# Better insulation for field coils?



## INCONCEIVABLE (Feb 19, 2008)

Hey all,
I was thinking about wrapping my field coils with a couple layers of fiberglass electrical tape and a couple layers of silicon tape for better electrical insulation. 
I recently upgraded to Enerdel lithium batteries in my Formula EVee. Now the weak link is my 8"ADC motor! 

http://www.diyelectriccar.com/garage/cars/239
http://www.youtube.com/watch?v=g8d2SaHM-MY

I experienced arcing inside the motor case under heavy acceleration, mainly from the back of a brush to the edge of one of the field coils. After disassembly of the motor I also found arcing where one of the copper bolts goes through the case and some small spots from a field coil to the case.
I welded some copper back onto the edge of the damaged field coil and painted many parts with red insulating varnish.
I wrapped this field coil with fiberglass insulating tape but not with the silicon tape yet.

I'm wondering if it might hold too much heat in the coils?

Anybody have any experience with this???

Thanks,
Eric.


----------



## major (Apr 4, 2008)

INCONCEIVABLE said:


> Hey all,
> I was thinking about wrapping my field coils with a couple layers of fiberglass electrical tape and a couple layers of silicon tape for better electrical insulation.
> <snip>
> I experienced arcing inside the motor case under heavy acceleration, mainly from the back of a brush to the edge of one of the field coils. After disassembly of the motor I also found arcing where one of the copper bolts goes through the case and some small spots from a field coil to the case.
> ...


The insulation coating on the magnet wire is very, very good and in most cases needs no additional insulation. Further wrapping insulation over the field coils does inhibit thermal transfer. Adding insulation on top of the wire coating does increase dielectric and wear resistance. This is typically unnecessary. Afterall, you don't have it on the armature.

Back in the day , those field coils were wrapped with half lap layer of glass tape (fabric) and impregnated with polyester resin (used to be varnish). This was eliminated when a method to apply the resin in the frame was developed. Typically Nomex paper is used for barriers where the coils contact the steel parts and the coils themselves only have a few bands of adhesive tap.

Although it probably doesn't matter in well ventilated motors, silicone should be avoided for use in the motor as it can attack commutation. (Note silicone vs silicon)


----------

