Victron Monitor Question

[eric1514]

Just a quick install question.

I’m going to use the +B2 terminal on the shunt to check the voltage on the chassis battery. The instructions say to run a wire from the positive terminal of that battery to the shunt terminal +B2. I got that. That’s how I wired up my Trimetric in my van. But then it says to run a wire from the negative post of the chassis battery to the load side of the shunt.

My question is why? I didn’t do that for the trimetric and I can’t see what that adds.

TIA,
Eric

[booster]

Originally Posted by eric1514

Just a quick install question.

I’m going to use the +B2 terminal on the shunt to check the voltage on the chassis battery. The instructions say to run a wire from the positive terminal of that battery to the shunt terminal +B2. I got that. That’s how I wired up my Trimetric in my van. But then it says to run a wire from the negative post of the chassis battery to the load side of the shunt.

My question is why? I didn’t do that for the trimetric and I can’t see what that adds.

TIA,
Eric

Are any of these wires tied back to the monitor itself? It sounds like they are trying to isolate exactly the shunt voltage, perhaps to get accurate watt usage?

[eric1514]

The monitor connects to the shunt with a phone cable. There are no extra wires to the monitor. The connection to the monitor would be the same if I was using +B2 to read house battery temp instead of chassis battery voltage.

Ands it’s funny. Their diagram in the quick start guide shows this negative connection to the shunt from the chassis battery as some big honkin cable, not a thin wire like the positive connection.

[eric1514]

Here's a quick photo of the diagram

[booster]

I just looked at the diagrams for the Victron monitors. Since B2 is the second battery I think they are just tying the negative of the starting battery to the negative of the chassis and the charging systems to get an accurate voltage reading of the chassis battery. They grounds should be one reference, but it is very common for the chassis ground from the the chassis battery and/or engine and alternator to be of some significant resistance. This is likely what they are addressing, I think.

[eric1514]

Would I be OK just running a small wire to a spot on the chassis?

[booster]

Originally Posted by eric1514

Would I be OK just running a small wire to a spot on the chassis?

Probably, depending on where any resistance might be. If concerned, you could just run down the batteries and charge off the alternator and check for voltage from the chassis battery ground to the coach battery negative connection. You should see very low voltage if any.

[eric1514]

OK, thanks. I just mainly want to know if the chassis battery is getting charged when I plug in, or run the generator or the sun's out. I don't need super accurate readings like I want from the house batteries.

[Nic7320]

The load side of the battery shunt is at chassis ground for both batteries, so Trimetric probably assumed it's already connected.

Victron is either making sure you have an accurate reading by providing a better connection with another wire, or they may be using the black wire as a negative reference for a differential measurement (B2+ to B2-) and not using the chassis path.

Either way, it's done for more accuracy. My guess is they use the second method, commonly called a 4-wire measurement, so any charging or discharging currents in the main wiring to the battery won't affect the reading for the battery voltage measurement.

[eric1514]

Originally Posted by Nic7320

The load side of the battery shunt is at chassis ground for both batteries, so Trimetric probably assumed it's already connected.

Victron is either making sure you have an accurate reading by providing a better connection with another wire, or they may be using the black wire as a negative reference for a differential measurement (B2+ to B2-) and not using the chassis path.

Either way, it's done for more accuracy. My guess is they use the second method, commonly called a 4-wire measurement, so any charging or discharging currents in the main wiring to the battery won't affect the reading for the battery voltage measurement.

Thanks, Nic. I'll probably start by not supplying an extra ground and see how that goes. I'll check what the monitor says vs. what my volt meter says at the battery a couple a times a day and go from there.