12v from 48v Array?

Hi all,

I have a 48v battery array, consisting of 8 x 6v batteries. This runs my inverter.
However, I need to power some 12v loads too. I have easily figured out how to tap 12v off of two batteries at any number of points in the array, and am running my 12v loads from this currently.
The problem of course is that the two batteries supplying 12v become out of balance with the rest of the 48v array - they become run down. Just little loads like phone chargers would be ok, but I run lighting and a water pump at 12v. Occasional equalization isn't enough to keep these two batteries in balance with the array... I think I would have to equalize much too frequently to keep things balanced.
I have tried to figure out if there is a way to wire the batteries so that I get 12v from all the batteries, which would be four pairs of 12v parallel. I couldn't figure it out on paper, but chalked that up to not enough brain cells ;) So I got in there and played with the volt meter, but I can't seem to figure it out.
Does anybody out there know just a little more than I do?
I would like to run about 100 watts at 12v. Of course I can't afford to buy a 48 to 12 converter (if I could, I wouldn't be posting all this).
Also I know that there is a balancer made by Solar Converters, Inc. but this thing isn't really fused and I have blown through two of them just with tiny momentary shorts while wiring/troubleshooting.
Thank you,


  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: 12v from 48v Array?

    I think your only choice is a DC-Dc converter.

    I just bought a ~$13 off ebay - here's the description:
    DC/DC Converter PT4841A 48V In to 15V/3.3V/1.5V Out 65W

    The 15V @ 4A can trickle charge a 12V battery that powers your surge loads.
    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: 12v from 48v Array?

    It is (as I'm sure you know) a very bad idea to tap off a larger bank to get a smaller voltage. No matter how little the load, or how large the bank, there will inevitably be system imbalances as you have found our. Changing out the lighting to run on 120vac shouldn't be to hard to do, assuming you invert for 120vac loads anyway. The 12 volt pump is a bit of a problem however.

    A voltage controller for the pump would be he best way that I know to deal with this. Is the pump truly a 12vdc pump, or can it run on 24+ volts? I know that some of the surflos are designed to run 12 or 24vdc. They just pump faster at 24. In fact, I have a voltage doubler to run my surflo on 24 from a 12vdc bank.
    http://www.powerstream.com/dc12-48.htm Under $100 for 100 watts, sure sounds cheaper than killing a battery, or spending fuel and time eqing a battery bank.

  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    Re: 12v from 48v Array?

    ICARUS is correct . NEVER EVER tap off a 48v or for that matter any other high voltage battery source to get 12v you just going to kill the battery you tapped off, even if it very small load. get DC TO DC converter. DIY electric car builder suppliers have ones that are good.