Melted my 36v motor - any tips on rewinding?

[slippman]

Hi, I run a mid motor kit from gng electric, just the small 36v/250w motor. However, I upgraded to a 48v/500w battery & controller setup... I melted the windings in the motor. When opening the motor you could see that the insulation material between the wire windings and the armature had failed, sending shrapnel into the circulating motor, and destroying the coils that then shorted. So, I was thinking I should try rewinding this motor with higher quality wire & insulators, and also add som alu-fin cooling on the outside and see how it goes. Eventually I might just get a bigger motor, but I'd like to try as I love the stealthyness of this current setup (small motor underneath the BB).

Does anyone know of a good resource on how to size this stuff? I dont know how many windings (maybe I can count the old ones), nor do I know the proper wire gauge going from 36v->48v... any tips? Also, locally (Sweden) I can buy "laquered" or "enamel" winding wire, which has the highest quality and can take more heat?



Thanks! Sebastian

 

[motomech]

Mini-motors are cheap, just get another one.

 

[heathyoung]

Yes, agreed with the above poster BUT - at 48V you have a lot more RPM to gear down, the motor was probably not running in an efficient RPM range so it just cooked itself.

Rethink your gearing - increasing the voltage 25% increased RPM 25% which would have required you to get your gearing up to scratch as well to suit.

That looks like a unite geared motor - From memory its available in two different winds - The 250W gives 320RPM, the 450W gives 550 RPM - both at 24V.

So at 36V chances are they used the low RPM version (I hope) and got 480 RPM@36V, going to 48V would give you 640 RPM (yikes!).

Without the full details of the kit, this is still a WAG (wild ass guess).

If you have your heart set on rewinding the motor, get formers and wire that are rated for a higher temperature, and wind for a lower speed - ie. more turns. There was an old member here (SAFE) who did some work on rewinding these, but don't read any post of his with a graph in it (older ES members will know who and what I am talking about here).

 

[slippman]

Thanks for your input, it is indeed a unite motor. I didn't realize RPM is an issue, I thought current&heat was the main worry... In that case I sould get a new motor, because when running the old one@48v I reached the speed I wanted - about 40kph (25mph)... and it's obviously not econmical to both rewind AND change the internal gearing.
Any ideas on good places to buy unite motors? would like to keep my old brackets and such, and just step up the motor size..

 

[amberwolf]

RPM is an issue *because* of current and heat--if you are still applying full power, and a motor isn't able to quickly get to the higher speeds that a higher voltage allows (forces, actually), then the current flowing thru the motor remains very high for a longer time, causing more heat.

If it can more quickly reach the faster speed, then it's BEMF gets high enough to reduce the current flow, and it doesn't get as hot as fast.