Questions about wire size to battery banks.

softdownsoftdown Solar Expert Posts: 3,509 ✭✭✭✭
Been a million threads along these lines. But none with this (my) scenario. Solar panels will generate about 3.4 Kw but I am going to only use half for awhile due to uncertainty about a Gel battery bank that I wound up with. Gel battery recommended charging rates seem to literally be all over the place.

One 48V bank of ED8s.....4 feet from controller and inverter
One 48V bank of 109Ah Gels (Alpha Cells-Alpha owns Outback)....5 feet from controller and inverter

Three days from now a local solar tech will try to make the system operational. So I have to have my "ducks in order" so to speak.

Been planning to use 4/0 aluminum wire because I own several hundred feet of it. But I don't have battery cable connectors for it and it is somewhat doubtful that the local town will carry them, It is also very, very stiff.

I also have plenty of #4 AWG copper wire and battery cable connectors and a crimping tool. I used almost all of my #2 AWG making battery cables.

My brain is currently fried. The sewer line filled with tree roots. I "rota-rootered" until midnight. Plus I have misplaced my best solar book.

My instincts tell me 0/0 or 2/0 copper wire might be appropriate in the long run. But I can make the cables out of #4 AWG in 1/2 hour since I already have the needed stuff here. Seems it might be fine for a bit.

Thanks in advance. Admonishments are not needed at this point in time.
First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries


  • PhotowhitPhotowhit Solar Expert Posts: 5,656 ✭✭✭✭✭
    Well first things first how are you hooking them up? Will you use a common line from the battery to a breaker for your inverter, then hook up your charge controller to that? There is no reason to have 2 sets of wire to a battery bank. How are you separating your 2 battery banks? typically you will want to charge and use them separately as different batteries, particularly batteries of 2 different chemistries, don't tend to play well together.

    Are we talking single strings of each battery? so a 48 volt 109 Ah bank and what ever Ah rating the ED8's are? Also what will be the current input to and output from the battery banks?

    My guess is if you have a single string of 109ah batteries, 4 gauge would be fine, I don't think you will be sending more than 15 amps to the bank or drawing more than 15 amps off the bank....
    ...but it's all about the current so we need to know the size of the banks and the current flow into and out of, you can size your fuse or breakers to protect the wires
    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, 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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