I built a DIY battery with Eve MB31 cells and Jk bms V19. Everything works correctly (connect VE can bms without packet loss, bms is set master on battery monitor and DVCC).
On bulk everything is fine (charging amps are corresponding with reading from BMV-712).
The problem is when it goes into absorbtion and decreases the charge to 20a. This is where it starts discharging and charging every few seconds. On the bms it shows that it charges or discharges with 20A, in reality through the shunt the current is almost 0.
Maybe someone has experienced this problem before and can help.
Don’t trust JK current measurement, use a proper shunt.
Reason of the incorrect current is the way JK measures the current.
They do measure peek current and not average DC current.
The current from and to Multiplus II isn’t DC there is a AC component on it (specially in on grid mode there is a lot of AC)
Specially at low currents this gives a measuring error, this is also the reason why SOC is incorrect.
There’s also a small voltage difference between the devices, have you measured the voltage or calibrated the JK BMS. Maybe just set the JK voltage to match the shunt? That might help with the charging/discharging.
The current is probably correct on the BMV and you can either try to calibrate the JK BMS again or ignore it. If you have a clamp meter you can verify.
The voltage difference is normal. It has a small voltage drop on the cables (between bms and Smart shunt). Anyway you can’t set perfectly because there is a small variation (lag) between what you see from vrm or Bluetooth on the phone connected to the bmv and what is real on the bms. With the voltmeter connected, the voltage has an error of 0.1V maximum.
Thanks for the advice but I don’t think this is the real problem.
There is a >0.1V difference visible in your screenshots. Even if there is a small voltage drop it might be better to try and match them. DVCC probably uses the voltage from the shunt. I’ve had 0.2V difference make the battery charge/discharge instead of idle.
Theoretically, DVCC should use the data from Jk. At least I believe so
I tried to disconnect the bmv for the same reason. The behavior at bms is the same. Charging /discharging on absorption… Even with master data from bmv, still same issue.
