.506 ohms
I need an RMS power of:
P = I^2 * Z
P = 20^2 * 7.506 = 3002.52 W
and an RMS voltage of:
V = IZ = 150.12 Volts
```
At 10 mH, redoing these calculations we would need 3723.38 W max, so 4000 W RMS is probably a safe power to go with to get at least 20 A at any frequency in the range.

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (1-5000 Hz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high-current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uF power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors decreasing from 6.0 uF in powers of 2 all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the switching leads of every pair connected and switched simultaneously by a logic-level MOSFET, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge (MOSFETs passively cooled at 10 C/W).
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?
EDIT:
I understand that my design idea will certainly not generate perfect resonance at all frequencies, with a noteworthy high-impedance region below about 200 Hz. Using the additional capacitor bank bypass relay (just the coil without capacitors) I could significantly improve current output at that region (see calculations). Some imperfection is definitely acceptable.
My end goal is to explore the effects of electromagnetic frequencies on biological and crystalline systems, and I would like the final coil current to be 20 Amps RMS at any frequency between 1-5000 Hz. To be able to achieve this either requires an enormous amount of voltage/power at 5000 Hz or some form of adjustable capacitance. I apologize if that is too vague, perhaps I need to reflect more on my design goals.
Since the magnetic field generated is proportional to current, I figured that using capacitors for resonance would allow the maximum current to flow in a more frequency-uniform fashion, especially at the higher end of the 1-5000 Hz region. I suppose I could use a class D audio amp alone with no capacitors, but the current and magnetic field would be lower at these higher frequencies. A 3 kW class D audio amp is likely cheaper than an H bridge + 3 kW DC power supply, so it is certainly an option if used with the variable capacitor bank. Would you recommend this?
Calculations:
Assuming an inductance of 6 mH and maximum capacitance of 66 uF (minimum resonant frequency 252.92 Hz), the frequency at which the purely inductive reactance (capacitor bank bypassed) matches the net reactance of the inductor in series with 66 uF is 178.837 Hz.
```
XL = XC - XL
w*L = 1 / (w*C) - w*L
2*w*L*w*C = 1
w = sqrt(1/2LC)
2*pi*f = sqrt(1/2LC)
f = 178.837 Hz
```
Assuming that I use enough smaller capacitors such that this is the highest reactance frequency, the maximum impedance is:
```
Xmax = 2 * pi * 178.837 Hz * L = 6.742
Rohmic = 3.3 ohms
Zmax = sqrt(Xmax ^ 2 + Rohmic ^ 2) = 7.506 ohms
I need an RMS power of:
P = I^2 * Z
P = 20^2 * 7.506 = 3002.52 W
and an RMS voltage of:
V = IZ = 150.12 Volts
```
At 10 mH, redoing these calculations we would need 3723.38 W max, so 4000 W RMS is probably a safe power to go with to get at least 20 A at any frequency in the range.

#14: Post edited by

dcsuka‭ · 2023-06-28T01:23:18Z (over 1 year ago)

Copy Link

Raw

Markdown

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (1-5000 Hz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high-current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uF power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors decreasing from 6.0 uF in powers of 2 all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the switching leads of every pair connected and switched simultaneously by a logic-level MOSFET, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge (MOSFETs passively cooled at 10 C/W).
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?
EDIT:
I understand that my design idea will certainly not generate perfect resonance at all frequencies, with a noteworthy high-impedance region below about 200 Hz. Using the additional capacitor bank bypass relay (just the coil without capacitors) I could significantly improve current output at that region (see calculations). Some imperfection is definitely acceptable.
My end goal is to explore the effects of electromagnetic frequencies on biological and crystalline systems, and I would like the final coil current to be at least 20 Amps RMS at any frequency, ideally higher to maximize the effects. There should be as much frequency uniformity in current output as possible (under $500 budget for this) to avoid biasing results. I apologize if that is too vague, perhaps I need to reflect more on my design goals.
Since the magnetic field generated is proportional to current, I figured that using capacitors for resonance would allow the maximum current to flow in a more frequency-uniform fashion, especially at the higher end of the 1-5000 Hz region. I suppose I could use a class D audio amp alone with no capacitors, but the current and magnetic field would be lower at these higher frequencies. A 3 kW class D audio amp is likely cheaper than an H bridge + 3 kW DC power supply, so it is certainly an option if used with the variable capacitor bank. Would you recommend this?
Calculations:
Assuming an inductance of 6 mH, maximum capacitance of 66 uF, minimum resonant frequency 252.92 Hz, the frequency at which the purely inductive reactance (capacitor bank bypassed) matches the net reactance of the inductor in series with 66 uF is 178.837 Hz.
```
XL = XC - XL
w*L = 1 / (w*C) - w*L
2*w*L*w*C = 1
w = sqrt(1/2LC)
2*pi*f = sqrt(1/2LC)
f = 178.837 Hz
```
Assuming that I use enough smaller capacitors such that this is the highest reactance frequency, the maximum impedance is:
```
Xmax = 2 * pi * 178.837 Hz * L = 6.742
Rohmic = 3.3 ohms
Zmax = sqrt(Xmax ^ 2 + Rohmic ^ 2) = 7.506 ohms
I need an RMS power of:
P = I^2 * Z
P = 20^2 * 7.506 = 3002.52 W
and an RMS voltage of:
V = IZ = 150.12 Volts
```
~~At 10 mH, redoing these calculations we would need 3723.38 W max, so 4000 W RMS is probably a safe power to go with to get at least 20 A at any frequency in that range.~~

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (1-5000 Hz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high-current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uF power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors decreasing from 6.0 uF in powers of 2 all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the switching leads of every pair connected and switched simultaneously by a logic-level MOSFET, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge (MOSFETs passively cooled at 10 C/W).
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?
EDIT:
I understand that my design idea will certainly not generate perfect resonance at all frequencies, with a noteworthy high-impedance region below about 200 Hz. Using the additional capacitor bank bypass relay (just the coil without capacitors) I could significantly improve current output at that region (see calculations). Some imperfection is definitely acceptable.
My end goal is to explore the effects of electromagnetic frequencies on biological and crystalline systems, and I would like the final coil current to be at least 20 Amps RMS at any frequency, ideally higher to maximize the effects. There should be as much frequency uniformity in current output as possible (under $500 budget for this) to avoid biasing results. I apologize if that is too vague, perhaps I need to reflect more on my design goals.
Since the magnetic field generated is proportional to current, I figured that using capacitors for resonance would allow the maximum current to flow in a more frequency-uniform fashion, especially at the higher end of the 1-5000 Hz region. I suppose I could use a class D audio amp alone with no capacitors, but the current and magnetic field would be lower at these higher frequencies. A 3 kW class D audio amp is likely cheaper than an H bridge + 3 kW DC power supply, so it is certainly an option if used with the variable capacitor bank. Would you recommend this?
Calculations:
Assuming an inductance of 6 mH and maximum capacitance of 66 uF (minimum resonant frequency 252.92 Hz), the frequency at which the purely inductive reactance (capacitor bank bypassed) matches the net reactance of the inductor in series with 66 uF is 178.837 Hz.
```
XL = XC - XL
w*L = 1 / (w*C) - w*L
2*w*L*w*C = 1
w = sqrt(1/2LC)
2*pi*f = sqrt(1/2LC)
f = 178.837 Hz
```
Assuming that I use enough smaller capacitors such that this is the highest reactance frequency, the maximum impedance is:
```
Xmax = 2 * pi * 178.837 Hz * L = 6.742
Rohmic = 3.3 ohms
Zmax = sqrt(Xmax ^ 2 + Rohmic ^ 2) = 7.506 ohms
I need an RMS power of:
P = I^2 * Z
P = 20^2 * 7.506 = 3002.52 W
and an RMS voltage of:
V = IZ = 150.12 Volts
```
At 10 mH, redoing these calculations we would need 3723.38 W max, so 4000 W RMS is probably a safe power to go with to get at least 20 A at any frequency in the range.

#13: Post edited by

dcsuka‭ · 2023-06-28T01:20:49Z (over 1 year ago)

Copy Link

Raw

Markdown

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (1-5000 Hz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high-current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uF power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors decreasing from 6.0 uF in powers of 2 all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the switching leads of every pair connected and switched simultaneously by a logic-level MOSFET, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge (MOSFETs passively cooled at 10 C/W).
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?
EDIT:
I understand that my design idea will certainly not generate perfect resonance at all frequencies, with a noteworthy high-impedance region below about 200 Hz. Using the additional capacitor bank bypass relay (just the coil without capacitors) I could basically split that region in half with highest impedance at about 100 Hz. Some imperfection is definitely acceptable.
My end goal is to explore the effects of electromagnetic frequencies on biological and crystalline systems, and I would like the final coil current to be at least 20 Amps RMS, ideally higher to maximize the effects. There should be as much frequency uniformity in power output as possible (under $500 budget for this) to avoid biasing results. I apologize if that is too vague, perhaps I need to reflect more on my design goals.
Since the magnetic field generated is proportional to current, I figured that using capacitors for resonance would allow the maximum current to flow in a more frequency-uniform fashion, especially at the higher end of the 1-5000 Hz region. I suppose I could use a class D audio amp alone with no capacitors, but the current and magnetic field would be lower at these higher frequencies. A 3-6 kW class D audio amp is likely cheaper than an H bridge + 3-6 kW DC power supply, so it is certainly an option if used with the variable capacitor bank. Would you recommend this?

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (1-5000 Hz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high-current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uF power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors decreasing from 6.0 uF in powers of 2 all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the switching leads of every pair connected and switched simultaneously by a logic-level MOSFET, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge (MOSFETs passively cooled at 10 C/W).
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?
EDIT:
I understand that my design idea will certainly not generate perfect resonance at all frequencies, with a noteworthy high-impedance region below about 200 Hz. Using the additional capacitor bank bypass relay (just the coil without capacitors) I could significantly improve current output at that region (see calculations). Some imperfection is definitely acceptable.
My end goal is to explore the effects of electromagnetic frequencies on biological and crystalline systems, and I would like the final coil current to be at least 20 Amps RMS at any frequency, ideally higher to maximize the effects. There should be as much frequency uniformity in current output as possible (under $500 budget for this) to avoid biasing results. I apologize if that is too vague, perhaps I need to reflect more on my design goals.
Since the magnetic field generated is proportional to current, I figured that using capacitors for resonance would allow the maximum current to flow in a more frequency-uniform fashion, especially at the higher end of the 1-5000 Hz region. I suppose I could use a class D audio amp alone with no capacitors, but the current and magnetic field would be lower at these higher frequencies. A 3 kW class D audio amp is likely cheaper than an H bridge + 3 kW DC power supply, so it is certainly an option if used with the variable capacitor bank. Would you recommend this?
Calculations:
Assuming an inductance of 6 mH, maximum capacitance of 66 uF, minimum resonant frequency 252.92 Hz, the frequency at which the purely inductive reactance (capacitor bank bypassed) matches the net reactance of the inductor in series with 66 uF is 178.837 Hz.
```
XL = XC - XL
w*L = 1 / (w*C) - w*L
2*w*L*w*C = 1
w = sqrt(1/2LC)
2*pi*f = sqrt(1/2LC)
f = 178.837 Hz
```
Assuming that I use enough smaller capacitors such that this is the highest reactance frequency, the maximum impedance is:
```
Xmax = 2 * pi * 178.837 Hz * L = 6.742
Rohmic = 3.3 ohms
Zmax = sqrt(Xmax ^ 2 + Rohmic ^ 2) = 7.506 ohms
I need an RMS power of:
P = I^2 * Z
P = 20^2 * 7.506 = 3002.52 W
and an RMS voltage of:
V = IZ = 150.12 Volts
```
At 10 mH, redoing these calculations we would need 3723.38 W max, so 4000 W RMS is probably a safe power to go with to get at least 20 A at any frequency in that range.

#12: Post edited by

dcsuka‭ · 2023-06-28T00:22:55Z (over 1 year ago)

Copy Link

Raw

Markdown

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (1-5000 Hz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high-current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uF power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors decreasing from 6.0 uF in powers of 2 all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the switching leads of every pair connected and switched simultaneously by a logic-level MOSFET, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge (MOSFETs passively cooled at 10 C/W).
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?
EDIT:
I understand that my design idea will certainly not generate perfect resonance at all frequencies, with a noteworthy high-impedance region below about 200 Hz. Using the additional capacitor bank bypass relay (just the coil without capacitors) I could basically split that region in half with high impedance at about 100 Hz. Some imperfection is definitely acceptable.
My end goal is to explore the effects of electromagnetic frequencies on biological and crystalline systems, and I would like the final coil current to be at least 20 Amps RMS, ideally higher to maximize the effects. There should be as much frequency uniformity in power output as possible (under $500 budget for this) to avoid biasing results. I apologize if that is too vague, perhaps I need to reflect more on my design goals.
Since the magnetic field generated is proportional to current, I figured that using capacitors for resonance would allow the maximum current to flow in a more frequency-uniform fashion, especially at the higher end of the 1-5000 Hz region. I suppose I could use a class D audio amp alone with no capacitors, but the current and magnetic field would be lower at these higher frequencies. A 3-6 kW class D audio amp is likely cheaper than an H bridge + 3-6 kW DC power supply, so it is certainly an option if used with the variable capacitor bank. Would you recommend this?

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (1-5000 Hz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high-current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uF power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors decreasing from 6.0 uF in powers of 2 all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the switching leads of every pair connected and switched simultaneously by a logic-level MOSFET, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge (MOSFETs passively cooled at 10 C/W).
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?
EDIT:
I understand that my design idea will certainly not generate perfect resonance at all frequencies, with a noteworthy high-impedance region below about 200 Hz. Using the additional capacitor bank bypass relay (just the coil without capacitors) I could basically split that region in half with highest impedance at about 100 Hz. Some imperfection is definitely acceptable.
My end goal is to explore the effects of electromagnetic frequencies on biological and crystalline systems, and I would like the final coil current to be at least 20 Amps RMS, ideally higher to maximize the effects. There should be as much frequency uniformity in power output as possible (under $500 budget for this) to avoid biasing results. I apologize if that is too vague, perhaps I need to reflect more on my design goals.
Since the magnetic field generated is proportional to current, I figured that using capacitors for resonance would allow the maximum current to flow in a more frequency-uniform fashion, especially at the higher end of the 1-5000 Hz region. I suppose I could use a class D audio amp alone with no capacitors, but the current and magnetic field would be lower at these higher frequencies. A 3-6 kW class D audio amp is likely cheaper than an H bridge + 3-6 kW DC power supply, so it is certainly an option if used with the variable capacitor bank. Would you recommend this?

#11: Post edited by

dcsuka‭ · 2023-06-28T00:20:53Z (over 1 year ago)

Copy Link

Raw

Markdown

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (1-5000 Hz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high-current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uF power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors decreasing from 6.0 uF in powers of 2 all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the switching leads of every pair connected and switched simultaneously by a logic-level MOSFET, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge (MOSFETs passively cooled at 10 C/W).
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?
EDIT:
I understand that my design idea will certainly not generate perfect resonance at all frequencies, with a noteworthy high-impedance region below about 200 Hz, so using the additional capacitor bank bypass relay I could basically split that region in half with high impedance at about 100 Hz. Some imperfection is definitely necessary.
My end goal is to explore the effects of electromagnetic frequencies on biological and crystalline systems, and I would like the final output power to be between 3 and 6 kW, ideally as high as possible to maximize the effects. There should be as much frequency uniformity in power output as possible (in a reasonable budget) to avoid biasing results. I apologize if that is too vague, perhaps I need to reflect more on my design goals.
Since the magnetic field generated is proportional to current, I figured that using capacitors for resonance would allow the maximum current to flow in a more frequency-uniform fashion, especially at the higher end of the 1-5000 Hz region. I suppose I could use a class D audio amp alone with no capacitors, but the current and magnetic field would be lower at these higher frequencies. A 3-6 kW class D audio amp is likely cheaper than an H bridge + 3-6 kW DC power supply, so it is certainly an option if used with the variable capacitor bank. Would you recommend this?

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (1-5000 Hz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high-current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uF power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors decreasing from 6.0 uF in powers of 2 all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the switching leads of every pair connected and switched simultaneously by a logic-level MOSFET, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge (MOSFETs passively cooled at 10 C/W).
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?
EDIT:
I understand that my design idea will certainly not generate perfect resonance at all frequencies, with a noteworthy high-impedance region below about 200 Hz. Using the additional capacitor bank bypass relay (just the coil without capacitors) I could basically split that region in half with high impedance at about 100 Hz. Some imperfection is definitely acceptable.
My end goal is to explore the effects of electromagnetic frequencies on biological and crystalline systems, and I would like the final coil current to be at least 20 Amps RMS, ideally higher to maximize the effects. There should be as much frequency uniformity in power output as possible (under $500 budget for this) to avoid biasing results. I apologize if that is too vague, perhaps I need to reflect more on my design goals.
Since the magnetic field generated is proportional to current, I figured that using capacitors for resonance would allow the maximum current to flow in a more frequency-uniform fashion, especially at the higher end of the 1-5000 Hz region. I suppose I could use a class D audio amp alone with no capacitors, but the current and magnetic field would be lower at these higher frequencies. A 3-6 kW class D audio amp is likely cheaper than an H bridge + 3-6 kW DC power supply, so it is certainly an option if used with the variable capacitor bank. Would you recommend this?

#10: Post edited by

dcsuka‭ · 2023-06-28T00:13:13Z (over 1 year ago)

Copy Link

Raw

Markdown

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (1-5000 Hz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high-current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uF power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors decreasing from 6.0 uF in powers of 2 all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the switching leads of every pair connected and switched simultaneously by a logic-level MOSFET, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge (MOSFETs passively cooled at 10 C/W).
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?
EDIT:
I understand that my design idea will certainly not generate perfect resonance at all frequencies, with a noteworthy high-impedance region below about 200 Hz, so using the additional capacitor bank bypass relay I could basically split that region in half with high impedance at about 100 Hz. Some imperfection is definitely necessary.
My end goal is to explore the effects of electromagnetic frequencies on biological and crystalline systems, and I would like the final output power to be between 3 and 6 kW, ideally as high as possible to maximize the effects. There should be as much frequency uniformity in power output as possible in a reasonable budget to avoid biasing results. I apologize if that is too vague, perhaps I need to reflect more on my design goals.
Since the magnetic field generated is proportional to current, I figured that using capacitors for resonance would allow the maximum current to flow in a more frequency-uniform fashion, especially at the higher end of the 1-5000 Hz region. I suppose I could use a class D audio amp alone with no capacitors, but the current and magnetic field would be lower at these higher frequencies. A class D audio amp is likely cheaper than an H bridge + 3 kW DC power supply, so it is certainly an option. Would you recommend the class D audio amp, possibly coupled with my switchable capacitor bank idea?

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (1-5000 Hz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high-current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uF power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors decreasing from 6.0 uF in powers of 2 all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the switching leads of every pair connected and switched simultaneously by a logic-level MOSFET, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge (MOSFETs passively cooled at 10 C/W).
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?
EDIT:
I understand that my design idea will certainly not generate perfect resonance at all frequencies, with a noteworthy high-impedance region below about 200 Hz, so using the additional capacitor bank bypass relay I could basically split that region in half with high impedance at about 100 Hz. Some imperfection is definitely necessary.
My end goal is to explore the effects of electromagnetic frequencies on biological and crystalline systems, and I would like the final output power to be between 3 and 6 kW, ideally as high as possible to maximize the effects. There should be as much frequency uniformity in power output as possible (in a reasonable budget) to avoid biasing results. I apologize if that is too vague, perhaps I need to reflect more on my design goals.
Since the magnetic field generated is proportional to current, I figured that using capacitors for resonance would allow the maximum current to flow in a more frequency-uniform fashion, especially at the higher end of the 1-5000 Hz region. I suppose I could use a class D audio amp alone with no capacitors, but the current and magnetic field would be lower at these higher frequencies. A 3-6 kW class D audio amp is likely cheaper than an H bridge + 3-6 kW DC power supply, so it is certainly an option if used with the variable capacitor bank. Would you recommend this?

#9: Post edited by

dcsuka‭ · 2023-06-28T00:06:24Z (over 1 year ago)

Copy Link

Raw

Markdown

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (1-5000 Hz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high-current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uF power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors decreasing from 6.0 uF in powers of 2 all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the switching leads of every pair connected and switched simultaneously by a logic-level MOSFET, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge (MOSFETs passively cooled at 10 C/W).
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (1-5000 Hz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high-current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uF power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors decreasing from 6.0 uF in powers of 2 all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the switching leads of every pair connected and switched simultaneously by a logic-level MOSFET, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge (MOSFETs passively cooled at 10 C/W).
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?
EDIT:
I understand that my design idea will certainly not generate perfect resonance at all frequencies, with a noteworthy high-impedance region below about 200 Hz, so using the additional capacitor bank bypass relay I could basically split that region in half with high impedance at about 100 Hz. Some imperfection is definitely necessary.
My end goal is to explore the effects of electromagnetic frequencies on biological and crystalline systems, and I would like the final output power to be between 3 and 6 kW, ideally as high as possible to maximize the effects. There should be as much frequency uniformity in power output as possible in a reasonable budget to avoid biasing results. I apologize if that is too vague, perhaps I need to reflect more on my design goals.
Since the magnetic field generated is proportional to current, I figured that using capacitors for resonance would allow the maximum current to flow in a more frequency-uniform fashion, especially at the higher end of the 1-5000 Hz region. I suppose I could use a class D audio amp alone with no capacitors, but the current and magnetic field would be lower at these higher frequencies. A class D audio amp is likely cheaper than an H bridge + 3 kW DC power supply, so it is certainly an option. Would you recommend the class D audio amp, possibly coupled with my switchable capacitor bank idea?

#8: Post edited by

dcsuka‭ · 2023-06-24T15:53:18Z (over 1 year ago)

Copy Link

Raw

Markdown

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (1-5000 Hz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high-current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uF power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors decreasing from 6.0 uF in powers of 2 all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the leads of every pair connected and switched simultaneously by a transistor, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge.
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (1-5000 Hz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high-current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uF power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors decreasing from 6.0 uF in powers of 2 all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the switching leads of every pair connected and switched simultaneously by a logic-level MOSFET, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge (MOSFETs passively cooled at 10 C/W).
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?

#7: Post edited by

dcsuka‭ · 2023-06-24T15:51:12Z (over 1 year ago)

Copy Link

Raw

Markdown

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (1-5000 Hz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
~~I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high current high-capacitance programmable variable capacitor.~~
I will have about ten [6.0 uF power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors decreasing from 6.0 uF in powers of 2 all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the leads of every pair connected and switched simultaneously by a transistor, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge.
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (1-5000 Hz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high-current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uF power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors decreasing from 6.0 uF in powers of 2 all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the leads of every pair connected and switched simultaneously by a transistor, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge.
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?

#6: Post edited by

dcsuka‭ · 2023-06-24T15:50:51Z (over 1 year ago)

Copy Link

Raw

Markdown

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (1-5000 Hz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uf power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors decreasing from 6.0 uF in powers of 2 all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the leads of every pair connected and switched simultaneously by a transistor, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge.
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (1-5000 Hz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uF power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors decreasing from 6.0 uF in powers of 2 all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the leads of every pair connected and switched simultaneously by a transistor, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge.
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?

#5: Post edited by

dcsuka‭ · 2023-06-24T15:49:55Z (over 1 year ago)

Copy Link

Raw

Markdown

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (1-5 Khz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uf power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors decreasing from 6.0 uF in powers of 2 all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the leads of every pair connected and switched simultaneously by a transistor, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge.
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (1-5000 Hz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uf power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors decreasing from 6.0 uF in powers of 2 all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the leads of every pair connected and switched simultaneously by a transistor, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge.
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?

#4: Post edited by

dcsuka‭ · 2023-06-24T15:49:33Z (over 1 year ago)

Copy Link

Raw

Markdown

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (0-5 Khz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uf power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the leads of every pair connected and switched simultaneously by a transistor, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge.
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (1-5 Khz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uf power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors decreasing from 6.0 uF in powers of 2 all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the leads of every pair connected and switched simultaneously by a transistor, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge.
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?

#3: Post edited by

dcsuka‭ · 2023-06-24T15:46:04Z (over 1 year ago)

Copy Link

Raw

Markdown

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly low audio range (0-5000 Khz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uf power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the leads of every pair connected and switched simultaneously by a transistor, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge.
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly audio range (0-5 Khz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uf power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the leads of every pair connected and switched simultaneously by a transistor, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge.
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?

#2: Post edited by

dcsuka‭ · 2023-06-23T22:04:02Z (over 1 year ago)

Copy Link

Raw

Markdown

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly low audio range (0-5000 Khz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 33 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uf power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the leads of every pair connected and switched simultaneously by a transistor, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge.
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly low audio range (0-5000 Khz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 30 amps assuming no net reactance.
I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high current high-capacitance programmable variable capacitor.
I will have about ten [6.0 uf power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the leads of every pair connected and switched simultaneously by a transistor, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge.
I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?

#1: Initial revision by

dcsuka‭ · 2023-06-23T21:59:01Z (over 1 year ago)

Copy Link

Raw

Markdown

High power LC circuit with programmable resonant frequency

I intend to build a high-power series LC resonant circuit for the purpose of generating strong magnetic fields at a wide range of frequencies, mostly low audio range (0-5000 Khz). The inductor coil is about 5-10 mH and 3.3 ohms of 15-gauge copper wire, so I will need about 60-80 uf maximum capacitance to achieve low impedance at the lowest frequencies in that range. The circuit will be driven by a power H-bridge at 100 Volts amplitude, so I calculate that the peak current will be at my target of 33 amps assuming no net reactance.

I wish to be able to sweep the frequency in an automated fashion, so I would like feedback on my design for a high current high-capacitance programmable variable capacitor.

I will have about ten [6.0 uf power capacitors](https://www.aliexpress.us/item/3256805362490310.html?spm=a2g0o.store_pc_groupList.8148356.4.16cf4349IemvIL&pdp_npi=3%40dis%21USD%21US%20%2412.96%21US%20%2412.32%21%21%21%21%21%402103228816875548942525230ef0fe%2112000033495487735%21sh%21US%210&gatewayAdapt=glo2usa) and a few lower capacitance capacitors all in parallel. My idea is to have a [high-current mechanical relay](https://www.mouser.com/ProductDetail/CUI-Devices/PR24-12V-900-1A?qs=T%252BzbugeAwjiyaDLvBGWPGw%3D%3D) on each side of each capacitor, with the leads of every pair connected and switched simultaneously by a transistor, which is controlled by the same MCU that controls the H-bridge. There will be an option to bypass the capacitor bank altogether with an extra relay for very low frequencies (<100 Hz). I will calibrate the design ahead of time to determine the lowest impedance capacitor combination for any given frequency. The relays have a contact current rating of 40 amps and the capacitors are rated at 50-70 amps RMS. I will have a few separate fans blowing air onto the coil, capacitor bank, and H-bridge.

I don't have much experience with power electronics, so I was wondering if any of you had design suggestions or can see some obvious pitfalls? Are there any already existing designs for high-power variable capacitors like this that I am not aware of?

LC-network capacitor power inductor AC-power

Communities

Post History