How do you varnish motor windings?

[nasukaren]

So I bought the HXT outrunner motor that Scott's been talking about..... it arrived in stellar time, now I'm just waiting for the ESC and servo tester.

I noticed the windings weren't varnished.... they look like bare copper. Should I varnish them? If so, with what? Just old varnish that I get at the hardware store? Should I just paint it on with a brush?

Thanks in advance!

 

[rkosiorek]

shellac is what is used for the insulation. there are special varieties that can survive high temperatures. the electronics industry uses specially formulated shellac that has good insulating properties as well as with resistance to heat. it is available in many colors, blue, green, red and yellow that are plainly visible. they also make one in a color called "water clear". guess what, you can't see it. but it is there.

the windings do have insullation, probably clear, otherwise it would not be a winding but a dead short.

rick

 

[fechter]

So I bought the HXT outrunner motor that Scott's been talking about..... it arrived in stellar time, now I'm just waiting for the ESC and servo tester.

I noticed the windings weren't varnished.... they look like bare copper. Should I varnish them? If so, with what? Just old varnish that I get at the hardware store? Should I just paint it on with a brush?

Thanks in advance!

My guess is they don't need varnish or they would already have it. As long as the windings are tight and can't vibrate or rub against each other, it won't be a problem.

If you can wiggle the windings, then it probably needs varnish.

I have varnished the windings on motors that I rewound. They acutally make a special motor varnish that withstands high temperatures. For extreme applications you want the "class H" stuff.
Regular varnish is OK as long as the thing does not get too hot. High temperature, runny epoxy is good too.

edit: OK, shellac, but for some reason everybody calls it varnish.

 

[MidniteTweeker]

Something people tend to overlook about a winding is that when it's in operation, the electric current in the winding produces a strong magnetic field which interacts with the field produced by the permanent magnets. This is what makes a motor work, after all. Each individual turn of wire contributes its own fraction of the total force. The amount of force exerted on (or by) a single turn can be surprising. And if a turn is loose it can incrementally flex, rub, and eventually break as magnetic force repeatedly stresses it.

Some wire is coated with a material that can be heated and reflowed by passing current thru the wire. Supposedly this melts and adheres all the individual turns together in a solid mass when it cools. This takes the place of varnish. I've seen it used on lighter gauge (~22 ga) wire and the entire reflow process for an individual coil only took a few seconds. It was rated to 155C. Not sure if it's used on the heavier stuff. Your local motor rewinding shop probably knows more about it.

If I was rewinding a motor I would absolutely varnish the windings. Once I'd invested all the time & effort to reach this point adding varnish would be a no-brainer. If I had Hall sensors I wouldn't limit it to only the windings, either. A little extra moisture proofing wouldn't hurt a thing.

MT