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Q&A Can I make an AC inductor (reactor) rated 75mH 40A from a 3-phase induction motor?

An induction motor with its shaft held still will mostly look like an inductor with a series resistance electrically. However, there will be some issues: It will be difficult to guess the inducta...

posted 6mo ago by Olin Lathrop‭ · edited 6mo ago by Olin Lathrop‭

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#2: Post edited by

Olin Lathrop‭ · 2023-11-06T12:51:44Z (6 months ago)

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An induction motor with its shaft held still will mostly look like an inductor with a series resistance electrically. However, there will be some issues:<ol>
<li>It will be difficult to guess the inductance from the motor datasheet.
<li>There will probably be higher effective series resistance than for a deliberate inductor.
<li>It will be more lossy. The rotor is now just the secondary of a transformer that is effectively shorted. It doesn't add any DC inductance, but will dissipate power when AC is applied.
<li>The upper frequency limit where this thing still largely acts like an inductor will probably be quite low. If you only care about behavior at 50 Hz, then this probably won't matter.
</ol>
~~All around, this does not sound like a great idea. By the time you get a motor big enough to act like the inductor you want, you will have probably paid for a proper inductor.~~

An induction motor with its shaft held still will mostly look like an inductor with a series resistance electrically. However, there will be some issues:<ol>
<li>It will be difficult to guess the inductance from the motor datasheet.
<li>There will probably be higher effective series resistance than for a deliberate inductor.
<li>It will be more lossy. The rotor is now just the secondary of a transformer that is effectively shorted. It doesn't add any DC inductance, but will dissipate power when AC is applied.
<li>The upper frequency limit where this thing still largely acts like an inductor will probably be quite low. If you only care about behavior at 50 Hz, then this probably won't matter.
</ol>
All around, this does not sound like a great idea. By the time you get a motor big enough to act like the inductor you want, you will have probably paid for a proper inductor.
<blockquote>Price and availability</blockquote>
Since you are very price-sensitive and this seems to be a one-off, look into getting a core and winding your own inductor.

#1: Initial revision by

Olin Lathrop‭ · 2023-11-05T20:23:55Z (6 months ago)

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An induction motor with its shaft held still will mostly look like an inductor with a series resistance electrically.  However, there will be some issues:<ol>

<li>It will be difficult to guess the inductance from the motor datasheet.

<li>There will probably be higher effective series resistance than for a deliberate inductor.

<li>It will be more lossy.  The rotor is now just the secondary of a transformer that is effectively shorted.  It doesn't add any DC inductance, but will dissipate power when AC is applied.

<li>The upper frequency limit where this thing still largely acts like an inductor will probably be quite low.  If you only care about behavior at 50 Hz, then this probably won't matter.

</ol>

All around, this does not sound like a great idea.  By the time you get a motor big enough to act like the inductor you want, you will have probably paid for a proper inductor.

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