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That's a marketing blurb. Look at the real datasheet. I just checked a polyfuse datasheet, and see that there is usually only about a 2.5 to 3.0 ratio of trip current to hold current. That shoul...
Answer
#3: Post edited
by
Olin Lathrop
·
2021-09-29T18:52:13Z (about 3 years ago)
- That's a marketing blurb. Look at the real datasheet.
- I just checked a polyfuse datasheet, and see that there is usually only about a 2.5 to 3.0 ratio of trip current to hold current. That should be enough to keep the motor from overheating.
- Polyfuses work on heat. When cold, they have low resistance. Over-current heats them up, which makes the resistance go up. It then requires lower current to maintain the temperature that maintains the high resitance.
- The main downside of polyfuses is the relatively large series resistance. They may not be appropriate for your motor application for this reason.
An electronic fuse, as you seem to have, is a better choice. You can then control directly how much current for how long you want to allow. With a properly working electronic fuse, you can use a plain old melting link fuse as a backup, since it should never trip unless there is an outright failure in your electronics somewhere. A stuck motor won't blow the fuse since the electronic system already limits the current and/or shuts down the motor.
- That's a marketing blurb. Look at the real datasheet.
- I just checked a polyfuse datasheet, and see that there is usually only about a 2.5 to 3.0 ratio of trip current to hold current. That should be enough to keep the motor from overheating.
- Polyfuses work on heat. When cold, they have low resistance. Over-current heats them up, which makes the resistance go up. It then requires lower current to maintain the temperature that maintains the high resitance.
- The main downside of polyfuses is the relatively large series resistance. They may not be appropriate for your motor application for this reason.
- An electronic fuse, as you seem to have, is a better choice. You can then control directly how much current for how long you want to allow. With a properly working electronic fuse, you can use a plain old melting link fuse as a backup, since it should never trip unless there is an outright failure in your electronics somewhere. A stuck motor won't blow the fuse since the electronic system already limits the current and/or shuts down the motor.
- <hr>
- <blockquote>But if the motor has say 200mA running through it for hours at a time without completing any work (i.e. just sitting there and heating up), wouldn't that cause some heat damage to it?</blockquote>
- Not necessarily. Motor heating comes from I<sup>2</sup>R losses in the coils. We'll ignore heating of the bearings from friction for this case, since that goes to zero when the motor is stalled anyway.
- If we consider the coils resistance fixed, then electrical heating is proportional to the square of the current. Note that how fast the motor is turning has nothing to do with this.
- The reason we worry about a stalled motor overheating is because this assumes the motor is being driven with a fixed voltage. When the motor isn't turning, there is no back EMF opposing the driving voltage. All the driving voltage appears across the coil resistance. When the motor turns, the effective voltage across the coil resistance is less, so less power dissipated in that resistance.
- If you are controlling the current directly, then the back EMF doesn't matter for heating purposes. When the motor is stalled, it will automatically take less voltage to cause the current. Either way, though, the dissipation in the coil resistance is still proportional to the square of the current only.
- For some motors, the motor motion is also used for air cooling internally. In that case, a stalled motor is less able to get rid of heat, and you have to reduce the current thru the motor.
- To get back to your question, if the motor doesn't air-cool itself and it can handle 200 mA continuously when running, then it can handle the same current continuously when stalled too.
#2: Post edited
by
Olin Lathrop
·
2021-09-29T14:15:29Z (about 3 years ago)
- That's a marketing blurb. Look at the real datasheet.
- I just checked a polyfuse datasheet, and see that there is usually only about a 2.5 to 3.0 ratio of trip current to hold current. That should be enough to keep the motor from overheating.
- Polyfuses work on heat. When cold, they have low resistance. Over-current heats them up, which makes the resistance go up. It then requires lower current to maintain the temperature that maintains the high resitance.
The main downside of polyfuses is the relatively large series resistance. They may not be appropriate for you motor application for this reason.An electronic fuse, as you seem to have, is a better choice. You can then better control how much current for how long you want to allow. With a properly working electronic fuse, you can use a plain old melting link fuse as a backup, since it should never trip unless there is an outright failure in your electronics somewhere. A stuck motor won't blow the fuse since the electronic system already limits the current and/or shuts down the motor.
- That's a marketing blurb. Look at the real datasheet.
- I just checked a polyfuse datasheet, and see that there is usually only about a 2.5 to 3.0 ratio of trip current to hold current. That should be enough to keep the motor from overheating.
- Polyfuses work on heat. When cold, they have low resistance. Over-current heats them up, which makes the resistance go up. It then requires lower current to maintain the temperature that maintains the high resitance.
- The main downside of polyfuses is the relatively large series resistance. They may not be appropriate for your motor application for this reason.
- An electronic fuse, as you seem to have, is a better choice. You can then control directly how much current for how long you want to allow. With a properly working electronic fuse, you can use a plain old melting link fuse as a backup, since it should never trip unless there is an outright failure in your electronics somewhere. A stuck motor won't blow the fuse since the electronic system already limits the current and/or shuts down the motor.
#1: Initial revision
by
Olin Lathrop
·
2021-09-29T14:14:26Z (about 3 years ago)
That's a marketing blurb. Look at the real datasheet. I just checked a polyfuse datasheet, and see that there is usually only about a 2.5 to 3.0 ratio of trip current to hold current. That should be enough to keep the motor from overheating. Polyfuses work on heat. When cold, they have low resistance. Over-current heats them up, which makes the resistance go up. It then requires lower current to maintain the temperature that maintains the high resitance. The main downside of polyfuses is the relatively large series resistance. They may not be appropriate for you motor application for this reason. An electronic fuse, as you seem to have, is a better choice. You can then better control how much current for how long you want to allow. With a properly working electronic fuse, you can use a plain old melting link fuse as a backup, since it should never trip unless there is an outright failure in your electronics somewhere. A stuck motor won't blow the fuse since the electronic system already limits the current and/or shuts down the motor.