Motor is eating Brushes

[M@tt]

after a bit of advice

I got a Clarke abrasive chop saw from someone off here must have been a year or so ago for free as it wasn't working. Anyway i've finally got round to having a look at it.

i managed to get it running but something's not right. The brushes were sparking like mad and they basically wore themselves down to practically nothing within a minute or so!!

I did a visual check on the wiring and i can't see anything obviously wrong

Any suggestions as to what could be causing this?

 

[rtbcomp]

Could be worm/shorted commutator or shorted turns in the armature.

 

[brightspark]

one of the windings and a segment on armature probably burnt out and loose causing burning on the brushes. the armatures probably us

 

[wotwot]

Had the same probs with mine only 18 months old,very light use but it was A B&Q special,and no longer available,comutator duff and no one does repairs in our chuck away world.
Sorry couldnt find out how to post photos, I have some on photobucket from when I was trying to fix mine.

 

[pedrobedro]

I had an angle grinder doing the same. I stripped it down and held the commutator in one hand with some 2000 grit emery round it and spun it then cleaned the slots out with a piece of hacksaw blade and it's worked fine now for a couple of years.

 

[Betelgeuse]

if its eating brushes, shouldn't you be feeding it something more wholesome ?
try carrots or cabbage !
(sorry, couldn't resist!)

 

[brightspark]

if its eating brushes, shouldn't you be feeding it something more wholesome ?
try carrots or cabbage !
(sorry, couldn't resist!)

its all ready cabbaged

 

[PTvor]

I had an angle grinder doing the same. I stripped it down and held the commutator in one hand with some 2000 grit emery round it and spun it then cleaned the slots out with a piece of hacksaw blade and it's worked fine now for a couple of years.

Definitely worth a try. The usual advice is to use sandpaper, not emery, for cleaning commutators.

However, as others have said, the windings are probably shot and the motor is a write-off.

 

[M@tt]

cheers chaps

is there any tests i can do to determine what the problem is? ie check continuity across stuff?

electrics is not my strong point

 

[the snooper]

The usual advice is to use sandpaper, not emery, for cleaning commutators.

the proper way is to use a commutator stick

if youve not heard of one before look here

 

[Ducati]

cheers chaps

is there any tests i can do to determine what the problem is? ie check continuity across stuff?

electrics is not my strong point

Do you have anyone local who either repairs engine starter motors or repairs electric motors, if so they may well have a ' growler ' .

It is used to test armatures, they may test yours for the price of a pint.

 

[Wedg1e]

I usually use a fibreglass pencil to clean commutators - if they're really bad then a Loyblock works wonders but you have to shift the grit afterwards.

 

[GeorgiePorgie]

Is there any play on the shafts bearings? bound to be if its a Clarkey?

 

[wotwot]

This was mine after just a few seconds, Kept been told by the other forum the brushes were worn badly.
Kept telling them it may be the comutator as the brushes were still long enough.

http://http://www.mig-welding.co.uk/forum/attachment.php?attachmentid=24584&stc=1&d=1320052385[/IMG]

http://http://www.mig-welding.co.uk/forum/attachment.php?attachmentid=24585&stc=1&d=1320052385[/IMG]

 

[M@tt]

theres no play in the bearings (suprisingly ) and i did give the surface of the commutator a clean with some sand paper but to no avail.

Unfortunately i dont know anywhere that does motors and would struggle to get anywhere in the week for someone to take a look at it hence wanting to know if its something i could perform myself with a multimeter just to confirm whether its scrap or not

 

[PTvor]

Have a look with google for motor testing with multimeter. You might find a site with diagrams and a clear description.

I found this

http://www.tpub.com/content/construction/14259/css/14259_299.htm

As I recall, you can check for open circuit - broken - windings, and you can check for shorts between windings and to earth, but it's a fiddly business doing it across the commutator.

It's my observation that with small motors, if you can't get them working by cleaning up the commutator, checking the brushes and looking for loose connections, about half an hour to an hour's work, then you may as well scrap them.

If the brushes have been replaced with the wrong grade for the motor, they can wear out very fast.

I suppose you could find someone to rewind the motor, but I'd guess it would cost more than buying a better saw new.

 

[GeorgiePorgie]

theres no play in the bearings (suprisingly ) and i did give the surface of the commutator a clean with some sand paper but to no avail.

Well I guess the problem stems to why it was given to you freely.

 

[M@tt]

so is it the small gaps between the contact faces that the brushes touch that need cleaning up? (as well as the faces themselves)

so if i put my multimeter to continuity check and touched one of the contact sections with one probe, then diametrically opposite there should be presumably be another contact section which it should bell out to. If theres more than 1 section then presumably that would indicate a short?

 

[eddie49]

[ The pictures posted by wotwot show burnt commutator bars, and overheating where the winding is spotwelded to the bar. That is a shorted winding, and a U/S motor.]
The commutator faces should be reasonably clean and bright, and the gaps between the copper bars should be free of carbon dust. A winding coil can go open-circuit, short to earth ( i.e. the iron laminations of the armature ), or short to another coil. A so-called "Growler" is the only way to test. I've never succeeded with a multimeter - and in a way it is pointless anyway. As others have said, excessive sparking with a clean commutator and brushes of a reasonable length means shorted winding(s) and thus a duff motor. Due to the high speed and high operating temperature of modern power tool motors, the windings are epoxied into place, and they cannot realistically be rewound.

 

[pedrobedro]

Definitely worth a try. The usual advice is to use sandpaper, not emery, for cleaning commutators.

However, as others have said, the windings are probably shot and the motor is a write-off.

Sorry it's just my terminology, it's called emery if it has grit on it. Most likely it was al-ox paper which is probably wrong as well but it is still working after two years of use so I'm not going to take it to bits to do it with the right stuff It might be worth asking if it can be repaired as I did it with a circular saw ages ago and it was repaired for £35 with a years warranty on the repair.