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Discussions Question and Answer Forums Electric Scooter, Bike, and Go Kart Repair Forum

Burned Motor Autopsy

I burned my first motor and I'd like to figure out what went wrong. It was a 36 volt 1000 watt Unite motor MOT-361000B. I had the motor on my all wheel drive electric drift trike with a heavy duty speed controller SPD-241000D and 36 volt lithium battery pack. I was going full throttle for about 5 minutes, traveling over 35MPH on a flat track (lots of fun) but the motor eventually started to smoke. I've had the motor for about one year and was pretty hard on it. I sent the motor up in smoke for this photo below. What do you think happened?


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I'm thinking about replacing it with a Currie motor MOT-SD361000. It looks like the finned aluminum case and neodymium magnets will be better motor for my rugged machines. Will I still be able to use the heavy duty speed controller SPD-241000D with a Currie motor MOT-SD361000? What size fuse or circuit breaker would you recommend?

When a motor smokes like that it is from the insulation on its electromagnetic coils overheating. The coil insulation is made from enamel which is plastic and it will burn if the coil temperature gets too hot. Once the enamel starts to burn off then the copper coil windings inside the motor will begin to short-circuit with each other and cause the coil resistance to decrease which will cause the coils to get hotter and then more insulation will burn off until the motor will no longer work. 


The cause of motor overheating is from the motor being mechanically loaded beyond its self-cooling capacity. To lower the mechanical load on the motor so it will run cooler a lower gear ratio could be installed so the top speed is slower and there is less wind resistance on the vehicle which will equate to less mechanical load on the motor, or a throttle top speed limiter could be installed so motor cannot be driven at full throttle, or the rider could not run the vehicle at full throttle continuously in order to keep the motor temperature down. Another option is to force air through the motor with a fan to help keep the coils from overheating. 

Thanks for diagnosing the problem with my old motor. I made a few upgrades to my all wheel drive electric trike, starting with a new pair of 36 volt 1000 watt Unite motors MOT-361000B from ESP. I attached an air mattress pump with clear tubes to force air through the motors to help keep the coils from overheating, like you suggested.


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I also added some 149 degrees Fahrenheit thermal switches SWT-149DF to each motor using large hose clamps. The wires are connected to the throttle signal for each controller, so if one motor overheats I will still be able to use the other motors to limp back home. 


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Finally I added some 40 Amp circuit breakers CBK-40 in between the battery banks and controllers.


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I also lowered the gear ratio, but only by 15%. Thanks again for the excellent parts and support. I tell everyone that asks, I get all my stuff from "Electric Scooter Parts."

Very impressive. I have never seen an electric motor air cooled with hoses like that - what a great idea. That will provide so much more cooling power than a computer fan strapped onto the back of the motor ever could. I also like the way you used a hose clamp to attach the thermal switch to the motor - another great idea. I have always recommended gluing them on with epoxy but the hose clamp allows the thermal switch to directly touch the motor for better thermal conduction and makes thermal switch replacement super easy. 

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