On Sat, 21 Apr 2007 21:49:14 +1000, "marcus" wrote:

Has anyone come across a circuit for a manually-adjustable, or even
automatic regulator circuit
to control a 24V car alternator?
Application is deep-cycle solar battery charging using 3-5HP small petrol
motor coupled to 24V alternator.
Need to tweak the voltage up to about 29-30V to equalise the batteries.
Solar batteries like a 3-stage charging regime - boost, bulk & float. These
voltages are all diff. and also depend on battery type (chemistry), so the
field needs to have these adjustable set-points.
Would be nice to be able to sense battery voltage and feedback into
alternator field voltage, to make a set-and-forget circuit.

Here's some background (12V, and no feedback) :
http://www.homepower.com/files/mark8.pdf

Thanks to everyone in aus.electronics who had a look at this.

Jim Thompson : I notice from your web pages that you have designed some car
alternator regulation projects - wondering if you have any thoughts?

Thanks all

Marcus in outback Oz

I couldn't see the file you reference.
but
12 volt alternators can put out 14 volts at idle so with just a pulley
adjustment or running them faster the voltage goes up proportionately.
From that point on it is just a matter of a regulator.

I have a two transistor regulator that I scrounged from a Chilton's
manual back in '72. They didn't show component values, but I put what
I thought would work and it did in a BMW motorcycle and Toyota Land
Cruiser. Doesn't do anything fancy like float at a lower voltage, but
I could post the schematic if you want or email it.

Very simple device - NPN pass transistor is biased "on" with a
resistor (turning on the rotor) and a second transistor turns it off
when the Zener/ and potentiometer-setting voltage is exceeded. The
Chilton's manual showed fixed resistors - I used a military spec wire
wound pot to set the voltage.

The BMW reg was in the bike for 10 years (in the weather) and I had no
problems with it other than painting the transistors so the TO66 cases
wouldn't rust through - on the land cruiser I used a 2N3055 and it
never rusted in the engine compartment. No heatsink was needed - the
rotor would pull about 3 amps maximum.
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