Thanks to everyone who's contributed ideas to this thread.

It's my understanding of alternator operation that the voltage is
"built-in" by the number of poles, the number of turns on the rotor/stator,
and least of all by the regulator.
The speed controls current, not voltage.

If the regulator is removed (or the reg.'s ability to reduce the field
current is removed), then the alternator voltage will rise to over 100 V.
(OK for US -
you could get mains power straight from output - either AC or DC, at a high
frequency,
but I need 240VAC in Oz.) I believe a large alternator [200A] might produce
around 7200 Watts when driven this way. It would probably need 2 belts and
12 HP to drive it at this level, assuming bearings, heat, diodes, etc. were
upgraded.

What I want to do is charge a bank of solar batteries at up to a C20 rate
(about 40A in my case), with a 24V alternator driven by a 3- 6HP stationary
engine, with an adjustable regulator circuit that will provide up to 30VDC
and taper the charge as the batteries fill.

Great booklet about alternators :
http://www.1stconnect.com/anozira/Si...alternator.htm

cheers all,

Marcus in Oz @ 28.4VDC (Sunny day!)