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Author Topic: cleaning alternator sliprings - suitable abrasive?  (Read 1277 times)
marcus
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« on: April 08, 2018, 09:03:10 PM »

Hi all,

I've got an alternator that's working intermittently - brushes & springs seem fine but they are not making consistent contact as the shaft rotates so I was going to try and clean the rings a bit. I've always used glasspaper for sliprings and commutators as I read (a long time ago - possibly in a morris minor haynes manual) that you should use glass as opposed to sand, emery,wetndry, etc as the other abrasives stick in the copper and turn it into an abrasive surface.

My problem is that I seem to have lost my last scrap of glasspaper and I can't seem to find it in the local shops, and online it takes me to 'glasspaper/sandpaper' that on close inspection turns out to be common Al oxide.

can I still get glasspaper? and if not does anyone have an idea what abrasives are OK to use  instead?

Thx.
Of course, it might all go for naught as modern alternator rings are made of very thin metal and it may turn out to already be worn through when I try to clean them...
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oliver90owner
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« Reply #1 on: April 08, 2018, 09:57:10 PM »

 If they are that rough, change the slip rings.  Might as well while you have it apart.

Usual fault is with the brushes sticking.   Outer brush normally wears faster than the centre brush, so the trick was to swap them round, rather than hunting round for a new set.

Drive end bearing is another part to change, while you are at it.  They can cause rough running, too.  Iíve rarely changed a commutator end bearing, but the seals can leak and the bearing run ndry.
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Countrypaul
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« Reply #2 on: April 08, 2018, 10:42:03 PM »

Intrestingly, Wikipedia implies sandpaper and glasspaper are the same thing and neither sand nor glass are normally used! Since glass is made from sand it may be that there was very little difference if any. It could also be that differnt manufacturers used different names for the same thing and the author "fell for a line" if it was very old.

For cleaning metal contacts, especially those gold ones at the edge of older computer boards, I was always told to use a hard eraser those used for pens rather than pencil, they used to come with a blue end (hard) and a normal pink end (soft) - might be worth trying on the rings. Ive cetainly used it on model railway tracks  whistlie
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marcus
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« Reply #3 on: April 08, 2018, 11:23:10 PM »

Aha! I hadn't considered the possibility of getting replacement rings - I'll look into that... I had expected the fault to be sticking brushes as it had been working intermittently - but they move freely and are both still long.

CP certainly it seems to be true that sand/ and glass paper are now generic terms used for aluminum oxide abrasive, but glass paper definitely used to be available as I have bought it in the past, and it really did appear to be, essentially, graded glass fragments stuck on paper. Might as well give the eraser a go - but if I can source replacement rings then I'll probably end up doing that.

Thanks very much
M
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Nickel2
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« Reply #4 on: April 09, 2018, 09:26:31 AM »

If the rings aren't too scored, maybe try 'Garryflex' polishing block. They are available in 4 grades for about a fiver each. The finest would probably suit your purpose. Like CountryPaul says, try model railway shop for track cleaning rubber block. Maplins does one for £1.50; as they are closing down you may get one cheaper.
N2
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Philip R
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« Reply #5 on: April 09, 2018, 02:58:45 PM »

Marcus,
Are the sliprings round or have they developped a flat spot. Abrading the suface will not help if the brushes are bouncing on the slipring surface.

Without a dial gauge, I appreciate this is difficult to ascertain.

With the sparkplug removed, turn the engine fan manually, and see or feel if the brush is moving in its brushholder.

When I was responsible in the past for two large alternators with exciter and main brushgear fitted, we used to have problems with brushgear sprking eroding the slipring surface. Polished with silicon carbide crocus paper on the back of a scaffold board, ( Machine shut down and on electric turning gear with a little bit of steam to speed up the shaft). Otherwise it was remove the brushgear and set up a portable in situ lathe and machine the rings back to roundness.

Philip R
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marcus
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« Reply #6 on: April 09, 2018, 11:19:41 PM »

I do have a rubbery abrasive block - can't remember it's make but not Garyflex. But I am getting the impression that the general view is that i shouldn't worry too much about the type of abrasive material I use (though I will try the hard eraser first), just use fine grade, lighty holding the abrasive and spinning the rings.

AFAIK the rings are round - but I haven't checked- I didn't know they could develop flat spots. Something is causing the high impedance at one point when rotating by hand, I suppose it could be a flat spot; there is a section of one ring that looks very slightly darker than the rest - possibly caused by arcing? - I could mount it up on the lathe if I have to, but getting it turning concentric may tax my lathe skills - I may have to invest in a dial gauge, and I doubt there's enough metal to allow for any mistakes.
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Heinz
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« Reply #7 on: April 14, 2018, 07:17:15 PM »

Scotchbrite pads are ideal for cleaning slip rings and similar, takes the muck off without removing metal or making the surface rough. Either buy from a car parts place or use the green part of a washing up sponge.
Be sure to lift the brushes off the slip ring afterwards and blow any loose grit/muck/green bits out afterwards.

H
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"Do, or do not. There is no 'try' "  Yoda
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