diy solar

diy solar

mixed AHr batteries in a LiFePO4 environment (in a mobile application)

1holaguy

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Oct 24, 2020
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I recently replaced my old wet cell battery bank with a new 200 Ahr 12v SOK bank (2- 100 AHr batteries). Recently will published a Youtube on a cheap DIY-build he made using 280 AHr cells for around $200. I believe they were B grade and likely only about 80% of stated capacity, but I was thinking if I can add another 200-240 ahrs for that kind of money (plus a BMS) it would be worth while. Question though is are there problems with this kind of addition as long as the voltage (12v) and battery chemistry remains the same?
 
Building from cells of a "random" quality presents additional complications than cells that are more consistent. You may have cells within the same battery that are poorly matched to each other, and may not perform well as a single battery, let alone in parallel with another.

When paralleling batteries of different capacities, it's important to confirm that they are operating within specifications. Easiest way is to use a clamp ammeter and measure current going through each battery. Hopefully, they are sharing the load proportionally to their capacity, and they are operating within specification.
 
So, I have already purchased 2- 12v-100 Ahr SOK batteries to replace 4 - old 6v wet cell ones. The two new batteries at 80% usage will yeild more AHr than the old four. That will likely work for us based on our current style of usage. If not I will need to consider to either buy additional 100 AHr batteries or do a DIY-build. For what another 100 AHr SOK will cost I can build a 280 AHr DIY. Even if the output of the DIY is 25% less than claimed it would still be almost twice what comes from the 3rd 100 A battery. Adding a 3rd 100A unit a year from now will likely not match the two I just bought anyway. Are the differences that great?
 
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