I have a BMS 12/200 controlling x3 330Ah Victron Smart Lithiums. The Multiplus is connected to the BMS via Inverting Remote on/off cables and we are not using the System+ Port to run the Multiplus. There is a Cerbo GX in the system as well that is communicating with all devices via VE Direct/VE Bus. Charge Controllers are controlled using Smart Battery Protects.
The issue we are having is that the Cerbo is showing very strange surges on AC and DC Loads when an AC load is turned on.
Example: a ~1kW AC load is turned on, and the AC load shows anywhere from 300W to 800W meanwhile DC loads are constantly switching between +600 and -600W.
I will upload a video to YouTube shortly. Does anyone have any thoughts as to why the DC and AC loads are so sporadic?
If that is a variable intensity heat gun, those can do nasty things to the AC waveform.
Can you turn it all the way to maximum power and see if the problem persists?
The battery power draw seems to be stable while you’re running the heat gun so indeed very strange as to why the DC Load would jump up & down like it does.
Last I remember the “DC Load” is a calculated value by measuring what goes out of the battery and into the Multi.
Yeah that is my understanding as well. We tried replacing the Cerbo to see if the unit was calculating it wrong, but that didn’t do it. Tried Zero Current Calibrating the BMV, triple checked AC wiring etc.
I even tried old firmware on Cerbo and Multiplus and all new firmware.
If the heatgun was running 100% full throttle and not being PWM pulse-heated, it’s a strange issue.
Cos phi can’t be the culprit as a heatgun tends to be a purely resistive load.
Should there be pulse-heating after all (test with a bigger room heater perhaps ?) then the issue could be caused by different field update timers.
Not stupid at all! Gotta for those 'i’s and cross those 't’s.
But yes I do have a DC system.
I was suspicious of that for a minute because from the System+ Port I connected to a bus bar where the Two Charge controllers land and the DC System lands. The charge Controllers do go through SBP before the bus bar, and since the System+ port has discharge and charge protection I figured this would work.
Also, in that video, solar is turned off, so even if that’s not ideal, in the example in the video it was turned off, so I don’t think that’s the issue.
Have a read of FAQ Q6 in the troubleshooting section of the Cerbo GX manual. I quote one bullet point below.
The Multi does not really measure the power being drawn from the battery. It measures the current at the output of the inverter, and then makes an assumption of the power being drawn from the battery.
Therefore, if the multi is having trouble measuring the ac loads (for reasons I can not explain) then the calculated DC taken by the Multi will also vary compounding the DC box errors. The key is watching the battery current. If knowing DC loads is important, for example with DVCC and managed batteries as in my case, fit a SmartShunt on the DC loads as a DC energy meter type “DC System”.
Thanks for the heads up. Yeah, I knew the Multiplus didnt have current sensor for DC Power, but its just strange to see these readings. We have done multiple systems like this and never had this issue.