BMV smart shunt tail current setup

DIY
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1

Hello,

In my current setup I have a BMV-712 Smart monitor and I am planning to expand my battery bank from a 1x 250 Ah gel battery to a 2x 300 Ah LiFePo4 in parallel connection (600 Ah total). The tail current for the single lithium battery is specified by the manufacturer to be 15A per battery which is 5%. In case of the parallel connection that sums up to 30A total tail current for the bank. All my Victron chargers are rated at 30A max charging current (1x MPPT 100/30, 1x Orion Tr-Smart 12/12-30, 1x Blue Smart IP22 12/30) which means that in normal case the battery bank will be charged with the equivalent of the tail current, or even less. How should I a set the tail current percentage in the BMV setup to get a correct reading when the battery is full. I am afraid that I will get false readings for 100% SOC of the bank in case the low charging current.

Thanks in advance for the hints

2

There are 2 settings, charged voltage and tail current. Make sure that the charged voltage is set 0.1V below the absorption voltage used on your chargers. If the chargers are 14.2V then set the BMV to 14.1V. The charged voltage is critical in this case with a low charge current as the battery voltage will stay at 13.5V for most of the charge, only rising when it is very close to full. This means even charging below the tail current, it is basing the choice off the voltage. This is how lithium behaves differently to lead acid.

I have 600Ah lithium, tail current for mine is 4% so 24A. I charge from engine alternator at 100A or inverter charger at 90A or solar at typically 10- 25A and the shunt settings with the 0.1V offset work fine with the low solar charging.