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karelholubicka avatar image
karelholubicka asked

MultiPlus voltmeter discrepancy

Hi, I am seeing unusually big difference between voltage reading on Multi vs SmartShunt+MPPT. On all my other systems, this difference is usually negligible (0,1V on 24V system) according to voltmeter accuracy. But on this one it is 0,5V on 12V, actually 10x bigger. BMS reports exactly same voltage as SmartShunt and MPPT, so I suspect voltmeter on Multi simply being 4% off - too much. Does anyone have similar issue? I can not go to DVCC to bypass it. This Multi 12/3000/120 otherwise runs happily, is properly connected directly to the battery over 500A fuse and switch and voltage drop can be considered none for currents below 10A.

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MultiPlus Quattro Inverter Charger
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4 Answers
klim8skeptic avatar image
klim8skeptic answered ·

@KarelHolubicka Hi, I am seeing unusually big difference between voltage reading on Multi vs SmartShunt+MPPT.

I used to see similar discrepancies with my system with my multi due to less than optimal voltage drops when under high loads/charging.

My solution was to hunt down the connections that were causing excessive voltage drop, and then to apply DVCC to my system so all devices were acting on the most accurate voltage reading (BMV).

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karelholubicka avatar image
karelholubicka answered ·

I see the discrepancy under (almost) no load - see the graphs. And DVCC is not an option to me due to used battery BMS. Thanks anyway.

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dognose avatar image
dognose answered ·

What is your wiring like? (Diameters and lenghts on each device?) Voltage drop may be a result of unsuitable cable sizing.

Also Fuses range around 100mV voltage drop as well.

As per documentation the MP is able to compensate a voltage drop of up to 1V, you may wanna setup voltage sensing as of the documentation to simply let the multiplus compensate?

4.4.5. Voltage sense

For compensating possible cable losses during charging, two sense wires can be connected with which the voltage directly on the

battery or on the positive and negative distribution points can be measured. Use wire with a cross-section of 0.75mm² (AWG 18).

During battery charging, the MultiPlus-II will compensate the voltage drop over the DC cables up to a maximum of 1 Volt (i.e. 1V

over the positive connection and 1V over the negative connection). If the voltage drop threatens to become larger than 1V, the

charging current is limited in such a way that the voltage drop remains limited to 1V.

See Appendix A, Connection overview [32] for the location of the connector.

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karelholubicka answered ·

Hi guys, thank you for your input. However, I need someone from Victron to comment this, please, if this is common error. I will call the distributor next week anyway. I understand that bad wiring is the usual cause, but I am asking here just because this is NOT the case - difference happens even with 0A current (see logs), not mentioning my cables are 0,5m of 2x2x50mm2, which is pretty adequate even in full load.

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Justin Cook avatar image Justin Cook ♦♦ commented ·

This is not a Victron Support channel, the Community is staffed by volunteer experts and other owners and enthusiasts such as yourself. For official comment, your distributor will be the best source of information!

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Alexandra avatar image Alexandra ♦ Justin Cook ♦♦ commented ·

Big wire + bad cramps still = volt drop. Sorry, have seen it and had the argument with the installer.

Also had one clamped on the heat shrink. Not by much but enough.

Bad torque also yes. (And by seasoned guys.)

But DVCC negates the problem even without can bms since you have a shunt which is likely set as the battery monitor for the system.

If you feel the equipment is defective - return for a warranty claim check.

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