> Most modern-day electronics are designed to handle reasonable
> faults--losing power suddenly is certainly a reasonable fault. Really all
> you need is to open the output wire of the alternator and open the battery
> circuit. You can do that with any of the cutout switches that have a heavy
> pole for the battery disconnect, and a second lighter pole for the
> alternator disconnect.
>
> You won't get a power spike delivered to the electronics from the
> alternator if it's disconnected. You might get a higher voltage delivered
> to the internal regulator of a one-wire alternator, but that's what it's
> there for and they can handle it.
Bill, I beg to differ. All modern manufacturers warn against doing this
very thing, because if the alternator is running at full output, the
regulator cannot shut it down fast enough to avoid a very large voltage
spike. Even with no current through the winding, the magnetic field in the
rotor takes time to decay. And, if the regulator does fail, the output
voltage can potentially rise to lethal levels, more than enough to arc
across the just-opening contacts in the kill switch and fry that expensive
computer.
Of course, one very rarely operates the cut-off with the alternator at full
output; and generally when that does happen, preserving the electronics is
not the primary concern. So, you may get away with it for a long time and
never have a problem. But Steve's idea of shutting down the alternator
(with a "make before break" switch) is sound practice.
Here's a switch I found on the Internet just now.
http://www.racerwholesale.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=R
W&Product_Code=ELE-28606
If you can't cut&paste that link together, go to
http://www.racerwholesale.com
click on "Battery cutoffs" on the left and then "Battery Cut-Off switch -
Alternator kill" P/N ELE-28606
NFI, not even a customer, just something I found on the web.
Randall
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