[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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