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whats the best way to wire 40 SLA batterys in parallel

Discussion in 'Power Electronics' started by Jake Hoffman, Nov 27, 2016.

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  1. Jake Hoffman

    Jake Hoffman

    Nov 27, 2016
    Greetings everybody! :)

    I have 40 SLA 7.5 amp hour 12 volt batterys. I want to wire them all in parallel to make a 300 amp hour battery pack to use for emergency power in my home for power outages that happen about 3-4 times a year. I already have a 12 volt 600 watt pure sine wave inverter. My primary want is to be able to run my big screen TV and the computer thats plugged into it...that whole load averages about 300 watts. The bank is going to spend most of it's life sitting on the trickle charger.

    I could just simply wire them all in parallel with fuses, but I'm afraid one or more of them is going to die eventually and drop to 6 volts or something and tax the others. My thought was 40 small diodes sent to a common bar and then to the trickle charger and then 40 more diodes to another common bar going to the inverter. This way, if one drops its voltage, it won't wreck the others, but instead it just won't have enough voltage/pressure to contribute to the discharge bar. If is sized them just right, could they double as fuses as well? An actual proper BMS is not really an option because the budget is limited.

    I also have 10 trickle chargers lying around so I could also break them into banks of 4 on the charging front but still use diodes or maybe switches to put them onto the discharge bar. Conversely , if charging them all as one bank, I have a 13.8, 14 amp radio shack power supply since they won't have to be recharged very quickly.

    I'm open to any better ideas. I know it all sounds odd, but the batterys were given to me for basically free and I'm just trying to utilize what I have.

    Thanks for reading.

  2. Bluejets


    Oct 5, 2014
    Not a good idea. A fault in one leads to the rest dumping massive current into the fault.
    Not to mention charging difficulties.
  3. duke37


    Jan 9, 2011
    I have a capacitor box out of a transmitter. A couple of dozen electrolytic capcitors were connected with individual wires to the output terminal. One of the wires had melted presumably due to a faulty capacitor.
    I suggest that you connect each battery to a common bus with a fusible wire which will take account of a faulty battery. You will not need diodes and one battery charger will do.
  4. Jake Hoffman

    Jake Hoffman

    Nov 27, 2016
    so i'm sure that will protect me if one reverses polarity or something like that, but tell me what do you think would happen if one drops to 8 volts or something like that? would that not blow the fuse, but still drain from the others terribly? that's why i'm talking about a weak battery cannot drain the other batterys on the bus bar. is there another way to attend to this potential problem besides an expensive BMS system....a "getto" BMS system maybe?

    am i overthinking this or what?

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