Does anyone seal their windings?

[modern_messiah]

Hey all,

Super quick question…Obviously a fair amount of stator rewinding and motor repair goes on around here, so I was wondering if people bother to ‘seal’ their work when done?

I’ve read in a few places (though buggered if I can find them now that I want them!) of people applying varnish to stator coils to provide some scratch resistance.

Is this recommended? I’d assuming by doing this you are reducing your ability to cool the coils – as in the varnish would make it run hotter, which is obviously undesirable. Or do the benefits outweigh the draw backs?

I guess if the motor is sealed up by its housing properly and cared for adequately when apart it’d be a non-issue…

 

[Floont]

The windings are obviously not bare copper, otherwise they would short out.

They are pre-varnished somewhat to keep them insulated from each other for performing the winding process, then more varnish is applied to bind them in place so they do not get pulled out of place by mechanical or magnetic forces.

 

[modern_messiah]

Hi..yeah I was aware that the copper in insulated already, but I meant to protect from larger scratches. I'm just trying to gauge if it's something I should bother doing.

 

[fechter]

I did it on the motors I rewound. It prevents the windings from rubbing against each other and eventually wearing through the insulation. There is a considerable amount of force on the wires, so if they are loose, they will move. With thick heavy wires, it's not as much of a concern.

 

[Floont]

I figured you knew, but it's best to start out with stating the obvious.

In motors and generators it is important that the windings do not move or flex whatsoever. Varnish is an excellent way to accomplish this on the small motors we work with. It is more complex at the MW level.

 

[modern_messiah]

Oh OK then. I think the motor I am considering 'varnishing' may not need it then. The coils are in very tight and certainly won't budge without me tearing the insulation. I might leave it for the time being and if I decide it needs to be done or I get bored then I can give it a go - though that would probably involve me doing a rewind.

Thanks for the info!

 

[Miles]

I’d assuming by doing this you are reducing your ability to cool the coils – as in the varnish would make it run hotter, which is obviously undesirable.

No. Encapsulating should increase the ability to transfer the heat.

 

[Miles]

There is a considerable amount of force on the wires, so if they are loose, they will move. With thick heavy wires, it's not as much of a concern.

As I understand it, there is no force on the wires. All the reaction force is taken by the core (ed. assuming there is an iron core). Isn't this right?

 

[Lebowski]

There is a considerable amount of force on the wires, so if they are loose, they will move. With thick heavy wires, it's not as much of a concern.

As I understand it, there is no force on the wires. All the reaction force is taken by the core. Isn't this right?

No, there can be force on the wires (Lorentz force, see wikipedia).
My motor solely works with Lorentz forces (no metal core), my windings are drenched in epoxy glue...

 

[kannansiyer]

We use thermally conductive but with high electrical insulation resistance with mechanical strength(requires machining to remove) compound. It helps in making the motor water proof also. This is certainly an important part of hub motors.

 

[modern_messiah]

I’d assuming by doing this you are reducing your ability to cool the coils – as in the varnish would make it run hotter, which is obviously undesirable.

No. Encapsulating should increase the ability to transfer the heat.

Not to drag this discussion on longer than need be, but how can this be the case?

 

[amberwolf]

I expect by removing the air gaps within the structure with solid material. Even "insulators" tend to conduct more heat thru them faster than air does.

 

[modern_messiah]

I expect by removing the air gaps within the structure with solid material. Even "insulators" tend to conduct more heat thru them faster than air does.

I guess that makes sense. But this assumes that the sealant is able to get into all the nooks and crannies and does not leave pockets of air everywhere. Meh, I might leave the coating for now becuase I'm not 100% positive that my windings will even remain at the moment. A rewind will be easier if I leave the stock windings as they are...

 

[johnrobholmes]

I encapsulate all the motors I wind, but they are different than the typical motors we find around here. Epic 0140 is a good choice for smaller assemblies, 0131 is a better choice for brushing on as an outrunner or hub motor would need http://www.epicresins.com/electrical_motors.asp

 

[johnrobholmes]

Even better for at home jobs, use a two part epoxy so you don't have to bake the motor. Not as high of resistance to temperature, but great for reducing hot spots and winding vibration


http://www.epicresins.com/electrical_transformers.asp

http://www.aeromarineproducts.com/electronic-potting.htm


Note that most potting epoxies will not be made for thermal conduction. You will pay a high price for the real deal like Epic carries.

 

[modern_messiah]

hmmm...probably a bit hardcore for what I'm trying at the moment. I brought this up because I saw someone using a spray varnich of some sort to do it. I guess that was more of a low grade job - I doubt it would hav eprevented much movement and was more of a scratch resistant system than anything else.

 

[amberwolf]

If the spray varnish is thin enough to run down in between the coils, then sure it'll work; might just take a few coats is all.

 

[fechter]

I just used some old brush-on varnish I had in the garage. It was runny enough to penetrate the windings. Once it dried, it did throw the balance of the rotor off a bit (brushed motor). Not an issue with a brushless motor. It also made a pretty strong smell when it got hot the first few times. I suspect they make a high temperature varnish specifically for motor windings, but the run-of-the-mill wood flavor seemed to work fine for me. You want just enough to stick the windings together. A real heavy coat on the outside will probably interfere with heat dissipation a little.