I’m trying to understand why SOC would reset to 100% when the criteria isn’t met. This is a 920ah LifePO4 bank charged to 14.2v. While still charging in excess of 60 amps, voltage at 13.5 I see the BMV reset to 100%. When I start the charge if I’ve pulled 300a out once it has counted 300a in the SOC automatically goes to 100% regardless of the current, voltage, etc. The charging is still in bulk mode, hasn’t even entered absorption.
4% tail current would be 36.8a but it’s always way higher when it sets to 100%
See attached screen capture of battery monitor settings.
If it has started at 100%, pulled out 300Ah and recharged 300Ah then of course it will read 100% again, this is how it works, by counting energy in and out. The synchronisation settings are to make it go to 100% if the battery gets full when it is displaying say 90%. You need to ignore the SOC for the moment and carry out a full charge right through absorption to float then the 100% will be correct. Batteries often arrive at 40-50% so the initial SOC is wrong. You need that absolutely full charge to float to get everything aligned.
The other explanation is incorrect wiring of the shunt. See
Thanks for the response. I’ve had many cycles to 100%, manually forced synchronization at 100% again (after battery stops accepting current) and performed a zero current calibration. The wiring is correct, all negative loads come off a bus bar and the load side of the shunt connects to the bus bar.
When charging, battery will be at 94% for example and shunt will already be at 100%. It’s like it’s not counting properly on the discharge. The gap is closer when cycling down to say 40% in one day and charging back up to 100% but if they sit at 60% charged on lower float voltage for a week the gap gets larger and larger. In the 300a current case, 350-360 actually went into battery but shunt was 100% at 300a.
Thinking to try raising peukert up to 1.06 or 1.07 and see.
The other.one is reducing the charge efficiency so it does not count up.as fast.
What type of batteries, could there be a high parasitic load in the batteries (BMS, Bluetooth, heaters, failing cell, short circuit, ???) that is taking current out of the batteries but not being measured. I know that you are seeing an offset that is much larger then a BMS current.
The other thing is a zero current calibration to make sure it has not developed an offset.
Lifepo4 batteries. The MP is being controlled by batteries BMS. The float voltage is 13.5. If I cut the voltage back in DVCC on the Cerbo to a lower voltage, 13.3 for example, the problem gets worse. I think you hit the nail on the head, the bms is using current that is not seen by the shunt. I din’t think about that…
Comparing the SOC from the BMV and from the BMS will always give different readings because they are working differently.
I guess most BMS ignore the Peukert and/or the charge efficiency.
