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Old 21-10-2014, 00:17   #1
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Can I still get 12V from two 12V batteries in series

Hi all,

My boat has both 12VDC and 24VDC systems. The engine alternator is 24 volts as well as the main battery banks. I have a Newmar 24V to 12V DC-DC converter output to the 12V bus. I also have a 24VDC to 110VAC inverter.

I have a separate battery bank in the workshop which is two 12 volt batteries wired in series to get 24 volts for my watermaker and a belt driven high capacity bilge pump.

I now want to run some 12V equipment off the same battery bank. I would prefer not to buy a 24V to 12V converter. I was wondering if I could hook up to the pos and neg from one of the batteries that are in series and get 12 volts as well? If so, would I also get the full amps?

Thanks,

Jeff
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Old 21-10-2014, 00:19   #2
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Re: Can I still get 12V from two 12V batteries in series

this drains one battery more then the other. and you can't properly charge them unless you pull them apart with 2 12v chargers. it's just not a good way of doing it.

the 24-12 converter will drain equal power from each battery. then the 24v charger charges them both back up.
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Old 21-10-2014, 09:39   #3
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Re: Can I still get 12V from two 12V batteries in series

I agree with smac999 on this. Could you connect to the 12vdc bus and run the wire where you need it?
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Old 21-10-2014, 10:21   #4
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Re: Can I still get 12V from two 12V batteries in series

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Originally Posted by Mikado View Post
Hi all,

My boat has both 12VDC and 24VDC systems. The engine alternator is 24 volts as well as the main battery banks. I have a Newmar 24V to 12V DC-DC converter output to the 12V bus. I also have a 24VDC to 110VAC inverter.

I have a separate battery bank in the workshop which is two 12 volt batteries wired in series to get 24 volts for my watermaker and a belt driven high capacity bilge pump.

I now want to run some 12V equipment off the same battery bank. I would prefer not to buy a 24V to 12V converter. I was wondering if I could hook up to the pos and neg from one of the batteries that are in series and get 12 volts as well? If so, would I also get the full amps?

Thanks,

Jeff
The answer is "yes you can do that", but since you already have a 24 to 12 volt converter, why would you want to?

Doing what you suggest drains one battery more than the other and is not the best practice.
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Old 21-10-2014, 10:31   #5
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Re: Can I still get 12V from two 12V batteries in series

I was hoping to get away from a long heavy gauge 12V run. I'm thinking of replacing my 24v windlass and found a super deal on a new one but it is 12v. My electrical system is very complicated already so just trying to simplify and not add additional equipment. I did run across a Newmar
24-12-25 which is probably the way to go..........one more piece of electronic equipment to fail
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Old 21-10-2014, 10:39   #6
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Re: Can I still get 12V from two 12V batteries in series

I don't know how much this would complicate or simplify things, but it is not too bad to wire in a switching setup that allows you to switch between 12/24V so you could switch the batteries from serial to parallel whenever you needed to use the windlass.

The only concern that jumps out at me is to verify that the existing wires set up for 24V are big enough to handle the current if it went to 12V.
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Old 21-10-2014, 12:12   #7
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Re: Can I still get 12V from two 12V batteries in series

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Originally Posted by Mikado View Post
I was hoping to get away from a long heavy gauge 12V run. I'm thinking of replacing my 24v windlass and found a super deal on a new one but it is 12v. My electrical system is very complicated already so just trying to simplify and not add additional equipment. I did run across a Newmar
24-12-25 which is probably the way to go..........one more piece of electronic equipment to fail
Drawing a lot of current from one of two batteries in a series configuration is not a good idea. An LED lamp would be OK.

It would be simpler to buy a 24 volt windlass than to buy a 12 volt windlass and a converter. Would that converter handle the current draw of a windlass under load or stalled?
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Old 21-10-2014, 12:57   #8
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Re: Can I still get 12V from two 12V batteries in series

Yes, you are correct that the cleanest solution would be to purchase a 24V windlass but I found a new in box $6k 12v windlass at an estate sale for $500. The converter I just purchased is 25 amp momentary and 20 amp continuous so should be adequate.

Maybe the best solution would be to sell the 12v and purchase a 24v with the proceeds.

Thanks everyone for your options and advice.

Jeff
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Old 21-10-2014, 13:52   #9
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Re: Can I still get 12V from two 12V batteries in series

Maybe the windlass could be reconfigured to operate on 24V? Perhaps a different motor armature is all that is needed to make the change.

Steve
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Old 21-10-2014, 14:08   #10
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Re: Can I still get 12V from two 12V batteries in series

Thanks Steve. Another option I had not thought about.

I read your 12 page thread regarding your re-fit of Panope. I must say that I think your work is phenomenal and gives me encouragement that my remaining projects can and will get done.

She is a beautiful boat and I'm sure you are very proud to keep your families memories alive.

Best of luck,

Jeff
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Old 21-10-2014, 14:18   #11
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Re: Can I still get 12V from two 12V batteries in series

Perhaps consider a 12v battery dedicated to the winch, charged via a regulator connected to 24 volts. Less copper to run. Ensure adequate ventilation. PV regulator would do.
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Old 21-10-2014, 22:49   #12
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Re: Can I still get 12V from two 12V batteries in series

25a converter for a windlass?... more like 100a. they are normally 50-80a

sell the windlass, make profit, buy a 24v one. if you have 24v batteries a 24v windless would be better anyways. smaller wire etc
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Old 22-10-2014, 09:43   #13
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Re: Can I still get 12V from two 12V batteries in series

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Originally Posted by Mikado View Post
I was hoping to get away from a long heavy gauge 12V run. I'm thinking of replacing my 24v windlass and found a super deal on a new one but it is 12v. My electrical system is very complicated already so just trying to simplify and not add additional equipment. I did run across a Newmar
24-12-25 which is probably the way to go..........one more piece of electronic equipment to fail
Several had beat me to the punch with yes but hell on one battery. You might get away with it for the occasional use of a windless.
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Old 22-10-2014, 12:09   #14
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Re: Can I still get 12V from two 12V batteries in series

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Originally Posted by muddyone View Post
Perhaps consider a 12v battery dedicated to the winch, charged via a regulator connected to 24 volts. Less copper to run. Ensure adequate ventilation. PV regulator would do.
This is the option I would go with but I'm no electrician.
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Old 22-10-2014, 13:37   #15
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Re: Can I still get 12V from two 12V batteries in series

Given the bang for the buck, I think I would buy two 12v deep cycle batteries and install them by the winch. And do that with either a switch, or with plain jumpers (high amperage manual DC plugs) so that I could jump or switch the two winch batteries from 12v-parallel to 24v-series mode, at the same time switching them from the winch, to the 24v charging line.

On the downside it would mean manually pulling or setting a couple of switches, and manually connecting "winching mode" versus "charging mode". But if I could save three or four grand by doing it that way?

I don't think I'd mind. As long as I wasn't using that winch coupla times a day, day in and out.
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