Victron Multiplus II (8/5000 - DC Voltage calibration - 0.3V deviation detected

DIY
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1

I have detected a different measurement when mettering the DC voltage in the multiplus II. In this example there is no DC current, so 3 voltages should be the same:

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The DC voltage detected in the BMS is aprox equal to the DC voltage detected in the “Lynx Shunt”, but is is not equal to the one detected in the Multiplus II.

At this moment I have solved the issue applying a 0.3V increase to the limits. For example; RCV: from 55.2V to 55.5V. But I do not like this solution. Is there a way to callibrate the voltmeter in the Multiplus II system?

Many thanks

2

Short answer: no.

There is calibration data, but Victron don’t (want to) provide access and modification of this info, unlike other inverter manufacturers.

3

The real question is, when tested with a DMM is the terminal voltage at the MP2 terminals correct or not?

There does have to be some potential to create a charge and create flow.

4

Indeed, normally they are pretty well calibrated.
For example, on my system, the voltage differences between the Multi RS, the BMS and a pretty good multimeter are all within 20mV.
Also the cable sizes and various connections, switches and fuses play a big role on voltage drops.
The voltages order of magnitude for the given current flow (charging) is correct: 55.52V (MP2) → 55.28V (Shunt) → 55.18V (BMS)

5

Sorry for the delay, LX. This weekend I have got measurements with a 99% of charge, and I=0.00A

Here the readings with 2 DMM:

IMG_1973
IMG_19733744×1738 1.97 MB

“DEVICE” column is the reading in Home Assistant.

The readings at MULTIPLUS1 and MULTIPLUS2 have been taken at the MP2 DC input terminals.

I think there is some deviation in MP2 voltmether readings, isn’t there?

Many Thanks

6

There can be many reasons for it.
0.25v difference,yes. There is less than 1% difference. Again. How to great power flow in directions needs potential? Hmmm

A simple example is when you set the system to feedback to grid at 100% the MP terminals will rise 0.4v above to do so.

As a further thought the Victron is not a calibrated reading instrument. The shunt is a bit different and you can see that is closer to what you are expecting.

It is within acceptable deviation between meters. Compared even with the two readings between the two different digital meters you used. (Which are supposedly calibrated devices).

7

I have had the same problem from installation 2 years ago. I have a second MPPT now installed which gives correct readings of battery voltage, but the main system is around 350mV too low. I have had to add 0.35V to all the levels to get correct battery voltage readings at the batteries. It is not to do with loads and connections as some suggest, as with yourself, a calibrated meter proves the voltage is reading incorrectly. If this is adjustable in software, why won’t Victron allow us to change this calibration?

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