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Nonlinear

Rotating Lead Acid Batteries

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Hi All, I was hoping someone would have some advice on the best way to rotate lead acid batteries. I have a lead acid battery bank consisting of 8 x 12VDC (nominal) connected in a 2x4 bank. They have been in service for more than a year now and after measuring individual cells recently I noticed they are not as even as they should be. I am thinking of taking the first and last cells in a bank and making them third and second respectively and making the original third cell the first and the original second cell the last. Any opinions? Am I over-thinking this?

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What you are suggesting is a good idea. Effectively the inner most batteries become the outermost batteries, so they all get to work harder for a time. This should extend the life of your battery bank, but not by much. 

Most charge controllers will give a periodic equalization charge to try even the battery voltages out. I had the exact problem you had, and it just never went away. It wasn’t that severe a difference (0.3v) so eventually I just forgot about it. One thing I’ve seen done is to fit balance wires between the two bank’s individual batteries. 

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Thanks @Solaris. I do have the balance wires, which I'm hoping helps a little. I wired them as suggested in the BMV manual. I'm using a BMV702 and it has started to alarm on the voltage difference alarm, but luckily not often. Still, I'm a little worried but not too surprised, especially since my Axperts are not known to be very kind to batteries in general. I'm hoping to get a few more months out of them and then probably switching to the PylonTechs. If only there was an inverter that is reputable, well-designed and that can be paralleled to provide the power that my Axperts give.

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Hey Nonlinear

Glad to help. 

Your balance wires will help between the parallel strings, but does nothing for series strings. 

Another thing you can try, although it is a laborious job, is loosen all the batteries and wire them all in parallel. I did this for a customer once and got quite satisfying results. I took all 8 of his 200ah batteries and wired them into a 12v 1600ah battery. You leave them connected like that for 24 hours (don’t connect anything else) and the next day they are almost perfectly in balance. 

Personally I don’t like the “all in one” nature of the Axpert, but almost every customer sees his friends one and wants the same one. I have fitted several of them, but I prefer separate charge controller and inverter myself. 

I use the Devel 6000w inverter and it although small, has served me very well. They are available in 8000w and 12000w, I think there might even be an 18000w .... It doesn’t use fancy electronics to invert 48v to 220v, it uses good old fashioned transformers. They are as heavy as a 200ah lead acid battery, but are very robust. 

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Very, very interesting. Thank you @Solaris. I think I'm going to try that. I will also be googling those Devel systems. Weight is not a significant concern for me but I'm a little space constrained. Do you have any experience with these inverters and Lithium batteries?

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The Devel inverter will work with lithium batteries. There are some Devel inverters in the range that have built in MPPT, but I opted for a plain inverter on its own. I have two Microcare MPPT’s, but if you intend using the pylon tech lithium’s the Microcare  MPPT will have to loaded with custom lithium parameters as the lowest boost charge you can set it to is 54v (too high for pylon tech) and the lowest float charge you can set it to is 53,2v (also too high for pylon tech) When it comes to the Devel with built in MPPT, I don’t have any idea what it’s standard settings are. So do research and choose carefully... 😁

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From what I noticed on my previous battery  bank is that the first battery on the positive side works the hardest, so my plan is to rotate that battery to the negative side and move the rest along one place in the string, once a year.

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i have noted the same  "small" issue with my lithium DIY packs, the BMS does even out the packs at the top end but it does leave a seed of doubt at the back of the mind that something needs to be done. As to whether it is detrimental to the packs only time will tell. I have toyed with the idea of increasing the bass bars on the packs times to reduce resistance there and increasing the size of the packs to essentially slow charge the packs.....

but based on the amount of work that went into building the packs I would rather err of the said of safety and do everything I can to keep the packs safe!

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