[T3] STUMPED!!???

Jim Adney jadney at vwtype3.org
Sun Nov 17 12:32:53 PST 2013


On 17 Nov 2013 at 14:15, Gary Forsmo wrote:

> >I can take it to physics one of these days and maybe
> >find where it has failed, but for now I've just marked it BAD.
> 
> Question?
> Is the rotor on our cars just a "pass-through" electrical device from the
> carbon brush to the brass(?) tip to carry the current to one of the 4 SP
> wires?  Or is there something internal of the rotor which could fail?

The correct rotors have a resistor in between. Those can sometimes go 
bad, but that's rare. Cheap replacements often skip the resistor.

> And, Jim, how will you test that "bad" Taiwanese rotor?
>  Dissection autopsy?  Carefully removing layers of the Bakelite material
> until you get to the internal elements?

There's a standard test for insulators which consists of using a high 
voltage spark generator. I would put the rotor on a grounded dist 
shaft then play the spark over the top of the rotor. The spark should 
travel evenly over the surface of the insulator. If there's a tiny 
flaw in the insulator, you'll see the spark go to that spot 
selectively. If it only goes straight to the top contacts, there must 
be a puncture internally. It's a rather easy and dramatic test.

I've also seen this test done on glass vacuum systems. The spark will 
find any invisible pinhole.

-- 
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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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