Wiring 42 12 volt 35 AHr Batteries in a 12 volt configuration
hermit Solar Expert Posts: 25 ✭
These batteries were gifted, what to do with them? Make my shed a source of power. I have a 3000w 12v inverter with 2 sets of inputs (2+ AND 2-) I have bus barred 3 sets of 14 parallel batteries. Question which is the best way to hook up these 3 sets of batteries to each other for both charging and for the inverter. The reason why there are 14 X 3 is that what fits on the shelf. I used aluminum bus bar. The inverter needs to be hooked up with 2 positives and 2 negatives. Do I tie all strings at both ends together both on the positive and negative sides, or do I tie 1 end of string to the opposite side of string then again to the opposite side of the string to the other string (kind of like series but not positive to negative) or tie the 3 strings together with just 1 positive on 1 side and 1 negative on the other side. The answer will determine which way I hook up my charging. Then which would be the best way to wire up the inverter which needs 2 positives and 2 negatives? I know this parallel configuration is bad for charging and troubleshooting but this is what I have. Thanks for you input.
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First of all, my advice is to forget this configuration. The operational problems of 42 lead acid batteries in parallel are just too great to contemplate.
If you insist on doing it anyway, read the information at smartgauge.co.uk, The page How to correctly interconnect multiple batteries to form one larger bank will give you some idea of the problems involved.
The "ideal" four battery solution shown there can be extended to 8, 16, or 32 batteries without much trouble (but a spaghetti pile of long wires and a maintenance nightmare?!), for 42 you will have to compromise some.
Is there any way that you can use a 48 volt system instead? That would reduce the complexity of the battery wiring but you could only use 10 strings of four batteries each and keep the other two as spares. I would not really recommend that either, but it would be better than 42 in parallel!
And before you start, do you know enough about the history of the batteries to be confident that they are good? If they sat for months without being charged they could have lost much of their capacity.
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Even wired for 48 volts, you're over 3 times what can be expected to work. Try to sell them now as used but working batteries - - - or keep them and prepare to sell them for scrap.
At least fuse groups of three or four batteries maximum.