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Correcting 8*200Ah Parallel Battery Bank


Kilowatt Power

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Greetings,

I visited a site where 8*12V*200Ah batteries were wired in parallel a year ago and now discharge pretty fast on 500W load. A simple battery capacity/voltage monitor showed the SOC move from 100% to 70% in 10 minutes.

The charging system is composed of 1800Wp solar panels, Outback FLEXmax 60 MPPT charge controller and 8 x Gaston GT12-200AG polygel batteries in a straight, long parallel connection.

Other than attempting perfectly balanced charging on the bank as per attached image, what other improvement can be done to revive the system? 

 Balanced Charging.png

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To charge those batteries from 0 to 100% will take about 20kWh of energy. The 1800W of panels will produce about 9kWh per day with no load. I would say that the batteries are not fully charged, and with no load it will take 2 days of charging  to fully charge them to float. If one of the batteries has become damaged by the prolonged state of undercharg that can exacerbate the problem. Fortunately with that battery configuration you could just remove the damaged battery.

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22 hours ago, Kilowatt Power said:

Other than attempting perfectly balanced charging on the bank as per attached image, what other improvement can be done to revive the system?

Your diagram shows a better but not perfectly balanced arrangement; modules B, C, F, and G will contribute less than the others since they have paths that carry higher current (I think; these things always confuse me). You could consider yet one more layer of "diagonal takeoff" to make it "perfect" sharing.

But the modules will be at very different states of health now, so perhaps you don't want perfect sharing anyway. I'd first charge and test each module individually to see which if any have any life left in them.

If they are flooded, check the water and specific gravity. Perhaps try a desulphator, but I'm rather sceptical of those things. I'm afraid I don't hold much help for them, though perhaps some that were far from the cables might not have had much hard work and might be usable.

12 V is such a low system voltage, even for small inverters; it's just asking for problems with cables and current sharing.

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