On Fri, 31 Dec 2004 00:52:30 GMT, Lancer wrote in
:

snip
I still don't quite see why you would need to have the alternators run in
phase. If you were taking the 3 phase out before rectifying it, yes.


The problem is if they slip out of phase then the ripple from each
will be mixed. At 60 degrees shift the ripple between the two will be
twice that of one alternator. That can't be good for a battery. Also,
as the alternators continue to rotate against each other the output
will change from very smooth to twice as bumpy, and will do so at a
very low frequency. The problem here lies with how the regulator
senses the DC output. It's doubtful that the regulator will see true
RMS, so the result is that you will get a low frequency variation of
the DC output. Another problem is how that variation will be fed back
to the rotors from the regulator..... but that's all moot:

I did a little research and found out that only a few alternators have
regulation fast enough to smooth the ripple. That's good news because
there is no need to use a single regulator or to lock the phase of the
alternators. All that's needed is current equalization with resistors.

And for the sake of mentioning it, I also found out that most of the
newer alternators (like the Delco CS130 in my truck) use a 'switching'
type regulation scheme, which may be why alternator whine in the radio
is becoming much more common.