I have a requirement for both 12V DC system and a 24V DC system.
Is it possible to charge both from a single alternator? Or should I use a
Voltage Reducer to power my 12V load from my 24V batteries?

Thanks for your inputs!

I see no reason why a 24 volt alt could not be externally regulated to
produce 12v as an option on a switch, except for the catastrophic error
potential introduced.

This implies charge management by the skipper, and introduces
possibilities for errors that could prove dangerous, but which could be
managed by relays.

If you have more 2 or more 12 v batteries, you could wire 2 in series
and charge that from 24 v. This could cause charge imbalance if they
are not alternated as "tops" and not reconnected for 12v discharge in
parallel, or if not similar enough.

You would need to reconnect them to use both of them for 12v in
parallel, after stopping charging from 24 v.

Relays could be wired up to do this, and it was all discussed at length
about every 2 years ago.

Better to get one alternator each of each voltage and run the systems
seperately, sharing only ground and possibly a drive belt. Then you
would want 2 spares.

2- 12 alts could be connected so that one of them provides 24 v out,
but only if you can manage a non conductive mounting, or isolate the
12v output "ground" of the "top" alternator from it's case. It would be
possible therefore, to carry one spare that could replace either, if
one should fail, and charge maintenance could revert to an automatic
mode.

To evaluate the convenience factor, it would help to know the duties
and loads on the 2 voltage systems, i.e. 24 v starter and 12v house?
Or, do you have a 24 volt windlass or spotlight only?

It may be convenient to use a small 12 v generator in series with the
12v battery to charge the 24v battery, if it gets only occasional use.

most simply, a switched or relay setup could give you 24 v to start,
for an instance, and 12 v normally, with only a 12 v system and 2 or
more 12v batteries.

Possibilities abound!

Terry K

"Voltage Reducers" are not all that they might seem to be. Different sizes
are required for different loads. A miss rated size could damage a 12 V
item.

If I had the issue to deal with I'd install a 12V system in addition to the
existing 24 V system. A simple single wire 12V alternator only requires a
ground wire to the battery -, and the single positive lead to the battery
+. Mechanical mounting then becomes the only challenge.

If your engine's electrical system is 24V you can run the 12 V system dead
and still get home!

Don Dando


CyberSam wrote in message
news:BE9If.20846$0H1.15283@trnddc04...
I have a requirement for both 12V DC system and a 24V DC system.
Is it possible to charge both from a single alternator? Or should I use a
Voltage Reducer to power my 12V load from my 24V batteries?

Thanks for your inputs!

An interesting thought is that the difference between 12 and 24 volt
alternators may lie only in the installed regulators. Even a 12 volt
alternator produces open-circuit voltages on the order of 50-100 volts!
So maybe (and you would need to consult a specialist who rebuilds and
understands alternators to be sure) you can get by with only a 24 volt
alternator and a switch to charge the 12 and 24 volt systems. Each
system would need its own regulator, but that's nothing big, and the
switch would also switch the alternator field connection between the two
systems. Definitely don't want to turn those switches with the
alternator turning without some special protection.

Yeah, it's a kluge. But just about any 12/24 volt system is going to be
a design headache if it is to function properly.

Just something to think about.

Good luck.

Chuck



Don Dando wrote:
"Voltage Reducers" are not all that they might seem to be. Different sizes
are required for different loads. A miss rated size could damage a 12 V
item.

If I had the issue to deal with I'd install a 12V system in addition to the
existing 24 V system. A simple single wire 12V alternator only requires a
ground wire to the battery -, and the single positive lead to the battery
+. Mechanical mounting then becomes the only challenge.

If your engine's electrical system is 24V you can run the 12 V system dead
and still get home!

Don Dando


CyberSam wrote in message
news:BE9If.20846$0H1.15283@trnddc04...

I have a requirement for both 12V DC system and a 24V DC system.
Is it possible to charge both from a single alternator? Or should I use a
Voltage Reducer to power my 12V load from my 24V batteries?

Thanks for your inputs!

It's my impression that "start circuits;" i.e. the starter really doesn't
care about the voltage. Double the voltage and the no-load speed is
doubled, but under load it will pull the voltage down to whatever back EMF
corresponds to the starter speed. (The relays/contactors will have to have
the proper coil voltage, but that's a cheap conversion.)

Boats and electricals don't go together well at all. Simpler is more likely
to keep working.

Roger

http://home.insightbb.com/~derbyrm

"CyberSam" wrote in message
news:nAbIf.23932$Eq.3771@trnddc02...

The start circuit is 24V and the majority of the accessories will be 12V;
instruments, trim tabs, lights, radio, etc. I'd like to run a 24V
alternator
to charge a pair (in series) of 8D batteries. Ideally I'd like to have a
pair (in parallel) of deep cycle marine batteries for the 'house' load. I
realize now I may need to run two alternators, but I was just wondering if
a
single unit (that puts out both 12V and 24V) is available.

I think a second alternator, whilst it would involve some work in fitting
it, would be a better solution than a dual voltage alternator. Any such
arrangement is going to be either unusual or one-off, but 12V and 24V
alternators are very much off-the shelf items.
DF

"chuck" wrote in message
link.net...
An interesting thought is that the difference between 12 and 24 volt
alternators may lie only in the installed regulators. Even a 12 volt
alternator produces open-circuit voltages on the order of 50-100 volts! So
maybe (and you would need to consult a specialist who rebuilds and
understands alternators to be sure) you can get by with only a 24 volt
alternator and a switch to charge the 12 and 24 volt systems. Each system
would need its own regulator, but that's nothing big, and the switch would
also switch the alternator field connection between the two systems.
Definitely don't want to turn those switches with the alternator turning
without some special protection.

Yeah, it's a kluge. But just about any 12/24 volt system is going to be a
design headache if it is to function properly.

Just something to think about.

Good luck.

Chuck



Don Dando wrote:
"Voltage Reducers" are not all that they might seem to be. Different
sizes
are required for different loads. A miss rated size could damage a 12 V
item.

If I had the issue to deal with I'd install a 12V system in addition to
the
existing 24 V system. A simple single wire 12V alternator only requires
a
ground wire to the battery -, and the single positive lead to the
battery
+. Mechanical mounting then becomes the only challenge.

If your engine's electrical system is 24V you can run the 12 V system
dead
and still get home!

Don Dando


CyberSam wrote in message
news:BE9If.20846$0H1.15283@trnddc04...

I have a requirement for both 12V DC system and a 24V DC system.
Is it possible to charge both from a single alternator? Or should I use a
Voltage Reducer to power my 12V load from my 24V batteries?

Thanks for your inputs!

"David Flew" wrote in message
...
I think a second alternator, whilst it would involve some work in fitting
it, would be a better solution than a dual voltage alternator. Any such
arrangement is going to be either unusual or one-off, but 12V and 24V
alternators are very much off-the shelf items.
DF

Agreed. I'm going to look closely at my requirements. At this point I bet my
12V loads are too large for a Voltage Reducer. I'll likely just design two
separate systems, each charged with an independent alternator.

Thanks for the inputs.

I know this is an old thread, but there are devices to charge batteries from other batteries. "Sterling Power" in the UK have some, but I am sure there are others.