On Thu, 14 Jul 2005 01:41:13 UTC Jerry Bransford >
wrote:

> How can the alternator even work with the battery gone? Generators work
> fine with no battery, alternators do not since they need +12 volts from
> the battery for the exciter voltage before they will work.
>
> Jerry
>
> Mike Romain wrote:
> > Now you are talking a dead computer because it got fried from the
> > alternator surging with no battery buffer.
> >
> > Mike
> > 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> > 88 Cherokee 235 BFG AT's
> >
> > curbrider wrote:
> >
> >>91 jeep cherokee 4.0 replaced alternator and it over charge even with the
> >>battery disconneted

There is enough residual flux to self excite most alternators - but
I've only seen one that would avalanche (or bootstrap) enough current
to actually be functional. Once excited, it's another story - the
alternator needs on the order of a couple of amps in the rotor to
produce full output so if you keep the battery on long enough to get
past a certain point (and it doesn't take much) then disconnect it,
the alternator will continue to operate at up to near rated output
until it is shut down in some way (stopped, etc.). The ones I've
played with have had miserable regulation and horendously noisy
outputs, but they do work. A few even got so far out that they
exceeded the voltage ratings for their diodes and fried them.

--
Will Honea