My Motor Died

[4Springs]

I had to call the RACT today and be towed home!
I heard a noise, then the light came on on the dash that indicates the thermal switch on the motor has closed. This is a switch in the motor somewhere that I connected to a likely-looking disused dash light.
I coasted to a stop and opened the bonnet. Could smell a burning smell. Tried to run the motor in neutral but it did not turn at all.

Once I was home I took off some covers and had a look. Found that one of the four sets of brushes was lop-sided, and one of the brushes was disconnected.
The motor is a Kostov.

1st photo is of the two brushes I took out (they sit next to each other). The longer one is more or less how it should be, but the other one has been warn right down. It was jammed in its cradle on an angle. You can't see it from the photo, but the lug on the wires on that one is quite bent as if it had been hit, or probably pulled by the brush.



Next photo shows the thing the brushes sit on, as well as the bracket for the brushes I removed. I don't think there is any damage here. I felt for score marks with my finger and didn't feel anything.



The next photo shows one of the other three sets of brushes. They all look undamaged as far as I can see.


The last photo is of the bracket again. It looks a bit lopsided, but so do the others.


I've taken the brushes out to see if my local motor re-winds workshop can supply replacements.
Any advice is welcomed.
What could cause this?
Do I need to replace all the brushes at once?
Am I likely to get replacements locally, if not where would I go?
What do I need to know about installing new brushes?
Is there any other damage I should be looking for while I'm in here?

[evric]

I had a problem the the top set of brushes in my ADC X91-4001 motor and had replacements made by cortela.com.au Ron Rigg (0432762530) is my contact.
I replaced all the brushes at once, but then bedded them in for about 20 days continuous running on a 12V power supply (about 40Amps)
See YouTube video Barina EV.
The spring tension needs to checked so that it is the same on all.
The problem may have come about from the brushes not being bedded in in the factory. I reckon that was my problem.

[nuggetgalore]

I had to call the RACT today and be towed home!
I heard a noise,
Do I need to replace all the brushes at once?
Am I likely to get replacements locally, if not where would I go?
What do I need to know about installing new brushes?
Is there any other damage I should be looking for while I'm in here?

I would not spend time and effort in replacing the brushes without making sure there is no damage to the commutator. If only one segment is dodgy,it will burn out completely or rip it and its neighbors out. The commutator probably needs to be machined, looks rather shocking.

[Johny]

I agree with Andreas. That commutator looks pretty burnt.
My GUESS is that the brush stuck in the brush holder, overheated, burnt the comm, and finally fractured from the heat. Just a guess though.

A good motor shop will test the commutator and, if good, machine it slightly to clean it up. My guess (again) is that the comm is still good provided the segment insulation is still OK - not too burnt.

Again, the motor shop should be able to get replacement brushes that can be ground to size.

[Richo]

I'd probably take a look at the spring assembly.
If one side is pushing much harder then it will wear out quicker.
Then the brush went past it's wear limit and rattled around until it jammed up on the commutator.

The bracket the brush sits in one side of the top is shiny like the spring had been resting/bouncing on it as the brush had worn down too far.

Just as a side thought there are 4 sets of brushes.
Shouldn't it still run, with reduced power, with 2 sets removed?

There's probably an excess of carbon buildup on the commutator.
Wiping it of with IPA or blowing out with on air gun may help.

[Richo]

Also any ideas how may km you racked up before it blew?

[4Springs]

I'd probably take a look at the spring assembly.
If one side is pushing much harder then it will wear out quicker.
Then the brush went past it's wear limit and rattled around until it jammed up on the commutator.

The bracket the brush sits in one side of the top is shiny like the spring had been resting/bouncing on it as the brush had worn down too far.

I like this theory, the motor rewinds guy did too. You can see that one of the springs is sitting at a different angle than the other one. The end of one of the springs was also burnt off by arcing.

I took the brushes and springs to a local motor place, along with the above photos. For some reason I had deleted the photos from my phone, so I had to bring up this forum to show him the pics!
He said that yes, he'll be able to get some brushes made if I can get him all the specs on the motor. He said that from the photos the commutator will need to be machined, and that if I get it turning (i.e. with the new brushes) he can give me a thing to do that with (sounded like a sharpening stone).
He looked at the picture of the un-damaged brush and said that it would be best if I replace all of them.

With regard to Eric's comment on the bedding in brushes, I watched his video when I bought this motor. I went and watched the motor in the dark and could see no sign of any sparks. So I decided that the brushes were bedded in ok.

I've also called Tim at EV Works to see if he has brushes. He hasn't called me back, so I guess he doesn't have any in stock. He did say that he had a local company that could make them.

This motor is only new, it's done 22,000 km.

[evric]

Hi Christopher,
In my video the sparking stopped at 21 hours of "bedding in" and then the brushes required another 249 hours of "bedding in" until they matched the commutator.
My motor had done less than 20,000km before the brushes were distroyed.
Eric

[Johny]

A lifetime ago I user to do field service on 150HP DC Motors - in extruders and suchlike.

When we changed brushed we had a bedding stone that we simply held on the comm (with the motor running slowly ~= 500RPM) for 30 - 60 minutes until the brushes took on the shape of the comm. (We stopped motor every few minutes and had a break while the brushes were partially extracted and checked.)

I guess these motors were never exposed to the large overloads that EVs subject them to, but we never had a failure after brush replacement.

Bad brush fitting (by factory sparkies), sticky brush holders and detensioned brush springs (due to taking partial motor current) were the major problems.

Even if someone expert replaces the brushes, check them yourself for correct fit and sticking (lift slightly by pulling on brush wires).

I guess that's why I went AC

[Richo]

20,000km is a rough yearly travel for an average commuter.
What is yearly servicing like on an ICE? $200-400/yr
So I guess if the brush set was less than this then your still in front from a maintenance point of view.

I guess it's just the inconvenience due to usual repair work required.
You could always buy another set once the first set is up and working.
That way if it happens again you could be up and running in no time.

[Johny]

The brushes aren't worn down though. This was a failure.

[4Springs]

I just remembered - I have a set of brushes in the shed!
This is because I have a burnt out Kostov K9 motor. I replaced the K9 with a K10 so that I wouldn't burn it out. Same manufacturer, would they just use the same brushes in all their motors?
So I went and had a look, pulled out a brush and took it to the K10. The K9 brushes are similar in all dimensions except for width. The K10 brushes are significantly wider, with much thicker wires on them. The K9 brushes would rattle around in that cradle.

The bedding stone that Johny mentioned sounds like what the motor rewinds guy was talking about. How do you hold it on there without getting yourself electrocuted?

[Johny]

I have a vague memory of strapping it to a piece of wood.

I also have a clear memory of blowing the s%&t out of an SCR controller when it slipped and somehow lifted a brush momentarily (or something - can't remember why). It wasn't me holding the bedding stone...

[4Springs]

Ok, still waiting for anyone to return my calls on getting brushes.
In the meantime, and as suggested, I cleaned out the commutator using compressed air and then isopropyl alcohol. Then I inspected it carefully and took some photos:







There was a lot of dust. I suppose you get that when you have worn one brush down by about 2/3. Now that I've done this I realise that this is something I should have been doing periodically (blowing it out with compressed air). If I had done so I might have noticed something funny about the dodgy brush.

In that third photo you might be able to see a line along the middle. I assume this line is from between the brushes. I assume that eventually, after many years work this line would become pronounced. At the moment it is just a line.
The commutator looks intact and feels very smooth. There are some notches though, that can be seen on the third photo in particular. I can feel these with a fingernail in the groove, but can't feel them with the balls of my fingers over the surface. They are not just slivers, they don't come off with my pick tool. They mean that the sections are closer together than they should be - is this something that should be fixed?

Then there are these bits:





Having never inspected this bit before, I'm not sure if this is how it always looks. Parts look as if they have had their lacquer knocked off but I don't think there is any underlying damage there.

[Johny]

You haven't mentioned any discolouration of the windings so I'm assuming that the copper wire generally looks OK. That commutator looks like it needs a light skim to be. It looks a bit beyond normal "hard use" (see pic following for guide) but my experience is with motors that operate within their ratings and EVs definitely don't.

You mentioned that you have contacted a motor repairer so I'd show them your pictures as the pics show a good amount of detail.

[4Springs]

Ok, so this is taking ages to get brushes made.
The local motor repair place has advised that their supplier has advised that their (overseas) supplier has advised that the brushes will not be delivered until the end of this month, or possibly the start of April.

I have car shows to attend!
One last week, one this week, one next week and one the week after.

The one this weekend is the biggest one and I've decided to trailer the car there.
Richo said above that the motor should work after a fashion with two sets of brushes. Is this correct? (he seemed a bit uncertain, and I'd like a bit more confidence in advice before I try anything!) If I could get it to move under its own power it would make it much easier to get on and off the trailer, then into position at the car show.
If so, which of the remaining three brushes do I remove?
How much power would I have - half?

[whimpurinter]

I wouldn't buy a brushed motor.
I remember the generators on the cars of the 60's.
I remember a vw with worn brushes and an eccentric commutator.
Never mind having to replace the brushes.
The idea of sparks flying is irksome.
Don't like 'em.
Imiev, Vectrix, leaf blower, whipper snipper, drills. All the others got the brush (sorry).

[jonescg]

You should be able to drive slowly on two brushes. But what a pest! I'm surprised nobody in the Associatuon can help you. I reckon there would be more than a few DC vehicles sitting idle year round which could lend you a set of brushes?

[Richo]

Half the brushes half the power.

I would think that the set on the opposite side (180 degrees) to balance.
Hard to know without looking at the commutator config.

Hang-on just taking a call to disarm a bomb over the phone...

[Richo]

Sample photo taken from here:
http://www.diyelectriccar.com/forums/sh ... 88672.html

[Richo]

ha ha I see you have already got a photo...

viewtopic.php?title=kostov-kelly-postmo ... 333#p53693

[4Springs]

Ok, I chickened out of trying two brushes. My local motor guy didn't like the idea and I didn't have a lot of time. So I managed to trailer it to the car show without it going.

But now the brushes have arrived. Two months after I ordered them!


Notice the ridges on the face of the brushes. Designed to wear in quickly.
Because they were taking so long I ordered a spare set. So 16 brushes and springs cost $720. This is a significant percentage of the price of the motor (about $2000 from memory). If anyone is reading this in the future and needs a set of brushes hit me up!

Removing the other brushes I found another one had burnt through the wire. This was the one with the over temperature switch on it. The opposite of the other burnt one.
Several of the brushes were misshapen and did not come out of their brackets cleanly. Then those brackets needed to be bent a little to make room for the new ones. The brackets are very soft (brass?).

The motor guy gave me a piece of commstone to clean up the commutator. It wasn't very long, and he said it can get a bit hairy trying to use it amongst the voltages, so he recommended attaching it to a piece of wood with tape. I was a bit dubious but had a go.




Then I had to make the motor turn. Evric said he used a 12V power supply I think. I don't have anything that beefy. The motor guy said to run it flat out to use the stone. So I just used the throttle. Very technical.

I had bought an optical tacho from ebay for this, so I was able to wedge the throttle open at an angle that gave me about 3000 rpm. That was fast enough for me.
No sparks, not noisy at all like in Evric's video.
I was able to use the commstone. I was expecting it to be hard, but it wore away very quickly. Cleaned things up nicely.



The stick worked perfectly. I was able to move it around to clean up any section I liked.
I'm now sitting in the garage with the laptop, keeping an eye on the car as it sits there at 3000 RPM. Is using less current than my ammeter can read. My ammeter can read the current when charging, so it is not using much. Looks like it would easily run all night on the battery but I'm not game to leave it. Don't know how long I should run it for. I'm not about to take out a brush to inspect it - they are really hard to get in!

[evric]

Hi Christopher,
The only way to tell is to take a brush out and inspect it.
My brushes came with curved faces close to the finished requirement and still took 270 hours of constant running to match the commutator.
Your commutator came up nice.
Eric

[4Springs]

The only way to tell is to take a brush out and inspect it.
My brushes came with curved faces close to the finished requirement and still took 270 hours of constant running to match the commutator.

Hmm, yes, but how bad is it if they don't exactly match?
After 5 hours there are no ridges on the leading edge, so it has worn down that far. There are still ridges on the trailing edge. My guess is that once I can't see ridges any more they'll be pretty close to perfect. That will presumably take a while now, since it has started wearing down the main part of the brush, not just those ridges.
But what is the risk if I drive the car before the brushes are completely bedded in? I imagine that the surface would look flat on the leading edge, with the rest of the brush touching the commutator but with the remains of those ridges getting deeper as it goes toward the trailing edge. So I reckon it would be pretty good now, but will get better as I run the motor. Driving the car is still running the motor, but with more current and with a constantly changing motor speed.

[4Springs]

Here is a photo of the commutator after about 5 hours running in. What else am I going to do while I'm out here in the shed keeping an eye on it?



On Johny's chart this looks like "underloaded operation". Well I'd agree with that, it is just spinning. Like he said though, that chart is for motors that run within their specifications. If I drive the car then I'll be drawing more than the rated current...