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Thread: 12v or 24v ?

  1. #1

    Default 12v or 24v ?

    Need some advice! We currently use a 12v system in our off grid home, and have a bit of 12v gadgetry along the way (water pump, TV, lights, etc). In seeking to upgrade I accidentally purchased a very nice 24v inverter. So the question is, should I purchase a 24v charge controller, rewire battery bank for 24v inverter and just use a converter for the 12v stuff; OR should I leave it 12v and purchase a different inverter? I know that 24v is supposed to be more efficient, but not sure if the converter would offset the benefits. Perhaps I am putting too much thought into a mistaken purchase? Thanks for any help!

  2. #2
    Join Date
    May 2009
    off grid retirement in Northern Calif


    it all depends, you likely have ironed out all your bugs in the existing 12v wire runs, and making the change to 24V will render all 12V appliances useless.
    Don't even think of taking a 12V tap off a 24V battery, the batteries will become imbalanced, and fail rapidly.

    So what was the reason for the desire to upgrade? More appliances needing more 120VAC and the old inverter did not supply enough?

    Rule of thumb, the first 1Kw of AC, you can do with 12V, beyond 1KW, you need to sep up to 24V, because the current requirements over 1,000 watts at 12V, exceed 100A, and the losses in the wires and connections, become excessive, and you start getting brownouts in the inverter, where it cant get enough input power.

    Maybe keep a couple batteries in the 12V circuit, move others to the 24V system and use a small efficient 120V charger to keep the 12V bank topped off. I'm guessing you have 6 or 8 batteries in your bank currently ?

    (back from 2 weeks in the sticks and no internet, and lots of catching up to do.)
    Since the dawn of time it has been mankind's dream to blot out the sun.
    Montgomery Burns

    "Always listen to experts. They'll tell you what can't be done and why. Then do it."

    spreadsheet based voltage drop calculator:


    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,
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    Setting up batteries http://tinyurl.com/LMR-NiFe

    gear :
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||

    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||

    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

  3. #3


    Thanks for the great reply! It was late for me last night, brain was fried, and I probably didn't give enough information. We have a very small setup : one 80 watt panel (will be getting another), and (4) 4D batteries - about 800 amp hour. We use so little 120v currently that we are just using a cheapy 200 watt inverter. I was wanting a pure sine inverter to run a front loader, so I purchased a Xantrex Prosine, but 24v accidently. Thought about reselling it, but not even sure where I could do that except Ebay. Anyway, I knew not to "tap" a battery, but was wondering about a DC to DC converter to drop the voltage back down to 12v from a 24v system. I am wondering that even with planned expansions our system will still be small enough that any savings in efficiency may be negligible?

  4. #4
    Join Date
    May 2009
    off grid retirement in Northern Calif


    It depends on the front loader, it will be happier running from a 24V inverter (inverter and batteries will be happier anyway) . Or ebay it.

    You can use a MPPT controller (it works like a DC-DC transformer) to down convert 24V, to 12V battery charging, but you still need the 12V battery too.

    Expanding up to 24V, if you even faintly think your loads will increase, do it now, instead of 2 years from now. You will need a 24V charge controller, I'd suggest moving to MPPT, instead of PWM, and you will certainly need more solar PV to run the washer.

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