Should the motor winding be shorted to motor axle?

[danoussh]

Hello people of Endless-Sphere,

I would like to know if it is normal that there is a short/connection between the motor axle/chassis and the phase wires?
Using a digital multi-meter, I'm testing continuity between each of the phase wires and the motor axle/chassis. To be more precise, I cut and removed all phase wires right up to the beginning of the motor winding in order to remove any false positives, therefor my multi-meter probe is measuring at the beginning of a phase winding. The other probe of the multi-meter is touching the axle of the motor. The result after testing each phase winding is a continuity (beeeeep) from the multi-meter.

The original problem, I blew my controller (a few mosfet were cracked open, and three caps exploded and a gate resistor dead.) because of a disc screw that unscrewed it self while I was riding up a hill. The screw cut the protective layer of the three phase wires and I instantly felt the regen come into action upon each revolution of the wheel. So the controller was dead but I luckily managed to replace it. But on my next ride, after about 2km, the bike died on me for no apparent reason except for the excessive heat coming from the motor. At first I though the hall sensors were dead and needed replacement, which I did. But once again I rode about 2km and the regen would turn on for no reason. I let the motor cool down and the regen effect was not there anymore, so I rode again and the regen turn on again only after 100 meters.

I finally got home and started my first troubleshooting steps.

• With everything still connected, no wheel resistance. No regen effect could be felt. Even if I rapidly increased the wheel rotation speed.
• With all phase and hall sensors disconnected, still no regen effect or resistance while turning the wheel.
• This is when I tried to short each of the phase wires to see how they would react, you could definitely feel regen effect for each phase combination.
• When measuring continuity, each phase was shorted to each other and also the axle.
• Tested the same thing but this time with the probe right up to the phase winding.

Any idea?

Specs:
Motor: Magic Pie 3
Controllor: 12 x 4110 MOSFET Extreme Modder Controller LYEN Edition
Bat: 22s8p - Li-ion - Samsung INR18650-25R 2500mAh - 91V full charged - 20Ah
Bike Frame: Rockrider 6.3 2013
Extra: Hall effect thumb throttle, hall effect brake sensors, Cycle Analyst v2.3 (updated to v2.4)

 

[flat tire]

Not good. Your stator wore thru the insulation and is touching the bare wires. Tends to happen with hub motors. In the future you can epoxy the windings. This will help prevent movement that can lead to damage.

 

[billvon]

Any idea?

You have a short between a winding and the stator. It probably doesn't manifest until the wire gets warm and expands a bit.

 

[danoussh]

Thanks for the reply.
So I guess there is nothing else to do than either re-wind the phases or buy a new motor then?

Is it worth re-winding phases?
How can I calculate how much wire I need?

I found this post from @Liveforphysics, what do you think, is it worth trying? Is it that easy to chip enamel?
If I understarnd correctly, must not chip the enamel either against the stator nor against a previous turn of winding. So by following Flat Tire's advice, I can at least epoxy the whole stator.

It's so difficult to wind, don't bother if you are not expert and dedicated. I personally gave up after failure to get a single tooth without chipped enamel.

Edit: Just found this post, i'm reading through it hoping to find some answers.
https://endless-sphere.com/forums/viewtopic.php?t=34750

Edit2: I don't think I'm ready for winding my own motor. Maybe I'll give it a try some day, but at the moment I need a bike as it's my only daily driver.

 

[flat tire]

Rewinding tends to be difficult and extremely labor intensive, especially if you have no experience. I don't recommend it. Get another motor, look into impregnating the windings with high temperature epoxy to guard against this issue in the future. If you do want to rewind the motor, you can try using paper between the stator and windings as additional protection.

 

[neptronix]

I wouldn't bother rewinding it because new magic pies have 0.35mm laminations and the performance and efficiency will be significantly better.

A 30mm wide DD ( MXUS, 9C, leafmotor, etc ) would actually have as much continuous power as your magic pie did ( because thin lams ), so you can either gain more power by going with the same size motor, or keep roughly the same power and lose weight with a new motor :thumb:

 

[Volt_Ampere]

If you don't know exactly what you are doing, rewinding will not go well. Buy a new motor.