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geomz asked

Functional purpose of voltage sense wires?

Can someone shed some light on the intended functional purpose of the Voltage Sense wires on a Multi/Quattro?

Are you using it? If so, how/why?


The manual says loosely that it's "to make up for voltage losses across the wires".

With the volt sense wires connected or not connected, under minimal load or loads in excess of 100A, I've never seen any change in the reported voltage by the system.

This was true even before my installation of a BMV (with the lithium batts) and still so now, since SOC and voltage readings (I assume) are now coming exclusively from the BMV.

The voltage reported (by the BMV) is within .01 V of the voltage reported by the BMS on the batteries with minimal load, and within the expected 2-3% difference under heavy loads.

I'm using 2/0 (70ish mm cross section) wires and runs are around 10-13 ft to the batteries. The BMV is 5-7 ft to the shunt. 24V lithium system.

The lead-acid system prior was considerably sloppier, although still using 2/0 cable, and I still recall no differences.

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ben avatar image ben ♦ commented ·

They're important in my system, because there is definitely voltage sag under load.

Where are you looking when you describe seeing "reported voltage"? Victron systems report different voltages in different places, and it can also change depending on what options you elected in the software.

The quickest way to determine if you have any sag (and I suspect you probably do, at 100A with 12ft of 2/0 and presumably at least one fuse and contactor) is to take your multimeter and probe the batteries and then the DC input terminals of the inverter directly. Do so while the system is under a continuous, heavy load, and let us know what you find.


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Paul B avatar image
Paul B answered ·

Keep in mind that the volatge sense also increases the charge voltage by the volt drop so that the batteries get the corrected volatge for charging

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benl answered ·

This is 4-wire sensing aka Kelvin sensing, a basic electrical measurement technique.

https://en.wikipedia.org/wiki/Four-terminal_sensing

Whether it makes a practical difference in your setup is dependant on cable size and current load, as others have noted. Unless you've massively over-sized the cable it would be a worthwhile thing and provide improved regulation.

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rjoustra answered ·

Do you have to enable voltage sense somewhere. I am still seeing the inverter voltage reading on my cerbo not the voltage sense wires I installed based on reading I am taking at the inverter and at the batteries under load.. I installed them on my L2 inverter in a split phase system would I need to install them for both or move them to the L1 inverter?

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neeyee answered ·

I have this same scenario where I have attached the voltage sense cables to the indicated + and - terminals and the voltage reported by the Multiplus did not change or improve.

This is a standalone install of Multiplus 5kva with 400Ah of batteries - there is a delta of 1.2v between battery voltage reported on Ve Configure and measured by multimeter at the inverter and battery terminals. Measuring at the inverter terminals vs battery terminals using a multimeter shows a 0.1v difference so clearly there is some sort of internal calibration issue with the Multiplus

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ludo avatar image
ludo answered ·

I have exactly the same problem on my 12/3000 unit, seems to be "systematic".


pls. Victron, do something for us ;)

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ludo avatar image
ludo answered ·

OK, so i now checked some things, changed battery from "individual" to LiOn, set charge current to 120A and send the settings to the MultiPlus.

BUT, this time (for the first time) i didn't send only the modified, but ALL settings.


Now my AC-current limit is working, AND my DC-sense- wiring is working.

Thanks for nothing, Victron.


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