Voltage differences between SmartShunt and Multiplus2/MPPT

Q&A and troubleshooting
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1

Hi everyone!

A quick overview of my system:

  • 3x Multiplus 2 48/5000

  • 4x MPPTs connected via VE.CAN

  • Cerbo GX

  • SmartShunt 500A

  • 16 LFP battery cells without a connected BMS

  • No DVCC configured

  • AC and DC excess feed-in

  • Everything connected to AC-in including a Fronius inverter

  • 54.9V absorption, 54V float

I have the issue that the voltage measured by the SmartShunt is always slightly lower (0.1–0.25V) than the voltage shown by the other Victron devices (MP2 and MPPT).
The MP2 even shows a higher voltage when discharging.

I borrowed an additional SmartShunt and connected it at various points in the 48V system: on the busbar, at the MP2s, at the MPPTs, and even tested it without a fuse.
This SmartShunt then showed about ~0.03V more than the installed one.

The lower voltage itself does not really bother me, but apparently it is not used for control in the MP2. So what is the “battery monitor” setting in the Cerbo actually used for? (is set to the shunt)

Because of this, I have the problem that when 54.9V is present at the MP2, the shunt only shows about 54.7V, and the MPPTs go into float mode and drop to zero power, even though AC + DC excess feed-in is configured and the feed-in limit has not been reached.

Does anyone know this issue, or what do you think about it?

Best regards,
Stefan

2

MP2s have a Vsense input, use it. The 0.2V are simply voltage drop over the cables. By using the Vsense you can compensate that.

Instead of moving arpund another shunt you could also use a multimeter to measure voltages across different points

1 Like
3

I have also thought about using the Vsense input, but have not implemented it yet.
This is not a voltage drop across the cables, because in that case the voltage at the MP2 would be lower than at the shunt, but it is not, even during discharging.

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