Using a 12vdc Alternator to Charge a 24vdc Battery Bank

[Marqus]

Originally Posted by goboatingnow

That simply will not work. Dave

May well be true Dave, but Fuss (OP), myself and some here would probably appreciate it if you could say what you think WOULD in fact happen if the alternator is so connected - i.e. sense wire to 12v point and main output to 24v point (other than possible rise in temperature)?

[Andina Marie]

Better (and cheaper) than the 12 to 24 volt converter is to charge them in parallel using a Trollbridge24. It automates the 12/24 volt switching.

[Seahunter]

You can use an electronic (digital) or electromechanical (solenoid) combiner as there are many on the market. You can find the solenoid type (big but work the best) in a commercial truck/bus wrecking yard. Combiners put no extra load on the alternator.

[Andina Marie]

Originally Posted by Seahunter

You can use an electronic (digital) or electromechanical (solenoid) combiner as there are many on the market. You can find the solenoid type (big but work the best) in a commercial truck/bus wrecking yard. Combiners put no extra load on the alternator.

A Combiner is not going to charge a 24 volt battery from a 12 volt alternator.
I'm fairly sure the original idea of putting the sense wire on the 12 volt tap will work fine. During the bulk charge stage when the alternator is putting out maximum it is in a "constant current" mode so the current is a function of the load voltage which will be 24 volts instead of 12. This should limit the load to a safe value. Fairly easy to test, just measure the current when you first start it up, it won't overheat in 30 seconds.

[FlyingCloud1937]

If you're really interested in doing this follow this link and read all about it

http://www.microcogen.info/index.php?PHPSESSID=t27gpdebsrbkvb9fm7je738a95&top ic=157.msg1359#msg1359

I know the fellow that wrote this white paper, and the system has been thoughtfully tested and confirmed.

Lloyd

[Seahunter]

Originally Posted by Andina Marie

A Combiner is not going to charge a 24 volt battery from a 12 volt alternator.
I'm fairly sure the original idea of putting the sense wire on the 12 volt tap will work fine.

We use combiners all the time for this type of charging system (all 12v batteries with combined parallel and series together). If you're employing a "24v battery" as opposed or even to/or a 24V bank then you want to be using a Balmar Duo Charge or something like.

[Andina Marie]

I think you posted in the wrong thread, Seahunter, look at the TITLE. "Charging 24 volt battery from a 12 volt source." The only combiner I've seen that can do this is the Trollbridge24 frequently used by Bass fishermen to charge their 24 volt trolling motors from a 12 volt outboard.

[hellosailor]

From the manufacturer's own web site, the Trollbridge 24 allows you to charge two 12-volt batteries from a 12-volt source, and then combine the two 12-volt batteries into one 24-volt bank to power a 24v trolling motor.

It does not "charge" anything at 24 volts. It does not "charge" a motor at all.

The charging and the motor powering are two totally separate operations and configurations and it looks like you won't be charging anything while using the 24-volt output for the motor running. Motor, not 24v battery.

It is just switching the 12-volt batteries in and out of series/parallel array to make the battery bank supply 24-volts instead of twelve.

It could not be used with a real 24-volt battery, which is an integral unit that can't be switched around the same way as separate batteries in a bank system. And nol, it wouldn't work well for "but can't I charge the two 12v batteries and then use them to charge the 24v battery?" because 24v is enough to runa 24v motor, but not charge a 24v battery.

As for rewiring alternators and changing output parameters...there's experimenting, and then there's d***ing around. Alternators are wired up for specific voltages and loads for reasons, as are the regulators used in them. Can you repurpose them? Sure. Improve on what the engineers have already designed them for? Not likely. You can have lots of fun learning about sparky things, but that's the difference between abstract d***ing around for fun, versus getting a job done.

[Seahunter]

Unlike a generator an alternator doesn't know it's 12, 24, 16, 18 or 48 volt. As a kid we used to mess around with old GM alternators combined with an old lawnmowers to create our own 110v APUs, even 200v + welders with big case GM alternators by stripping out and rewiring the diode block. (Do a Google search) You can buy any number of commercially produced rectifier packages today to convert your cars alternator to produce 110 volts (AC or DC). It's all about the wiring of the feedback voltage to the diodes. The alternator's output voltage is determined by the regulator circuit which reads the electrical system voltage and allows charging as the system voltage drops below the regulator's designed in voltage setting. If the regulator fails in an open setting it can fry your electrical system with 80+ volts. You could duplicate the same circuit destruction by disconnecting the battery when the engine is running and bypassing the alternator's regulator circuit then connecting 12 volts directly to the alternator's field circuit with the engine running; you will see the system voltage soar way above 12 volts. In effect this is what regulator voltage combiners do, but in a controlled manner. They control the output of the regulated voltage shifting between the 12v battery bank voltage system whether 24V, 36V or 48V. The better question would be; "will the diodes on my alternator handle the voltage?".

[senormechanico]

Seahunter's post +1

[FlyingCloud1937]

Originally Posted by Seahunter

Unlike a generator an alternator doesn't know it's 12, 24, 16, 18 or 48 volt. As a kid we used to mess around with old GM alternators combined with an old lawnmowers to create our own 110v APUs, even 200v + welders with big case GM alternators by stripping out and rewiring the diode block. (Do a Google search) You can buy any number of commercially produced rectifier packages today to convert your cars alternator to produce 110 volts (AC or DC). It's all about the wiring of the feedback voltage to the diodes. The alternator's output voltage is determined by the regulator circuit which reads the electrical system voltage and allows charging as the system voltage drops below the regulator's designed in voltage setting. If the regulator fails in an open setting it can fry your electrical system with 80+ volts. You could duplicate the same circuit destruction by disconnecting the battery when the engine is running and bypassing the alternator's regulator circuit then connecting 12 volts directly to the alternator's field circuit with the engine running; you will see the system voltage soar way above 12 volts. In effect this is what regulator voltage combiners do, but in a controlled manner. They control the output of the regulated voltage shifting between the 12v battery bank voltage system whether 24V, 36V or 48V. The better question would be; "will the diodes on my alternator handle the voltage?".

Really check it out

Originally Posted by FlyingCloud1937

If you're really interested in doing this follow this link and read all about it

http://www.microcogen.info/index.php?PHPSESSID=t27gpdebsrbkvb9fm7je738a95&top ic=157.msg1359#msg1359

I know the fellow that wrote this white paper, and the system has been thoughtfully tested and confirmed.

Lloyd

I don't have a dog in this hunt, but if you want know.


(pdf) high output/efficiency alternator white paper

Lloyd

[James S]

Welcome to the forum Sam

[sjemery]

Hi guys,
I am in the beginning stages of restoring a 42' Bristol trawler and I want to purchase a 24v windlass and bow thruster but I want the rest of the boat to be 12v. Can it be done? I am also looking for help in designing the ac and dc electrical systems for $$$ to the right person.
Steve

[Andina Marie]

The 24 volt batteries should be located as close to the windlass and bow thruster as possible.

If your windlass and bow thruster don't draw more than 80 amps you can use a Trollbridge24 to charge from a 12 volt line coming from the starting battery (or house battery). If they draw more than that you will have to look into a 120 volt supply running a dual output charger.

[sjemery]

The windlass I am looking at is a Lofrans and it draws 70 amps at peak load. If I use it in concert with the thruster, which I envision a possibility during windy anchoring, then the draw will be over 80 amps. I have a single Cummins diesel 12vdc and a Northern Lights 8Kw genset also 12vdc being installed. The thruster and windlass of course will be up forward, and two 12v batteries in series will be forward as well....about 3' from the thruster and windlass so no problem with voltage drop there. I want the main engine alternator as well as the genset alternator to charge the starting 12v batts and the house batts AND to replenish the 2 batts in series 24v. Am I asking too much or is this do-able?
Thanks again,
Steve