openinverter forum

Hello everyone. Hope you are having a good week so far.

I could not find this addressed elsewhere, but I am experiencing a deviation between the ORION 2 BMS Pack SOC / Voltage and the UDC reading on the OI charger software.
I had set the ucdlim at 340 based on the concept that my top voltage was around 340V (84 cells X 4V). I could raise this number of course, but the bigger issue is that the UDC reads 343.4 right now and the ORION BMS reads 331.9V (77.5%) and I am not sure what would cause the two numbers to be so far apart. I assume they are getting their information from the same place. I also assume the ORION would be more reliable to use as the actual voltage since I am getting readings from every cell. I am not using CANBUS with the V5 card.

I do not see a way to offset the UDC number like we can in the inverter firmware, but wondered if this is possible as well.

Would love to know anyone's thoughts.

you have 20A flowing into the pack, depending on your wiring there will be a voltage drop.

Worryingly your Orion is not indicating this current going into the pack.

Hi Tom. Thanks for the reply. No need to worry. When I took these photos, the charging had stopped because the UDCLIM was reached, so the approximate -20A is not showing but it does show up when charging. I had not refreshed the page on the left for the OI firmware so it was still showing the amps when charging.

Does that mean that the ORION is accurate and I should raise the UDCLIM to 350 or something like that so the charger does not turn off prematurely?

The Orion is accurate of course as it counts the cells. You need to ensure the Orion can stop the charging when it is unhappy or thinks the pack is full.

My delta between Tesla Gen2 charger and BMS voltage is usually around 3 volts. 10 volts is a big difference. If you lower the charge current do the voltages get closer together? That would indicate you have extra resistance somewhere, 10 volt drop at 20 amps would mean that there is 200 watts being dissipated somewhere!