On Apr 23, 10:38 pm, "marcus" wrote:
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.

No, this is not correct. The open circuit voltage is given by the
rate of change in magnetic field the stator sees. This means that it
varies with the RPM.

On Tue, 24 Apr 2007 15:38:59 +1000, "marcus" put finger
to keyboard and composed:

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!)

Can you relax your requirement to just a current limited 40A, 28.4VDC
constant voltage regulator? If so, then the required circuit would be
extremely simple, ie a 40A 600mV current shunt, 3 or 4 transistors, a
few diodes and a few resistors. The current limiting circuit (one
shunt and one transistor) would ensure that the current never exceeded
40A, even at low states of charge.

Temperature compensation could also be provided by a string of 1N4148
diodes.

If you are happy with this, then I will draw up a circuit for you.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Frank ~
Thanks for your offer of a circuit - can I take you up on that?

thanks

Marcus, in the rain!! (first time in about 3 months....)

On Apr 24, 10:58 am, MooseFET wrote:
On Apr 23, 10:38 pm, "marcus" wrote:

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.

No, this is not correct. The open circuit voltage is given by the
rate of change in magnetic field the stator sees. This means that it
varies with the RPM.

....and, it varies with the field current.

Terry k

On Fri, 27 Apr 2007 09:51:01 +1000, "marcus" put finger
to keyboard and composed:

Frank ~
Thanks for your offer of a circuit - can I take you up on that?

thanks

Marcus, in the rain!! (first time in about 3 months....)

This is the basic idea:
http://www.users.on.net/~fzabkar/alt-reg.JPG

If you have a grounded field alternator, then the field section of the
circuit needs to be modified. You also need to know the battery's
temperature coefficient before you can select your string of diodes.
Silicon diodes have a tempco of -2mV/degC, but zeners can have either
positive or negative tempcos that depend on the zener voltage. IIRC,
zener tempco is zero at around 5 or 6V. An alternative place to put
the signal diodes would be in the voltage divider.

I have added a momentary start switch just in case the residual
magnetism in the rotor is insufficient to self excite the alternator.
I have avoided using the "charge" lamp that normally provides this
function because the batteries would slowly discharge through it if
the motor were to stop.

One other thing you might like to consider is an overvoltage monitor
that trips a contactor if the regulator fails.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

On Apr 27, 8:33 pm, Franc Zabkar wrote:
On Fri, 27 Apr 2007 09:51:01 +1000, "marcus" put finger
to keyboard and composed:

Frank ~
Thanks for your offer of a circuit - can I take you up on that?

thanks

Marcus, in the rain!! (first time in about 3 months....)

This is the basic idea:http://www.users.on.net/~fzabkar/alt-reg.JPG

If you have a grounded field alternator, then the field section of the
circuit needs to be modified. You also need to know the battery's
temperature coefficient before you can select your string of diodes.
Silicon diodes have a tempco of -2mV/degC, but zeners can have either
positive or negative tempcos that depend on the zener voltage. IIRC,
zener tempco is zero at around 5 or 6V. An alternative place to put
the signal diodes would be in the voltage divider.

I have added a momentary start switch just in case the residual
magnetism in the rotor is insufficient to self excite the alternator.
I have avoided using the "charge" lamp that normally provides this
function because the batteries would slowly discharge through it if
the motor were to stop.

One other thing you might like to consider is an overvoltage monitor
that trips a contactor if the regulator fails.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

http://homepage.sunrise.ch/mysunrise...ot/voltreg.htm