Hi, i have a lifepo4 24v 50ah pack that is losings about 3ah per week while resting, it doesn't seem to stop. I tested loss after 1,2,3 and 4 weeks of resting. resting for a full month it lost about 12ah. My cell difference seems stable at about .010v. doesn't seem like one cell is dragging the pack down but I'm pretty new to batteries so not sure. the pack is about 3 years old. What are some issues that could be happing here? thanks!
Pack discharging
- Thread starter KnewB
- Start date
sunshine_eggo
Happy Breffast!
At resting voltages, cell differences are rarely more than your stated .01V. dV only matters outside 3.10-3.40.
How did you test to determine you lost capacity?
A 12ah loss over 30 days would be a continuous 0.016A draw. If the BMS is continuously active and monitored, I could see this happening. I'm using a JBD connected via UART to USB to a Raspberry Pi running Venus OS:
It's lost about 20% in 11 days:
Worth noting that I haven't used this battery for anything at all. The SoC is not consistent with the resting voltage either.
Basically, the BMS being actively monitored via interface with the Raspberry Pi is draining it.
How did you test to determine you lost capacity?
A 12ah loss over 30 days would be a continuous 0.016A draw. If the BMS is continuously active and monitored, I could see this happening. I'm using a JBD connected via UART to USB to a Raspberry Pi running Venus OS:
It's lost about 20% in 11 days:
Worth noting that I haven't used this battery for anything at all. The SoC is not consistent with the resting voltage either.
Basically, the BMS being actively monitored via interface with the Raspberry Pi is draining it.
I just put it on a hobby charger and measured how many ah went back in after a period of time.
I was kinda wondering if it was the BMS because i just changed the bms to a Jk BMS with a active balance built in. I only balance over 3.40v. The power light on the bms is always on but it just a little led. how can i check to see if its the bms thats causing this?
fyi i felt like i was having some capacity issues before i switched the bms, it was actually the reason i switched to a smart bms.
sunshine_eggo
Happy Breffast!
Valid. I use that method too.
Fully charge and disconnect BMS completely for a week. Reconnect and repeat your charge test. Compare to prior 7 day results.
wouldn't the bms show that its under load if something is draining the battery?
sunshine_eggo
Happy Breffast!
Not if there's nothing passing across the BMS shunt circuitry.
I would not expect BMS self-consumption and any losses due to balancing to be counted.
Steve_S
Offgrid Cabineer, N.E. Ontario, Canada
Active Balancing does not use actual power, it simply moves it power from Hi cells to Lo cells when the conditions are met, otherwise it does nothing and consumes no power. The BMS itself does use a small amount of power but nothing significant. If it has HEAT Function that can hit the battery.
The BMS will not register "internal power use" (its minimal) and with a terribly light load of <0.2A it will register it but not great.
Do as SunhineEggo suggested for a test... That's the 1st step to troubleshoot.
Hi, I did the test and the battery only lost .43ah, was losing 3ah. So I guess it’s the BMS draining it, what could it be? Why would the bms be draining that much? Thanks
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