Hello,
I had to de-commission one of the 8 Pylontech US3000C batteries in my installation because it was always giving high voltage alarms, even after extensive balancing. This was a good opportunity to update all firmware and to install ESS instead of the old Hub assistant.
Now there is a big 6V difference between the voltage measurements from Pylontech BMS and Multiplus II 48/10000,
the Multiplus is measuring the 6V higher voltage. Before the Firmware update, the measurements were consistent though.
It is odd that Multiplus and MPPT charger now show all the time Absorption charging.
I believe it does not matter much because Pylontech BMS is configured as the controlling BMS.
Does anybody have a suggestion how to fix the Multiplus voltage measurement?
Maybe the hardware for the Multiplus voltage measurement is broken?
Best regards,
RaiBac
Was the measurement at the victron terminals verified with a meter? If not then that is a good place to start. It will help determine if the unit is becoming faulty or there is something else to investigate.
If you are using the ve bus as well, when it is processing power those readings are related to power movement. So the measurements need to be done with no load, no charge and no discharge.
Pylontec have an interesting method for determining voltage and sometimes the voltage it reports will not be what is measured with a meter.
This is a remote installation. I have no chance to verify that with multimeter measurements. But the difference is so giant, that the Multiplus Measurement cannot be right At this moment, Pylontech measurement is 52.2 V, while Multiplus II measurement is 58.2 V. At the voltage measured by Multiplus II, the Pylontech batteries would be shut down.
Then what is correct and what is not cannot be determined.
Or whether something has worked loose on terninals etc. all these things have to be physically checked when things donât look right in stats.
What sort of power is moving in the system?
Currently, the solar is slightly charging the battery and the Multiplus provides AC output for the loads.
How big are the loads?
when the ve bus is processing power it is not unusual for the voltage to read higher there, even if the battery is not being charged. (The system does this to make the dc bus in the inverter the place where power is being used from over the battery as source)
If the Multiplus II would measure lower voltage, then this could be a voltage drop due to the cable connection. But the Multiplus is measuring the higher voltage. Am I right?
Very small loads for the moment: Solar yield 364W, AC load 280W, grid 50W.
Not in every situation.
This is why the testing of voltage is done in various operations.
Pylontec dont actually measure their battery voltage. They have an averaging type set up. So if the batteries are unwell this could be incorrect.
Independent measuring is important. It is how faults auch as a lown fuse or loose terminal or other problems are determined.
Understood, but actual multimeter measurements are only possible in a few months from now.
The Pylontech batteries were always healthy, except one of them which I have disconnected and switched off now.
If the batteries arenât being overcharged and the system is behaving correctly otherwise then there is not much to stress about right now.
With the current Multiplus II voltage sensing, the batteries would not fully charge except from solar MPPT,
because the solar MPPT have their own voltage sensing.
Proof that the Multiplus II voltage sensing is broken:
- Voltage read from Pylontech BMS is 49.63 V.
- Voltage read from Pylontech BMS is consistent with single cell voltage.
Lowest cell voltage 3.224V, highest cell voltage 3.324 V.
Sum the 15 cell voltages â ~3.27 V average Ă 15 â 49 V
- Voltage read from MPPT 1: 49.77 V
- Voltage read from MPPT 2: 49.75 V
These voltages are all consistent. There is no voltage drop involved anywhere, the voltage reading was done at zero charge/discharge current.
These voltage reading are in contrast to the voltage reading from Multiplus II: 55.34 V
Setting Pylontech BMS as the controlling BMS is not enough.
SVS would route the accurate BMS voltage to all chargers (Multi and MPPTs).
However, SVS is forced off in DVCC with Pylontech in Venus OS 3.73.
There may be a small risk of voltage overshooting with SVS because the Pylontech BMS reacts too slow,
but that would be negligible as compared to the wrong Multiplus II voltage sensing.
I am somewhat lost on how to proceed from here.
I have ticked âDisable Vsense (for diagnostic purposes)â in VEconfigure and uploaded the change.
This has fixed the wrong Multiplus II voltage reading.
Voltages before the fix:
Multiplus II: 57.62V
Pylontech: 51.65V
After the fix:
Multiplus II: 51.68V
Pylontech: 51.63V
To my knowledge, I had Vsense not connected at the Multiplus II.
From the documentation of Multiplus, it seems not mandatory to connect Vsense.
I am happy that the voltage sensing seems to be corrected now.
It seems there is some mistake or at least some missing part in the Victron documentation.
Seems pretty straight forward.
You donât have the v sense wires attached so it is not a used feature. Box doesnât need to be ticked.
Yes, this is what I thought.
Without ticking the box, there is the Multiplus II sensing error.
Only after ticking âDisable Vsense (for diagnostic purposes)â, the sensing error is gone.