Battery wiring

solorone
solorone Solar Expert Posts: 257 ✭✭✭
in Off Grid Solar & Battery Systems #1
What is the current thinking on the best way to wire 8, 12 V. batteries into a 24 V. bank. Currently I have 4 in series and parallel, this give me 2 "home runs" each for positive and negative. Does anyone wire them all together, eliminating the extra home runs, I would think this might cause some problems.
Thanks
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #2
    Re: Battery wiring
    solorone wrote: »
    What is the current thinking on the best way to wire 8, 12 V. batteries into a 24 V. bank. Currently I have 4 in series and parallel, this give me 2 "home runs" each for positive and negative. Does anyone wire them all together, eliminating the extra home runs, I would think this might cause some problems.
    Thanks

    Current thinking is based on facts, and the facts are that when batteries are in parallel it is difficult to get current (amps) to divide equally among the parallel batteries. As a practical matter, two parallel strings is acceptable (but not optimal) and more than that is looking for trouble.

    read: http://forum.solar-electric.com/showthread.php?14674

    If you feel that you must have 4 parallel strings, the best way to do it is to have bus bars with just one home run. The preferred solution is to use a single string of higher capacity batteries.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: Battery wiring

    Smart Gauge shows two ways to do this right (think of each individual battery shown as a string of two for your application). Method #3 or method #4 shown here:

    http://www.smartgauge.co.uk/batt_con.html

    Skip method #2: it does not actually work well with four strings.

    Ideally each string would have its own post terminal fuse too.

    As vtMaps said, many parallel strings can cause problems. Those problems will be worse on 12 Volt and less on 48.
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  • solorone
    solorone Solar Expert Posts: 257 ✭✭✭
    #4
    Re: Battery wiring

    Currently I have 8 12 V. batteries, 4 are wire in S/P with + and - home runs on opposite ends of each 4 member bank. Am I right in reading this is about the best way as posted in the replies. I unfortunately have to rush to hook up the new banks from their new location, as the battery re-cycler is coming Monday to remove my 30 years worth of battery banks. I am hoping to have a very nice payday, at .40 per pound. WOOHOOO.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Battery wiring
    solorone wrote: »
    Currently I have 8 12 V. batteries, 4 are wire in S/P with + and - home runs on opposite ends of each 4 member bank. Am I right in reading this is about the best way as posted in the replies. I unfortunately have to rush to hook up the new banks from their new location, as the battery re-cycler is coming Monday to remove my 30 years worth of battery banks. I am hoping to have a very nice payday, at .40 per pound. WOOHOOO.

    Um, sounds like you've done it backwards; wiring the parallel connections first then the series connections. It should be like this diagram, only each string would have only two batteries in it on account of being 12 Volt units not 6 Volt ones.
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  • solorone
    solorone Solar Expert Posts: 257 ✭✭✭
    #6
    Re: Battery wiring

    I do not see any difference in that diagram, except I am 12 v. and jump + to+ on the next two 12 V batteris, then come off with - on one end of the 4 and + on the otgher end of the 4, same with other 4 battteries in the next bank, I end up with 2 + home runs and 2 - negative home runs, all at opposite ends of their respective banks. I need to swap over tomorrow or Sunday, this battery buuer with the better price, came up all of a sudden.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: Battery wiring

    So you have something like this diagram times two?
    In which case so long as the total length of positive and negative cable for each "set" is equal to the common connection points it should work.
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  • solorone
    solorone Solar Expert Posts: 257 ✭✭✭
    #8
    Re: Battery wiring

    Yes thanks, that was what I was trying to get across, they were wired like that for 13 years, and I guess I will put them back that way. I had some issues with getting cells to level out but that I think was due to my negligence and things beyond my control, such as getting sick 06/09 and not enlarging the system as planned and failing to take decent care with maintenance. using 0000 interconnects and I guess 0000 home run, at 20' this should keep voltage drop down to .22V at 220 A./ 24V. Yes all home runs are = length. We re installing 4KW of new panels, and have a truck load to sell for those that want to play with low output cheap ARCO panels. LOL
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: Battery wiring

    Ideally it would be more like this X2.
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  • solorone
    solorone Solar Expert Posts: 257 ✭✭✭
    #10
    Re: Battery wiring

    Yes that would be better, and I have enough 250/500 MCM brass nuts to make that work, also will make it a bit easier to attach 0000 solid to the bank. I am out of 0000 strand. It might be easier if the + - were not on the same side.
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  • solorone
    solorone Solar Expert Posts: 257 ✭✭✭
    #11
    Re: Battery wiring

    Thanks for the input folks, have surveyed my 13 YO wiring and think I have enough wire, and I can make my connectors from copper pipe, I have 100 feet of #1, not much help unless doubled, must look up the MCM rating for it. Have 100' of 0000 solid/16 strand??. plus the 0000 interconnects came with the batteries, very nice of them, I think I am ready to go with the last diagram. I will do this the best/most efficient way possible, at 69 YO this might very well be my last setup, next time it will fall to my children, LOL, yea lot of luck with that. I guess someone will get interested in the setup sooner or later, have had little luck interesting my kids or Gran's in the system, much less where all the buried plumbing valves are. Oh well such is life. someone will get the farm, and be scratching their head.:cry:
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