Need 24 volts from 12 volt battery bank

System
System Posts: 2,511 admin
in Off Grid Solar & Battery Systems #1
A friend recently gave me a beautiful SolarOne battery (1600 amp hours at 12 volts) and I am wanting to work it into my new system. The only problem is I really wanted to go with 24 volt system voltage to accommodate my 1800 watts of solar without having to buy so many charge controllers. Also I would like the increased flexibility with larger loads that 24 volts would yield. I do currently have a 12 volt 2400 watt Xantrex TR series inverter but was planning on stepping up to a larger Outback or Magnum sine wave model.

Since I really would like to go with 24 volts and have not purchased my new inverter yet, I have a simple question...is there a very large DC transformer available that can step up my 12 volt battery to 24 volts with sufficient amperage to support a 3500 watt inverter plus a couple small DC loads? If not, what are your suggestions, considering that the 12 volt battery (a $4,500 value) is here to stay and I just need to make the best of it.

Thanks for your help!
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Need 24 volts from 12 volt battery bank

    Sorry; nothing but bad news. :blush:

    For one thing there's no such thing as a "DC transformer". You simply can't step DC up or cut it down the easy way like you can with AC. You need a DC to DC converter, and those are not designed to handle the high current loads of inverters.

    For another, that 12 Volt battery would still have to be charged as a 12 Volt battery. You're looking at (rough calculations, not an exact recommendation):
    160 Amps (10% rate) @ 14.4 Volts charging = 2304 Watts less typical 77% efficiency derating = 3kW array.
    With at least two charge controllers to handle all that power.

    I think you right in wanting a 24 Volt system. I don't know about that specific battery, but some of the industrial/forklift units can be reconfigured for different Voltages.

    Sometimes a bargain isn't a bargain, even if it's free.

    Maybe someone else has a better idea.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #3
    Re: Need 24 volts from 12 volt battery bank

    I'd say use what you got, use the battery, use a single C60 charge controller and What ever you envisioned using in a 24V configuration,(likely something that will handle every thing in a 24 volt configuration) charge controller. and spend the money you saved on a battery and inverter and buy more panels.

    Keep in mind when the battery fails you will switch to a 24 volt system, so buy panels that will work in such a configuration well.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #4
    Re: Need 24 volts from 12 volt battery bank

    I recently saw a 12 volt to 24 volt DC-DC converter that will handle 540 watts, so there is one option.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #5
    Re: Need 24 volts from 12 volt battery bank
    techntrek wrote: »
    I recently saw a 12 volt to 24 volt DC-DC converter that will handle 540 watts, so there is one option.

    Due to surges etc, unlikely it could supply much more than a 2 or 3 hundred watt inverter. Be far better to go with 12 volts and be done with it. OR, sell the battery and put the money on a 24 volt system.
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  • bmet
    bmet Solar Expert Posts: 630 ✭✭
    #6
    Re: Need 24 volts from 12 volt battery bank

    If the SolarOne is available as a custom order in every configuration, can it be re-wired for 24V?
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #7
    Re: Need 24 volts from 12 volt battery bank
    techntrek wrote: »
    I recently saw a 12 volt to 24 volt DC-DC converter that will handle 540 watts, so there is one option.
    Maybe not. That might work for the output, but it won't work backwards to charge the battery from a 24V charger. He would also discharge the battery more than twice as fast, since volts are swapped for amps (540W = 22.5A @24V = 45A @12V), and no system is lossless, so it's worse than that.

    My advice would be to go out and buy an identical 12V battery and put them in series.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #8
    Re: Need 24 volts from 12 volt battery bank
    ggunn wrote: »

    My advice would be to go out and buy an identical 12V battery and put them in series.

    Agree, but bear in mind that the resulting battery pack is going to need a relatively large PV array to properly charge and maintain it. Also, what is the age of the original battery? More than a few months difference, or if one is reduced in capacity, it could take the new one down with it. Complicated stuff unfortunately. Nothing is simple :cry:
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #9
    Re: Need 24 volts from 12 volt battery bank
    waynefromnscanada wrote: »
    Agree, but bear in mind that the resulting battery pack is going to need a relatively large PV array to properly charge and maintain it. Also, what is the age of the original battery? More than a few months difference, or if one is reduced in capacity, it could take the new one down with it. Complicated stuff unfortunately. Nothing is simple :cry:

    Ah. Somehow I had gotten the impression that it was a new battery, but reading back, I see that the OP just called it "beautiful".
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