On Thu, 25 Oct 2012 09:54:41 +0100, "Dave Plowman (News)"
wrote:

In article
,
harry wrote:
I looked into it and found a web page about alternators with external
diodes for use in light aircraft. Apparently flicking off one of the
isolators (battery I think) required in an aircraft would wreck the
diodes in a conventional alternator.

With the engine running?


The battery isolator in light aircraft is so the battery can be
swiftly cut off if there is an accident to prevent fire.

Whatever. If you disconnect the alternator from the battery with the
engine running, there's a very good chance of damaging the alternator as
the output volts can go sky high if there's little load. And that high
voltage can kill diodes.

Hence why they are wired like this in competition vehicles.

http://www.holden.co.uk/productImagesWD/020_011.jpg

The main heavy duty contacts open on isolation to kill the battery feed,
simultaneously a pair of NO contacts close to shunt the alternator output via a
resistor to earth and a pair of NC contacts opens to kill the ignition feed.







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