24v to 12v Question...

Hi Guys,

Ive been watching this forum for a long time, lots of good info on here. Finally decided to ask a question :D.

Awhile back I read a post about this and the solution I present here was mentioned but I can't seem to find it again and although I'm fairly certain this should work, I wanted to tap the knowledge bank here to make sure.

I'm up against the 12v load from 24v battery bank dilemma and I know 2 of the standard solutions is to:

#1: Get a step down converter.

#2: Have a separate 12v bank.

Well based on my knowledge of electronics(still learning), there is a third solution(I think :D).

Hypothetically, with 2 12v batteries in series(24v), if I were to take a 12v inverter and hook 2 cables of the same length to the + input, one from each battery and the same for - input, would that prevent the problem of the batteries getting out of balance in the system? And what if I was using 6v batteries in a 24v or 48v configuration but instead pulling from sets of 2 for my 12v? I realize on large systems this could become a wiring nightmare but I'm just curious if anyone has tried it and/or what your thoughts are if you don't mind.

Thanks in advance!

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,642 admin
    Re: 24v to 12v Question...
    dannyboy wrote: »
    Hypothetically, with 2 12v batteries in series(24v), if I were to take a 12v inverter and hook 2 cables of the same length to the + input, one from each battery and the same for - input, would that prevent the problem of the batteries getting out of balance in the system? And what if I was using 6v batteries in a 24v or 48v configuration but instead pulling from sets of 2 for my 12v? I realize on large systems this could become a wiring nightmare but I'm just curious if anyone has tried it and/or what your thoughts are if you don't mind.

    Dead short across both batteries (if I understand your wiring example). And can be pretty dangerous with a car sized (or larger) lead acid batteries. They can output hundreds (or even thousand+ amps) into a dead short. And sparks can ignite hydrogen gas in the cells if the battery has been recently charged.

    There are some "neat" ways of getting 12 and 24 volts from a single battery bank. One is to use a DC to DC bidirectional converter. You connect the converter across both batteries and connect the batteries in series for 24 volts.

    You then connect your 12 volt loads to one of the batteries. The 12 to 12 volt isolated converter then keeps each 12 volt battery at the same voltage (balanced) by discharging/charging (transfer of charge) as needed. When the battery bank is being recharged at 12 volts, the converter recharges the other battery too (similar with 24 volt charging).

    As I understand, this is done fairly often on large Motor Homes that have 24 volt vehicle batteries and need 12 volts for some of the loads.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NorthGuyNorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: 24v to 12v Question...
    dannyboy wrote: »
    Hypothetically, with 2 12v batteries in series(24v), if I were to take a 12v inverter and hook 2 cables of the same length to the + input, one from each battery and the same for - input, would that prevent the problem of the batteries getting out of balance in the system?

    If your batteries are connected in series then + of battery A is connected to - of battery B. You will now connect + of the battery A to + of battery B. This will short battery B and it'll melt down. The same with - connection, which will short battery A.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: 24v to 12v Question...
    dannyboy wrote: »
    Hi Guys,

    Ive been watching this forum for a long time, lots of good info on here. Finally decided to ask a question :D.

    Awhile back I read a post about this and the solution I present here was mentioned but I can't seem to find it again and although I'm fairly certain this should work, I wanted to tap the knowledge bank here to make sure.

    I'm up against the 12v load from 24v battery bank dilemma and I know 2 of the standard solutions is to:

    #1: Get a step down converter.

    #2: Have a separate 12v bank.

    Well based on my knowledge of electronics(still learning), there is a third solution(I think :D).

    Hypothetically, with 2 12v batteries in series(24v), if I were to take a 12v inverter and hook 2 cables of the same length to the + input, one from each battery and the same for - input, would that prevent the problem of the batteries getting out of balance in the system? And what if I was using 6v batteries in a 24v or 48v configuration but instead pulling from sets of 2 for my 12v? I realize on large systems this could become a wiring nightmare but I'm just curious if anyone has tried it and/or what your thoughts are if you don't mind.

    Thanks in advance!
    Hope you read the responses before you tried it. :D
  • dannyboydannyboy Registered Users Posts: 3
    Re: 24v to 12v Question...

    @BB & NorthGuy,

    Thanks for the responses, I was wondering about that but was confused by the post I had read(still can't find it). But maybe I misunderstood what was said. I can see very clearly now why it wouldn't work, and as simple as it is I'm surprised it didn't come to me when I was thinking about it. Thanks again!

    @ggunn

    Yes definitely:D, wasn't planning on trying anything till I was absolutely(or at least close to it) certain one way or the other. I prefer to do things that way as much as possible:D.
  • vtmapsvtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: 24v to 12v Question...
    dannyboy wrote:
    Ive been watching this forum for a long time, lots of good info on here. Finally decided to ask a question
    I have one thing to add: Welcome to the forum. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • dannyboydannyboy Registered Users Posts: 3
    Re: 24v to 12v Question...

    Thanks vtMaps!!
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