OT commutator wear

hi, just got a Redi-Line inverter from eBay ("DA12L-1600-A-1")

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i started removing the brush covers to do an initial inspection. when i took out one pair of carbon brushes i could see one was missing and the other was damaged. also noticed the commutator (or whatever it's called) is (badly?) worn and gouged. the one brush that was missing the steel spring was protruding from the brush holder and jammed in such a way that it touched and wore against the copper commutator. you can see the part of the other brush holder (white) behind the copper commutator, there are two brushes in each holder on both sides of the commutator. what i'm wondering and would like to ask here is do you think the wear (in the photo) would necessitate complete disassembly of the unit and take the armature into a electric motor shop to have the commutator turned/repaired/smoothed? is there a simple way to smooth it out while it's still in place that i can do at home without having to disassemble the unit and take it to a electric motor repairman? (i'd imagine it's knackered and being that rough will eat up any replacement brushes i'd ever put back in it.) (i assume it's probably impossible to tell from a photo how badly the commutator is damaged, i was hoping maybe there'd be like a "black and white" situation here, either "it's ok" or "you HAVE to get it smoothed out")

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thanks.

b.w.

(i guess my second question would be how in the heck did the brush get out of it's holder in the first place!? the only thing i could think of is someone opened it up and didn't put it back together correctly, left the brush dangling out of it's holder when they reinserted the brush holder and it got whacked off and as it went flying off it hit the other brush too and damaged it.)

Reply to
William Wixon
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First of all, that's not the commutator that's scored, it's the slip ring. Second. you SHOULD be able to smooth it out with crocus cloth (or possibly aluminum oxide first). Do NOT use emery in a motor , generator, or alternator.

Reply to
clare at snyder.on.ca

According to William Wixon :

It is called a "slip ring". A commutator has many segments and switches which winding is being powered as the motor rotates. Slip rings maintain connection to the same winding throughout the rotation of the motor.

How big is this thing? If small enough, you could mount the rotor on your lathe and skim the slip rings with a very sharp and rounded edge HSS tool. If you don't have a lathe, or if it is too big, I would suggest taking it intact to a motor repair facility, as they may also be able to replace the (probably) damaged brush holders.

The only things which I can think of would leave abrasive grit in the motor, leading to its early demise.

It looks bad to me. I would not attempt to run it with new brushes without re-surfacing the slip rings. And I'll bet that it would look a lot worse with skimming lighting instead of the straight down the bore lighting which you got from the camera's built-in flash. :-(

[ ... ]

My guess is that it was allowed to run past a safe level of wear on the brushes, and the one brush started to tilt in the holder, digging in with the leading edge, and perhaps augmented by an excessive current through the brushes. Eventually, it got so short that it tilted enough to get broken off, thus carrying parts to damage the other brush or brushes.

It could just as easily have resulted from the brushes wearing too short.

Did you download the service manual? Go to page 24, and you will find this paragraph:

====================================================================== Damage to the commutators may occur if the brushes are allowed to wear down below 0.56-inch minimum length. This minimum length applies to both AC and DC brushes. ======================================================================

which sounds to me like what has happened. Measure the length of any intact brushes present.

Note that for a worn commutator, it recommends "turning and undercutting". The undercutting only applies to true commutators, not slip rings such as you have shown here. (But I'll bet that there is a real commutator in the other end of the device.) They seem to use the term "commuator" for both ends. Well -- it is their product. :-)

They also say:

====================================================================== NOTE: A damaged commutator may be resurfaced and undercut if facilities and skills are available to do so. However, it is recommended that any armature with commutator damage be replaced. ======================================================================

Good luck, DoN.

Reply to
DoN. Nichols

("DA12L-1600-A-1")

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Hi, William. I bet the Ebay listing said the unit was working when removed from service!

What you are looking at are called "slip rings" because, well, they are rings and the brushed slip on them. This is where the AC is picked up. Sometimes when brushes get really worn, they are so short they slip out of the holder bugger up the commutator or in your case, the slip rings. I suspect there are two brushes per slip ring because of the load sensing circuitry in the unit.

My very first suggestion is to find a distributor that has email capability and send them the picture for evaluation. Certainly you will need new brushes and the spring that is missing. Do you have a lathe that can swing the armature? If so, and you feel up to the job, disassemble the unit and turn and polish the rings yourself.

Personally, I believe, as you do, that someone opened up the unit and messed with it. The only reason that comes to mind is the automatic load sensing circuit board is bad and they attempted to repair it in the brush area. They didn't get it put back together correctly.

If you didn't pay much for the unit, a trip to a service shop is probably worth it.

Best regards, Paul

Reply to
co_farmer

snip------

Clare,

I'm curious about that statement. Aluminum oxide is not the recommended abrasive for non-ferrous materials, silicon carbide (emery) is. Is there something I don't know?

Harold

Reply to
Harold and Susan Vordos

As everyone else hs also pointed out, these are "slip rings." As I was reading your post, I could picture how a commutator would look after it ran with a spring crackling and arcing along the segments. It could be so bad even a lathe wouldn't clean it up. And the job of undercutting the insulators between the segments is very specialized.

But that's not your problem. If you can get the slip ring surfaces to clean up, using a file or the right abrasive paper (which is it?), the carbon brushes will make contact, and the thing should work. Of course, the best thing would be to take light cuts on a lathe. But if you are just hoping to get it working, and then make the next decision, you may not even have to disassemble it. It would be a shame to go to all the work and expense, and then find out there are shorted turns in the armature or something.

Reply to
Leo Lichtman

... carbon brushes i could see one was missing and the

This would be auction #290126346494, right? The one that says "works good"?

The first thing to do is contact the seller. Just 'cause he said "sold as is" doesn't let him off the hook for claiming it works good. Don't expect to get all your money & return shipping from him, but you should be able to get an adjustment. Get eBay involved if he isn't accommodating. Keep your feedback in reserve - he has spent almost 2 years getting 30 positives, so he should be sensitive about it. Above all, be sweet, but firm.

Bob

Reply to
Bob Engelhardt

You should be able to smooth out those marks with a "commutator dressing stone" The one I used to have years ago looked and felt sort of like a very hard rubber eraser with abrasive in it, but here's a fancier one:

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Course the rotor has to be spinning while you use them, but I'll leave that part up to you to figure out.

HTH,

Jeff

Reply to
Jeff Wisnia

Emery is electrically conductive - definitely NOT recommended in rotating electrical equipment of any kind.

Reply to
clare at snyder.on.ca

Emery is electrically conductive. NOT for use in rotating electrical equipment.

Reply to
clare at snyder.on.ca

Interesting. I can't imagine it's any more conductive than the swarf generated by any abrasive. I'd worry about the copper dust long before I'd let the silicon carbide be a worry, unless it was applied to an assembled device that's functioning. That might make sense. Seems to me that once cleaned, there should be no difference. Silicon carbide will do a noticeably better job on copper. Could be the concern is bridging the segments, creating a shorted commutator, eh?

Harold

Reply to
Harold and Susan Vordos

("DA12L-1600-A-1")

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I've seen brushes worn off past the ends, that leaves the spring to make contact with the commutator/slip ring which then gets chewed up. I've seen it happen a lot more with DC commutators than with slip rings, just because they're prone to more wear. The real solution is to put the thing in a lathe and clean up the rings with a few skim cuts, this will get rid of any possible eccentricity, too. I've had stuff from the factory be .030" out of concentricity, this just chews up brushes unless it's fixed. Just putting a file or some abrasive paper in there may clean up the surface but won't do anything if it's at all eccentric. Brushes, springs and holders should be available from the manufacturer if they're at all legit. It probably needs to be totally gone through, bits of spring and brush are likely to be where they shouldn't. The amount of material left on the rings needs to be looked at, too, might be there's not enough to turn off. Some of the cheap stuff really is.

On better quality machinery, the brushes have just enough lead that when the brush is worn to a nubbin, the spring comes up short on a flexible copper mesh tether and doesn't make contact with the surface. It quits working so at least the user has a clue that there's something wrong before damage occurs.

Stan

Reply to
stans4

Your unit has both a commutator and slip rings. You can see the two sets in the picture on the website. It is a motor/generator. The dc motor and ac generator are wound on a common shaft. The brushes with the segments are the ones for the DC motor. If the brushes have worn that much the commutator is probably running out of true. Do not! I repeat do not use the existing centers in the shaft to recut the commutator shaft unless you are absolutely sure that the center has not been damaged by a bearing puller or banged on with a hammer. You can check the center by putting a tenths dial on the shaft and see if you get any runout on the shaft with the shaft set on centers. If the shaft is running out the best way to cut the commutator is with a bearing installed on the shaft and the bearing held tight in a steady rest.

Reply to
john

Can't quote a reference but I remember NO Emery, Sandpaper only, to be the teaching when motors were repaired, not thrown away, 50 odd years ago.

-- John G.

Reply to
John G

Emory particles embed in the soft copper and wear the brushes.

Tom

Reply to
Tom M

You got it, Pontiac!! It was ALWAYS stressed NOT to use emery for ANYTHING electrical, particularly "rotating equipment". Emery will "embed" itself in the commitator slots, shorting the armature with spectacular results. (lots of bright sparks from the brushes)

Reply to
clare at snyder.on.ca

Some years ago, I was given an electric snow thrower by an electrician friend. He had received it from a neighbour who claimed to have repaired it once, himself. I gave it a quick try with no movement so started dismantling it. The evidence was right there, when Mr. Handy had taken it apart, he lost a brush spring which he promptly replaced with a piece of stretched out screen door spring ( about 16 gage wire). You can well imagine what happened to the commutator after the carbon brush wore out in the first five minutes of running. Gerry :-)} London, Canada

Reply to
Gerald Miller

("DA12L-1600-A-1")

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It looks small enough that if you have an auto electric shop that rebuilds starters and alternators they could turn down the rings. Avoid abrasives.

Reply to
beecrofter

In article , Harold and Susan Vordos wrote: :Interesting. I can't imagine it's any more conductive than the swarf :generated by any abrasive. I'd worry about the copper dust long before I'd :let the silicon carbide be a worry, unless it was applied to an assembled :device that's functioning. That might make sense. Seems to me that once :cleaned, there should be no difference. Silicon carbide will do a noticeably :better job on copper. Could be the concern is bridging the segments, :creating a shorted commutator, eh?

That's it, though I'd think the graphite dust from normal brush wear would be an even bigger concern. Perhaps the softer carbon and copper dust is less likely to become embedded in the separators. Whatever. The recommendation is never to use emery on a commutator.

Reply to
Robert Nichols

Bingo!

That's the reason---one I had overlooked. Silicon carbide is much harder than aluminum oxide.

Harold

Reply to
Harold and Susan Vordos

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