Need to clarify a battery connection set up

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Islander
Islander Registered Users Posts: 6 ✭
in Solar Beginners Corner #1
Hello again. Three or so months back I got four six volt batteries to use on a 24 volt inverter. Now i'm getting an additional 4 in hopes of setting it up in series-parallel. I've seen a vid doing this with four six volt batteries and read up on it, but i just want to make sure I have the right idea before i end up screwing something over. So here is my (poorly) drawn picture of how, to my understanding the batteries need to be set up in order to get 24 volts in series parallel.

Attachment not found.




Please excuse the horrid drawing, I'm horrible at using the paint program. One other question, If in the event i were to add more batteries to this existing setup for the sake of adding more amp hours, I would only need to to connect the positives and negatives to the terminals on the far-side of the batteries and not connect any more on the terminals located in the center of the bank correct?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #2
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    Re: Need to clarify a battery connection set up

    Your drawing would be for two 12 volt batteries in series, then the rest in parallel.

    For a 6 volt battery, you need to put 4 in series, then parallel for a 24 volt bank.

    Note that your drawing is a "Laddered" bank. Problem is the batteries at the "bottom" are closer to the point of use, and see lower resistance to loads/charging and will get deeper cycling. The batteries at the top of the drawing are farther away and will see less current. So, the bank will age/cycle unevenly.

    Batteries have very low internal resistance and the wiring will "steer" the current in the battery bank.

    To fix, take the right wire and run it from the "top" right terminal in the bank. And now all batteries see the same wiring resistance.

    Here is a good link to read:

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

    Personally, I am not a big fan of paralleling batteries together. if you can get larger AH rated batteries (or even 6/4/2 volt cells), that will reduce your number of paralleled strings.

    I would suggest that one series string is ideal. Some folks like two parallel strings--If one string fails, the second they can still limp with until the bad string is fixed/replaced. And I would suggest that 3 parallel strings would be the maximum unless you have no other choice and need more parallel strings.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Islander
    Islander Registered Users Posts: 6 ✭
    #3
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    Re: Need to clarify a battery connection set up
    BB. wrote: »
    Your drawing would be for two 12 volt batteries in series, then the rest in parallel.

    For a 6 volt battery, you need to put 4 in series, then parallel for a 24 volt bank.

    Note that your drawing is a "Laddered" bank. Problem is the batteries at the "bottom" are closer to the point of use, and see lower resistance to loads/charging and will get deeper cycling. The batteries at the top of the drawing are farther away and will see less current. So, the bank will age/cycle unevenly.

    Batteries have very low internal resistance and the wiring will "steer" the current in the battery bank.

    To fix, take the right wire and run it from the "top" right terminal in the bank. And now all batteries see the same wiring resistance.

    Here is a good link to read:

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

    Personally, I am not a big fan of paralleling batteries together. if you can get larger AH rated batteries (or even 6/4/2 volt cells), that will reduce your number of paralleled strings.

    I would suggest that one series string is ideal. Some folks like two parallel strings--If one string fails, the second they can still limp with until the bad string is fixed/replaced. And I would suggest that 3 parallel strings would be the maximum unless you have no other choice and need more parallel strings.

    -Bill


    Thank you very much. When ever these batteries are done i'll be getting better ones. I was a bit pressed for time and cash at the time when i ordered the first set of batteries and i heard that it's not a good idea to mix batteries of different apmhour and voltage ratings so i was pretty much stuck with batteries that were not ideal but could get the job done. Thanks again for clearing things up for me.
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