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diy solar

Looking for advice on my low voltage cell. Or help in the Atlanta area

Jakeroberts100

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Joined
Aug 24, 2020
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3
Hey lithium lads and lassies

In retrospect I may have made a questionable decision and bought a LiFePo4 battery from a private seller. Everything felt right about it but now revealing several reasons why this was not the wisest decision for someone with my experience level.



now the issue...
I got 4 series 280ah prismatic cells 12 volt battery. Look to be grade A or new. 200amp Daly BMS since I have a 2000watt inverter. When I got them I measured them all at the same voltage (3.6 I think). Put my whole electric setup together for my van (4x100w solar with renogy cc is my only charging setup ) and everything seemed to be running smoothly. Copied most of the components and wiring from Wills 400watt setup. A small issue where voltage would sometimes drop to 5v but I think I solved that was a loose connection in my fan.
Somehow after less than a week I ended up with the cell closest to the BMS reading 2.82v. The others at 3.21v. I was never pulling more than 10amps. The BMS shut the circuit I’m guessing due to the low cell voltage but I thought it had active balancing to prevent this unbalance from happening. Weirdly I still get 1.28 volts from the positive terminal to the BMS output.

does this sound like the cells need to be top balanced. Or could the cell be bad :( ?

one of my reasonings for buying from this seller was I didn’t really want to mess with that/buy the tools to do it. I think I could figure it out, but was also wondering if there is anyone in the Atlanta area who wanted to make some extra cash helping me out? Hope this is allowed here and in the right section.
 
voltage dropping to 5V is not a small issue at all. That's a WTF?! moment, and the cause/corrective action should be fully understood.

Do you have the BMS properly set for balancing?

If you can't test cells, you should always top balance them as that's the only way you'll get peak output.

It's possible that your cells are just poorly matched as there's not a ton of goody left in them at 3.21. Try to use as little power as possible and see what your cells top out at tomorrow.
 
It would go down to 5v randomly while fan was running. I would trip the breaker for the fan and voltage went back to 13v. I would mess with my connections in the fan wiring And issue came back after a few minutes of running normally. After the third time I took my battery out of the system and has been sitting for a couple days now while I tried to research what was happening.

5volt would at least show up on my dinky voltage display I wired into the battery terminals. When I figured out the issue was with the cells the bms had cut my circuit and the voltage monitor showed nothing
 
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I have made no adjustments to the bms Nor do I think I can. I can set some charge parameters in my charge controller Bluetooth app but I don’t believe there is any way to make any adjustments to the bms settings.

are you recommending using my solar panels and charge controller to try to top up my cells. I was thinking this could hurt my cells that are higher voltage but I guess the bms would prevent that. Although now I’m not very confident with my bms
 
3.65V/cell is a typical peak, but they can safely go to 4.2V if necessary. Repeated trips to 4.2 will eventually damage them. For the purposes of testing, 3.8 or 3.9 is no big deal, and the BMS will probably cut them around there.

Fully charge them and see where you are.
 
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