AC electromotor. Brushes burning.

[vlad777]

Hi. I have borhammer that is malfunctioning.
When put in operation motor turns slowely and
brushes are burning and a lot of smoke comes out.
Rotor is not jammed.

Both rotor(with collector) and stator are (of course) electromagnets.
Visually inspected they dont seem to be burned out.

I didnt have my multimer with me.
When disassembled stator connected to 220V does not heat up.
Can I do the same test with the rotor?

Any suggestions?

Many thanks.

 

[Hero999]

It sounds like there's a shorted turn.

If it's on the stator, it should be fairly easy to rewind.

If it's on the armature, then you need a new armature.

I take it you've looked at replacing the motor?

 

[vlad777]

I take it you've looked at replacing the motor?

I doubt I can find replacement parts and it might not be
cheap enough.

 

[bychon]

I believe the armature is shorted and the escaped smoke can not be re-installed. With no replacement parts and no money, this is a dead motor.

 

[Hero999]

Is it parallel or series wound?

If it's series, did you short the brushes when connecting the stator to the mains?

I'm trying to think now whether just connecting the stator to the mains will cause it to overheat or not, even if it's healthy.

I think it will overheat if it's series wound because it's not designed to have the full mains voltage across it but if it's parallel wound it should be fine.

 

[Vizier87]

how 'bout some pictures? That might help.

 

[vlad777]

Is it parallel or series wound?

I believe its parallel because there was a spark every time i would connect
disasm stator to mains and also I think that brushes are connected to the
same two contacts as is stator.

 

[vlad777]

how 'bout some pictures? That might help.

For the pictures you would might have to wait for about a week
because I forgot to bring it with me.

 

[shortbus=]

What condition are the brushes in ? when brushes get too short(worn out) they don't make good enough contact with armature.
That will cause overheating, sparking, and if they are short enough to "cant"(angle in brush holder) that can cause the two poles to be energized at the same time. Even when to the eye they look long enough the may not have enough spring pressure to seat correctly.

 

[Reloadron]

How do the brushes look? Still plenty of length? Good downward force on them?

Ron

 

[Hero999]

It sounds like the armature (rotor) has a shorted turn, in which case it needs replacing, assuming you can find a spare.

Have to checked the commutator (the bit the brushes make contact with) for debris shorting the contacts?

If it's clean and the brushes are fine then it must be a shorted turn.

As you've said, the stator is fine because you've connected it to the mains and it didn't overheat or smoke.

 

[vlad777]

I did clean the commutator and the brushes were fine but few tests of a few seconds
pretty much destroyed them.
It seems that Hero999 is correct to say that rotor is fryed.

Can you tell me how to test the rotor?

 

[Nigel Goodwin]

I did clean the commutator and the brushes were fine but few tests of a few seconds
pretty much destroyed them.
It seems that Hero999 is correct to say that rotor is fryed.

Can you tell me how to test the rotor?

You already have - as already suggested, the rotor has shorted turns, that in turn causes the brushes to burn up instantly.

 

[vlad777]

Does this look burned to you?
But it does measure neer zero resistance on multimer.

On the other hand the spark when I tested the stator
most likely came because of the parallel capacitor 0.22uF
and I cant get a reading when I try to measure the
resistance of the stator.

So if stator wire is somewhere cut (burned out),
I mean if the stator is not conducting is it
possible for the rotor to spin?

And I am also trying to think how does the magnetic field
of the stator affects the rotors inductance.
Does it increase or decrease it, because if it
increases it than the motor would work fine
if the stator is fine.

Edit: Power consumption sayes: 850 Watts

 

[Hero999]

The rotor looks good but it's difficult to tell just from a picture.

The rotor will measure near zero whether it has a shorted turn or not.

The stator should also have a pretty low DC resistance.

I wouldn't expect the rotor to turn at all if the stator has gone open circuit, especially on a AC motor.

I suppose the rotor might be turning because the brushes have been worn so they act as a weak ratchet making it easier to turn in one direction than the other.

The rotor will soon overheat if it's left connected without the stator working.

It's probably only one of the stator coils which has gone open circuit, once you find out which one it is, you can rewind it.