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

[Fuss]

I was wondering if this would work.....
They say that if you disconnect an alternator from the battery then then voltage increases until it blows the diodes at some high rate probably over 60 volts.
So...
I thought the following should be possible... Take a 12v alternator and connect the battery sense wire to the 24v battery using the middle terminal so only 12v is seen by the regulator. Connect the positive terminal at the 24v battery terminal.
When run the alternator will only see 12v and output a higher voltage as it puts its full amperage in until the voltage seen rises to 14.4 or whatever the regulator is set to.

What do the experts think????

Thanks John

[Florida Mike]

The short answer is no. The explanation why would take more room than is available here. My two cents, Mike.

[Fuss]

Originally Posted by Florida Mike

The short answer is no. The explanation why would take more room than is available here. My two cents, Mike.

Hi Mike,
thanks for the comment... do you know what happens when you put a 24v regulator on a 12v alternator and connect it to a 24v battery?

[goboatingnow]

The solution is a boost convertor and integrated charger. Technically straightforward. Grease my palm with $$$ and I'll design you one.

Otherwise just forget it.

Dave

[Rick]

You CAN use a 12V alternator with a 24V regulator to charge at 24V with no gimmicks. You will have to derate the power that the alternator will deliver at 24V from its 12V power rating yet it will work.

[witzgall]

Interesting Rick. Could this also be done to use a 12v alternator to charge a 48v battery bank?

Chris

[Lancerbye]

An alternator is actually a 3 phase ac generating unit which is capable of producing over 120 vac before rectification. once rectified and producing over 100 vdc at a higher rpm, it has the capacity to drive an electric drill and many other power tools that use universal brush type motors. So yes you can get a high enough voltage to charge a 48 volt bank, however the current capacity is dependent on the internal capacity of the alternator and the voltage will not get over 48 volts until there is a fair rpm happening. The regulator regulates down, not up.you will need a 48 volt regulator.

[Florida Mike]

As was said by someone further up you need to cut back the output of the alternator. An altar there has a rated output of both volts and amps. If you multiply volts times amps you get watts, basically watched equals heat in the alternator. If you want to raise the output of the alternator you need to figure the watts and keep that about the same or less. The same theory would go with 48 V bank. Keep in mind 12 V alternator is rated at 14 V., so you need to figure 24 V system is actually 28 V and so on. If you are determined to do this one thing that will help is to remove the diode pack and mounted on the heatsink. I only did this once with an internally regulated General Motors alternator and to cut down the output I clipped one of the three phases. This alternator was on a front end loader and only had to recharge the batteries as there were no other loads. I never checked its output other than voltage. Keep in mind heat is what kills most alternators. Again this is just my two cents, Mike.

[Fuss]

Thanks very much for all the feedback.

After reading all the posts it seems that it will work. The sense wire to the middle post of the battery so that the 12v regulator sees 12v and the battery + to the 24v post. The only problem then is over heating the alternator ....this could be solved by putting a reostat or some other voltage limiting device on the field wire so that the current output by the alternator is limited.

I think these ideas are good for the general cruising community to know as it could help out substantially in an emergency.

I will try it when I have some time and report back. I have a spare 12v alternator and that was the reason for the question...

(everything onboard should be good for 2 jobs)

Thanks again
John

[Maine Sail]

Originally Posted by Fuss

Thanks very much for all the feedback.

After reading all the posts it seems that it will work. The sense wire to the middle post of the battery so that the 12v regulator sees 12v and the battery + to the 24v post. The only problem then is over heating the alternator ....this could be solved by putting a reostat or some other voltage limiting device on the field wire so that the current output by the alternator is limited.

I think these ideas are good for the general cruising community to know as it could help out substantially in an emergency.

I will try it when I have some time and report back. I have a spare 12v alternator and that was the reason for the question...

(everything onboard should be good for 2 jobs)

Thanks again
John

What are you trying to accomplish that your alternator is not doing? Are you trying to charge a 24V bank or 12V bank? More info would be great..

[goboatingnow]

Originally Posted by Fuss

Thanks very much for all the feedback.

After reading all the posts it seems that it will work. The sense wire to the middle post of the battery so that the 12v regulator sees 12v and the battery + to the 24v post. The only problem then is over heating the alternator ....this could be solved by putting a reostat or some other voltage limiting device on the field wire so that the current output by the alternator is limited.

I think these ideas are good for the general cruising community to know as it could help out substantially in an emergency.

I will try it when I have some time and report back. I have a spare 12v alternator and that was the reason for the question...

(everything onboard should be good for 2 jobs)

Thanks again
John

That simply will not work. If you want to charge 24 v from a nominal 12 v system then you need to change the regulator.

Dave

[fairbank56]

Originally Posted by Florida Mike

If you multiply volts times amps you get watts, basically watched equals heat in the alternator.

An alternator generates power, it doesn't consume it. Heat in an alternator is due primarily to I²R loss but also includes hysteresis loss, eddy current loss and mechanical friction loss.

Eric

[hellosailor]

Fuss, before you blow up a batch of stuff, really, start with a cheap book on 12v electrical systems.

Besides trashing the gear, you can also get badly injured with 12v systems. Badly. 12volt, 24volt, same same.

[sam123]

Just registered this nice forum. Hope you don´t get this as spam.

This will do the job:

Battery to Battery Charger 12v to 24v 25Amp - BB122450

Link: Sterling Battery to Battery Digital Chargers

Other choise is to add extra 24V generator to main engine.

BR, Sam

[GordMay]

Greetings and welcome aboard the CF, Sam.