Why 28V DC?

On Sun, 18 Jan 2004 19:20:48 -0500, "Ron Natalie"
wrote:

"Jim Weir" wrote in message news
Jeez...that's something I've never considered. You are RIGHT, internal to that
alternator there IS 3-phase AC that is regulated and rectified to produce the
DC...

And now with three small transformers and a little surgery on the alternator, we
could have 3-phase 115VAC to run those military gyros...I wonder...yeah, I know
the frequency is a function of engine RPM...but still...
\
You think that AC coming out of those inverters is all that stable? It tends to wander
with the input voltage. Of course the real problem is that if the alternator crumps, the
battery will not put out three phase.

The voltage is pretty stable, and is a square wave clipped by the
battery voltage ... at least while charging. I think the regulator
shuts it off when not, but am not sure. Years ago, when construction
of auto alternators was less optimized, I helped a freind rig his full
kW ham rig ... we took the alternator output into a 3 phase
transformer to get plate voltage. MUCH better than the vibrators of
the day. And we needed very little filtration with the 3 rectified
phase.

FYI, one, and perhaps the main, advantage of 3 phase rotating
machinery is that in theory, the developed torque of a motor, and load
torque of a generator is constant. Only manufacturing tolerances and
real conductors and iron give ripple.