I have a 48V solar connected to MPPT 100/30, which charges my lithium 200Ah battery (with internal BMS). I have set MPPT to preset battery Lifpo4. On my shunt, I read the max battery voltage to be 15.2V. If I divide that by 4 cells, I have 3.8V per cell, which would be a dangerous top limit of cells.
My question is that something I need to worry about, shouldn’t MPPT stop charging before that voltage is reached?
Did you program the mppt for your battery specifically? The preset may not be enough as each battery has its own settings.
It could be that the bms is disconnecting in self protection.
Does the mppt read the battery voltage correctly?
I will have to check next week battery voltage from MPPT and battery specs when i go to seaside.
I think that BMS did disconnect but shouldn’t mppt cut charge before that voltage is measured not letting the BMS to kick in?
If there is an unbalanced cell in the battery with a higher voltage than the other cells the BMS can shut down before or while the total battery voltage is 14.2V, the MPPT absorption voltage. When the BMS disconnects the MPPT takes time to respond and can give a voltage spike above the setting. You need to
- Confirm if the 15.2V occurred during charging or on BMS disconnect. It is no good just looking at the max recorded voltage.
- Hopefully you have a Bluetooth BMS so you can check cell balance.
Thank you for replaying. Unfortunately, the 12V battery is not Victron; it is a cheaper battery with internal BMS. I am not able to check each individual cell voltage or how much they are unbalanced, if any, but I will try to check what disconnects (BMS or MPPT) will be hard, though, to be there at the exact time.
SO what would be the problem/difference if MPPT disconnect charging or BMS does, i guess MPPT should kick in before BMS
If the battery is well balanced the MPPT should stop charging first because it is set to 14.2V and the BMS overvoltage should be higher. However as stated a poorly balanced battery can stop first. Often on cheaper batteries when used for the first time it can takes several charges to get them in balance with BMS shot downs.
that is what was strange to me why MPPT didn’t stop at 14.2, so how come max battery voltage was able to get to 15.2V (i am only charging with MPPT).
Where did you find out about the 15.2V, was is on the daily overview quoting max and min voltages or did you see this on the live data or on the historic trend when amps were flowing into the battery.
in my Victron shunt histroy tab, I did reset the history and checked few days later again I saw 15.2 as max battery voltage
As I tried to explain above, if the battery BMS has disconnected the voltage can jump up so just looking at the reported max voltage can be misleading. You have to either plot the voltage trend when it is charging, or read the value while charging.
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