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Test load for motor controller

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tobi:
Hello,

I have motor controller design. I have to write software and during this time I don't want to have a real motor standing next to me (36V/40A/2mH). So my idea is to use a passive RL load.

My question:
- What kind of inductor do I have to use (air coil, ferrit)?
- Do I have to be careful with something like staturation, L over I characterisics?
- Where can I get an inductor like this?

Thanks.

MagicSmoker:

--- Quote from: tobi on July 09, 2019, 01:53:14 pm ---I have motor controller design. I have to write software and during this time I don't want to have a real motor standing next to me (36V/40A/2mH). So my idea is to use a passive RL load.

My question:
- What kind of inductor do I have to use (air coil, ferrit)?
- Do I have to be careful with something like staturation, L over I characterisics?
- Where can I get an inductor like this?

--- End quote ---

Real motors experience saturation to some extent during normal operation so a gapped core inductor would be best in that regard, not to mention you would need several hundred turns to get to 2mH with an air-core solenoid (even more for an air-core toroid). However, it's going to require a really large core to handle 1.6J of energy storage... Also, an RL load basically simulates a motor when it is not spinning - no back EMF, of course - which means your motor controller is going to be operating over a very limited duty cycle range.

You will almost certainly have to wind this yourself, because a 2mH/40A inductor is not an off-the-shelf item.

As for making it an air-core, that's going to take a few hundred turns... like 400+. Yikes.

EDIT - finished sentence that I left dangling earlier.

capt bullshot:

--- Quote from: MagicSmoker on July 09, 2019, 02:18:04 pm ---You will almost certainly have to wind this yourself, because a 2mH/40A inductor is not an off-the-shelf item.

--- End quote ---

Not a big deal, (at work) we use such stuff on a regular basis, and one can buy them from transformer manufacturers (the typical three-leg inductor / transformer for three-phase current).
Normally these things are used as an additional feeding reactor to somewhat larger VFDs, but they also nicely double as dummy loads for the VFD. One can push the nominal output current into these without burning all the real power into resistors, usually this is sufficient for load testing / thermal cycle testing of the VFDs, but not for testing the control algorithm. You want a real motor here (for SW development purposes).

MagicSmoker:

--- Quote from: capt bullshot on July 09, 2019, 02:30:23 pm ---
--- Quote from: MagicSmoker on July 09, 2019, 02:18:04 pm ---You will almost certainly have to wind this yourself, because a 2mH/40A inductor is not an off-the-shelf item.

--- End quote ---

Not a big deal, (at work) we use such stuff on a regular basis, and one can buy them from transformer manufacturers (the typical three-leg inductor / transformer for three-phase current).

--- End quote ---

Yes, good point - there just might be a line/load reactor available off-the-shelf that meets the OP's requirements. Not the usual 3%/5% impedance types, though, as they are only available in discrete amounts of inductance inversely proportional to current rating.

patrick1:
with respect, - go too the local scrap metal guys,  and stick a motor between your legs.   hold on tight @@

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