From: "Andy Dingley <dingbat@codesmiths.com>" <dingbat@codesmiths.com>
Newsgroups: rec.autos.tech
Subject: Re: Alternator ? (Excessive Voltage)
Date: 6 Dec 2006 12:23:54 -0800
Message-ID: <1165436634.803374.175660@79g2000cws.googlegroups.com>

Doc Holliday wrote:
> Just for future reference does anybody have the answer to this one.

Most likely the regulator went batshit. It stick full voltage across
the alternator field windings (the rotor) and the output voltage goes
high.  It only gets to 16V, not higher, because the magentic core in
the rotor saturates, no matter how much extra current you push through
it.

Doing this deliberately is a "get you home" fix if your regulator dies.
But keep the revs down!

It's definitely not the output diodes. Regulator faults may put the
output voltage up or down, but diode faults always put it down.

It _might_ not be the regulator. If it's a battery-sensed alternator,
then a broken sense wire from battery to regulator can cause this same
fault. Some older cars (particularly with Lucas ACR alternators) can
suffer this if the dashboard charge warning bulb has blown, is missing,
or has been replaced by one of the wrong rating.

It's also possible, on a machine-sensed regulator that the third set of
diodes used to feed the regulator (paralleled to the positive output
diodes) might have failed. This is rare though - the high-power output
diodes generally fail long before these little ones.

From: "Andy Dingley <dingbat@codesmiths.com>" <dingbat@codesmiths.com>
Newsgroups: rec.autos.tech
Subject: Re: Alternator ? (Excessive Voltage)
Date: 7 Dec 2006 07:40:39 -0800
Message-ID: <1165506039.348906.266610@n67g2000cwd.googlegroups.com>

Scott Dorsey wrote:

> >It only gets to 16V, not higher, because the magentic core in
> >the rotor saturates, no matter how much extra current you push through
> >it.
>
> Now, I remember some trickery out there that allowed you to get 200V
> or so off an automotive alternator, with some trickery to get a high
> voltage on the field coil, but without rewinding anything.

I've never heard of 200V, but you can certainly hit 50-ish.  The trick
is to use an old heavy alterrnator that simply has a bigger core, then
to spin it faster by fitting a smaller pulley.