Are stepper motors repairable?

I ordered 4 used Nema 23s for another project (see new version here: ). I could not turn the shaft on two by hand. I even clamped some locking pliers to the shafts and held the motor such that the pliers were perpendicular to the direction of gravity and the shafts wouldn't turn! This was with the motors unconnected. I connected each motor to a DRV8825 that I had (underpowered it with about 2 amps of a 2.8 amp max). The two motors that i suspected were bad just hummed but didn't move. The other two spun fine.

I took one of the bad ones apart and it seems like the stator poles are maybe putting too much tension on the rotor. I can't be certain that this is the problem, though. I pulled the rotor entirely out of the case and the bearings are fine.

I have the expected resistance accross the coils of the good and bad motors.

The seller was nice enough the refund the cost of those DOA motors, but I would like to get them to be more than a paperweight. Any ideas?

Edited 1 time(s). Last edit at 06/12/2015 12:32AM by DRobs86.

2 out of 4 motors are unusable? The supplier obviously has zero quality control. I'd say you'd better find a better motor supplier (which shouldn't be too hard considering how awful the one you bought from is).

If the shafts won't turn it seems most likely it's because the bearings and rotor axes are not lined up. Make sure the bearings are pressed all the way into their fittings, and of course, check each bearing to make sure it spins freely.

Thanks for the reply.

I want to be fair to the manufacturer by pointing out a revision I made to my original post. I bought these motors used on ebay from a reseller who claimed to have pulled them off industrial equipment. He's the one with no QC. (Seriously, if you are going to sell used steppers at least spin the shaft before you claim they work!).

I'll check alignment. It seemed like everything was lined up but I know it takes more than just an eyeball check. Bearings are spinning just fine. Is it possible that heat warped the stator poles causing them to press upon the rotor? Should the stator poles and rotor make slight contact or no contact at all?

One failure mode of steppers is overheating, melting the internal plastic bobbins the windings are on, deformation and lockup . . . . which sounds exactly like what you may be looking at. If they show no signs of deformation/heat damage, the coil resistances are OK, and you can get one aligned, you might be able to run it, but most steppers are not made for adjustable alignment.

And no, there should be *zero* internal contact between parts . . .

- Tim

... stepper will block, when iron or other magnetic chips finds their way in the slit between stator and rotor-magnets ...

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Viktor
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Quote
DRobs86
Is it possible that heat warped the stator poles causing them to press upon the rotor? Should the stator poles and rotor make slight contact or no contact at all?

Yes, possible, and no, they definitely should not touch.

Kudos for sourcing scrapped industrial parts! My machine wouldn't exist without them, many sourced via ebay.

It is unclear to me if you know for sure that the parts were touching? How did it go with taking the motor apart? Did it go smooth? Have you tried to reassemble it after taking it apart and testing again? As VDX says it might just have been some foreign particle and now it could even be fine.

Can you post photos of the stator and rotor?