> A peak of only 140V is not sufficient for an arc across any switch
> designed for even 12V.
Sure it is, if the contacts are close enough together at the instant. Open
circuit on an arc welder is only 30-40 volts.
> The only electronics that would be affected by a
> properly wired straight disconnect would be those on the alternator side
> of the switch, which should be only the regulator and the rectifiers.
> Certainly there is no problem with having a switch that connects a
> resistor before opening the circuit, but it sounds very
> belt-and-suspenders to me.
No argument there.
> You also might be better off with a large
> capacitor (something in the range of 1uf at 480V) than a resistor, since
> it would be open circuit to steady DC and would be unlikely to present a
> hard-to-diagnose switch or wiring failure. You wouldn't't even have to
> have a make-before-break switch to use it. It might be what they use
> internally to limit transient voltage, though a high voltage zener is more
> likely.
For the alternators I've had apart, there is nothing internally to limit
transient voltages, except for blowing diodes. In fact, most of them will
happily generate 120vdc all day with the regulator disabled. This used to
be a popular modification, before gen sets and battery powered tools became
common, as many 120vac tools and lights will run on 120vdc.
I've even seen articles on using a big truck alternator as a welding source;
although I've also heard it's apt to pop diodes.
Randall
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