Motor Brushes?

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Motor Brushes?

Postby Scooterman » 27 Apr 2019, 10:05

Hi, I'm refurbing my little scooter at the moment.

The motor brushes don't look too good, although they're not that old. I wonder if the uneven wear is caused by overspeed going down steep hill?

When brushes are new I think regen braking can hold scooter at 4mph down steep hill, but as they wear overspeed creeps up, which causes more wear, which causes more overspeed, etc, etc, until I crash and killed hanged

So questions are...

As there looks to a lot of meat left on brushes can I square the end off on a bench grinder?

Two, if I buy replacement brushes why are mine a golden colour? I thought brushes were all graphite grey. In fact I've seen some similar power tool brushes in grey which are cheaper than my gold colour brushes. But I'm wondering if mob brushes have to be more robust?

When/if i fit new brushes I plan to go slower downhill so overspeed and excessive brush wear doesn't happen. It only occurs if I barrel down on full throttle.

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Re: Motor Brushes?

Postby Burgerman » 27 Apr 2019, 10:15

Those brushes look knackered. Also they are short. And chipped... Caused by heat damade due to inadequate pressure or short length. Or chattering. That short length reduces spring pressure, and they no longer sit square enough in the holder either. And you cant square the ends as they need a large curved contact area on the commutator. Which should be copper/light brown coloured and not raged, burned etc. Throw them away.

They should look like this: -- view images... Yours are the overheated ones. https://www.nithsdale-wheelchairs.com/p ... units.html



A commutator that doesent run true, due to wear or worn bearings, can 'shake' the brushes off the surface and result in the runaway you describe. Since the battery is 24V and an overspeeding motor generates more than 24V a runaway cant really happen otherwise. Overspeed does not damage your brushes. It happens BECAUSE theres a problem with brushes or motor already.

So the solution is replace motor if theres bad commutator or bearings that stop it running totally true or if burned or damaged. And new brushes used carefully for a week until they bed in and contact the commutator properly if the rest of the motor is good. What causes brush damage is usually current. As in steep hills or heavy acceleration. And the heat burnes them... Then they can get short fast. So at very least replace and run at low load (avoid hard acceleration or hill climbing/ramps etc) for a bit. I actually lift the wheels of the deck, and run at low or zero load and max speed for a few hours when I swap brushes.

They are SUPPOSED to look like this, where the curve fits the commutator. Be sure your commutator is not damaged. I would expect it is. Use a torch/flashlight to examine as you turn the motor.
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Re: Motor Brushes?

Postby woodygb » 27 Apr 2019, 10:35

Motor brushes come in many different materials.

http://www.morganelectricalmaterials.co ... roof_0.pdf
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Re: Motor Brushes?

Postby Scooterman » 27 Apr 2019, 11:23

Thank you for your reply BM, I appreciate it :thumbup:

I just had a look through one of the brush holes, the commutator is very dirty. Also I held a wooden chopstick in my teeth, put it through the brush hole, and spun both wheels. I had to do it that way cos when I spun just one wheel the motor didn't turn, I assume something to do with the diff?

I could feel it notching on the segments, but difficult to tell how rough it is?

Removing the motor looks easy, but I don't know how easy it will be to remove the commutator end cap? Might there be circlips, and bearings that need pulling off the shaft?

Thank you for the pdf link Woody, I shall have a read :thumbup:
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Re: Motor Brushes?

Postby Scooterman » 27 Apr 2019, 11:32

This is the motor. Removing the end cap looks a bit more complicated than I thought :problem:

Still, i might have a go.

Image

This is as far as they go stripping down in the service manual.
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Re: Motor Brushes?

Postby Burgerman » 27 Apr 2019, 12:47

Its a toy. Its not adequate. Best bet get a replacement. Long bolts hold it together.
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Re: Motor Brushes?

Postby martin007 » 27 Apr 2019, 21:05

Those brushes look really bad.
You have to buy new ones.
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Re: Motor Brushes?

Postby Burgerman » 27 Apr 2019, 21:22

If the brushes are as overheated and damaged as they are, theres a really good chance that the part that they run on is also burned or blackened or eroded and damaged. So first we need to check it. It may just need some treatment with abrasive paper. Or it may need replacement... As in new motor. The motor isnt adequate by design to take the Amps that it has been asked of it. Hence brushes. Its why we use 4 pole motors on heavy duty chairs. Each brush then takes half as much power individually.

Bad and OK.
Extreme difference here to demonstrate. The one on the left? Burned and worn. Either problem, throw it away. Check for missing or damaged bars too!
The one on the right, can be cleaned up with fine abrasive paper with care, ready for new brushes. Easier to do in a drill or a lathe with a strip of abrasive paper. If it looks like new, just light brown where the brushes run, thats normal, you can just fit a new set.
http://www.golfcarcatalog.com/golf-cart ... bels-2.jpg
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Re: Motor Brushes?

Postby Andrey » 28 Apr 2019, 11:51

I replaced brushes recently and new brushes has much thinner copper wire inside the spring. Does it matter?
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Re: Motor Brushes?

Postby Burgerman » 28 Apr 2019, 11:54

Yes. All the current your motors draw when stalled or climbing a ramp, up to 100 Amps or more, goes through that wire... Take a look how thick the motor wires are and realise that those get hot and smell under load Most of these amps should go through the thin wire. If it doesent then the spring takes some. And the brass housing transfers some to the sides of the carbon brush and all this causes heat. And the spring loses its temper. And or melts and it all goes bad eventually if unlucky.
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Re: Motor Brushes?

Postby Andrey » 28 Apr 2019, 12:01

Burgerman wrote:Yes. All the current your motors draw, up to 100 Amps goes through that wire... Or most of it should. If it doesent then the spring takes some. And loses its temper. And or melts and it all goes bad eventually.


This is old (replaced) and new. I think both looks pretty bad. Old one is very worn-out, and new one seems too weak :(
Do you recommend to find something more appropriate?
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Re: Motor Brushes?

Postby Burgerman » 28 Apr 2019, 12:03

If you can find better fit. If not, no choice.

Those are cheap chinese made copies. Although if you look carefully at the new one it does say 100A on it... Although the chinese seem a little 'optimistic' with all ratings, capacities, etc. It doesent look as heavy as the original. So who knows! Use for a month and take a look at how they are doing.
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Re: Motor Brushes?

Postby Andrey » 28 Apr 2019, 12:15

Burgerman wrote:If you can find better fit. If not, no choice.

Those are cheap chinese made copies. Although if you look carefully at the new one it does say 100A on it... Although the chinese seem a little 'optimistic' with all ratings, capacities, etc. It doesent look as heavy as the original. So who knows! Use for a month and take a look at how they are doing.


Yea, I don't believe in 100A either. Thank you, I'll try to find something better.
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Re: Motor Brushes?

Postby woodygb » 28 Apr 2019, 12:44

Those brushes are rubbish ... get the correct ones.
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