Subject: Re: excessive arcing brushes/commutator

From: [email-masked]
Date: Mon, 02 Dec 1996 04:20:57 GMT

On Fri, 29 Nov 1996 16:24:58 GMT, [email-masked] (Erich Mueller)
wrote:

>Hello,
>what are most probable causes for excessive arcing on the commutator 
>of an universal motor. Brushes seem long enough (not excessivelly worn
>yet) spring pressure looks ok. Rotor does not show visible damage of 
>windings. Commutator looks ok (no worn path of brushes or burnout of
>insulation between copper sections. 
>
>I speculate on shorted winding in rotor but can not prove / disprove 
>this assumption.
>
>Can you give me a hint?
>
>thanks
>erich
>
>
>-- 
>no Signature is a good Signature :-)
	I think that if you disassemble the motor you will find a ring
of solder inside the outer case.  Heat has melted the solder attaching
the armature windings to the commutator segments and it slings outward
and collects in the stator housing.  This can usually be fixed by
resoldering the wires.  The biggest problem you will have is getting
the wire and the slot clean enough to take solder due to the arcing
that has occured creating a surface on the copper that will not
readily tin.  Careful scraping and the use of a fairly agressive
solder flux usually works.  Try not to use acid core if you can avoid
it.
	Good luck-----jhale

---

From: [email-masked] (Bill Webster)
Date: Mon, 02 Dec 1996 08:02:42 -0500

In article <[email-masked]>, [email-masked] (Erich Mueller)
wrote:

> of an universal motor.
(snip)
> I speculate on shorted winding in rotor but can not prove / disprove 

How are the bearings (if there are any)?  If they are worn, the output
shaft will vibrate and this can cause the brushes to bounce, thus causing
arcing.

Has the load changed?  Excessive loading will also cause more than usual arcing.

Does the arcing go away (or reduce) when the motor has no load?

Short circuits on the rotor are not easy to detect with 'common' home test
gear.  You could take the motor to a service center (like Sears, or a car
garage that repairs starter motors/alternators) and ask for a growler
test.  This is used to find shorted windings.

Best of luck with the repair.

regards.

-- 
Bill Webster   [email-masked]