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DC motor core insulation from windings? Answered

I have recently attempted to rewind an old 240V AC drill motor to a low voltage DC one. After winding the 12 coils I found that all of the windings were shorted to each other, I'm assuming this is due to the thin enamel coat on my wire breaking against the edges of the steel core.
As a result I need to rewind it, but I am unsure what kind of insulation to use, tape, some kind of glue or sealant, varnish, I was thinking a hardware store type product nothing online or that costs a lot. 



Best Answer 6 years ago

Winders use a pre made slot liner using fish-paper and when the coils
are all inserted a top stick of fiberglass folds the coil in place.

The next step is to heat the frame and windings to be drip coated with
epoxy to harden the slot wires.  This prevents vibratory rubbing of wires
leading up to a short.


slot liners.jpgSlot-liner-paper.jpgcoilset.jpg

I thought of doing something like that but I am somewhat limited with winding space and this method might not leave me enough space even after reducing the number of turns from 20 to 15.

Here are some pics of the failed windings, 0.54mm wire.


Nice job winding try end piece insulators to save the winding edge.

And you can powder coat insulate the slots of the armature before
winding then press the commutator on after winding and then varnish.



Don't forget top sticks to keep the wires inside during rotation forces.

Where can I get material for end piece insulators and where can I get powder coat insulation from? Might motor rewind stores have this that they will sell me?

What are top sticks?

Small motor manufacturers for the end pieces and rewind shops or metal
fabricators for powder coating.  And there are rugged grades of enamel 
insulation for magnet wire ( a name I recall ==>  poly materialize ).

The old wire gauge was very thin....yes ?  and the commutator had many
copper bars. 
You know that a 12Volt armature does not need as many copper bars but can still use the high volt commutator if you have only that.


The old gauge was 0.28mm wire. Pics of the commutator are below (24 bars).

And what do you mean by 12V armatures do not need as many bars?


Bar to bar voltage for 240 worst case is :
2 bars shorted under each brush leaves 20 bars each side 240v/10 bars
remains 24volts ( for arcing ) bar to bar.

Same condition 12v/10 bars is a measly easy 1.2volts bar to bar.
You could use a low cost ( cheep ) 12 bar commutator.
That would give you 12v/ 6 bars a mere 2volts bar to bar :-)

Also put a shrink tube ( insulate ) on the armature shaft where
the coils cross over.

After every thing is done & armature is ready for motor, do one more operation.
put armature in a lathe and shave a mm from the commutator for a true
round ride for the brushes. Make sure no Cu smears and has a bar bar short.

A wise man giving advice when asked, can a man carry a cat home by holding it by the tail replied "let him, because he is getting 60 to 70 times the experience of a man who does not !! "


Well I'm thinking that this will be a prototype for a larger circular saw or vacuum cleaner motor that I will modify (hope to compare with a regular 12-24V electric scooter motor).

With the commutator bars are you suggesting that considering that the coils are in series there will be an undesirably low voltage across each one? (If so I am sure I can run it off 24V).

Also If I were to use a different commutator I don't think it would work out due because that would mean that I would need to have the coils in parallel and series.

Not at all......
A 240v commutator is the harshest application for a fractional horse power
dc armature.  I was demonstrating how safe your 12V application is and
giving you engineering acumen not available in other text..

Manufacturers pay 3X for a 24 bar commutator over a 12 bar.

The only benefit to your situation, if you had a new 12 bar commutator, is
the fact you would only have to wind 12 coils.



Ah. So 24 bar commutator = good, I should have read more carefully.

Also I got some insulation paper today and it turns out to be much thinner than I thought It would have been so I'll give it a try.

Thanks for the help!

Also I called up a local motor rewind shop and they are willing to give me insulation paper, I would prefer the powder coat insulation but I may as well give the paper a shot since I have a chance.

Winding shops are a dirty job, bring them a 6 pack of local beer.

usually its a piece of thin card or paper stuck over the metal just to prevent its edges gouging the copper enamel. Often the coils are sealed in varnish after they're wrapped to give them extra protection/physical strength from the large forces when the motor is operating.

I thought of doing something like that but I am somewhat limited with winding space and this method might not leave me enough space even after reducing the number of turns from 20 to 15.

Here are some pics of the failed windings, 0.54mm wire.

+2, one to A and one to F......

+1 to MadScientist for attempting to rewind a motor ! Brave man !