Re: Diodes Part 2

[david crooks <david.crooks@xxxxxxxxxxxx>]

>You can run one of these Motorola alternators
>without the isolation diode but it is like
>replacing a fuse with a slug.

True, but I'll return to this in a second...

>The diode ... is there to protect the internal
>diodes which are much harder to replace.  Clip
>your jumper cables on backwards and the isolation
>diode may go, but the circuit to the internal
>diodes should then be open and protected.

Sorry but this is completely wrong.
The isolation diode will provide no protection
against reversed jumper cables, it allows current
to flow in the same direction as the rectification
diode pack.  It's purely the luck of the draw as
to which diodes blow first, and the smaller diodes
in the rectifier pack are more likely to go first.

The isolation diodes purpose is to remove the alternator
and regulator from the electrical circuit when the
alternator generating any voltage.  This used to be
done with a cutout relay, but the diode solution is
simpler and much more robust.  Your alternator will
work fine without it, but you'll see two side affects.
First your charging voltage will by about 0.7 volts
higher, which is what would normally be lost across
the diode.  Secondly it eliminates battery charge
leakage through the alternator when it's not running.
In other words remove it, and you'll find your battery
going flat more often...

Cheers,

Dave