Victron BMV-712 Smart reading approx 50% actual charge current

[nickburt]

I'm having an issue with the BMV-712 Smart reading approx. 50% charge current, when compared to a (known good) clamp meter reading.

See my (very rough - sorry) schematic. The BMV is reading around 4 amps when the mains charger is on and the aux batts being charged via the Orion 12/12-30, but if I put my clamp meter on the +ve output cable between the Orion and the Aux +ve bus bar, I get around 8 amps.

I know there are couple of "unconventional" methods of connection, but, in theory, these shouldn't make a difference to the way the BMV shunt reads the -ve loads. Unless I've missed something, all -ve connections, in around about way, pass through the shunt, with one exception: my winch -ve connection is excluded from the shunt, this is done deliberately to avoid high winch currents passing through the shunt and possibly overloading it.

The shunt is the one that came with the BMV - 500A, 50mV and the BMV has been configured for 240Ahr batts. All other settings as shipped.

Any suggestions please ................

 

[nickburt]

Just to add to this. The above test was done with all loads either switched off or disconnected.

 

[Speric]

I'm not an electrician, but I just finished installing my system last night so can kind of make out what you have here. Are your 2 batteries connected in any other way, like in parallel? or just via the busbar? It seems like you have 2 separate systems here. But take what I'm saying with a huge grain of salt. I was still pleasantly surprised my truck didn't burn down overnight. lol

 

[K12]

I had the same probelm with my BMV when i originally hooked it up and for the life of me couldnt figure out why. After Lots of trouble shooting I found the problem was the way the batteries were wired on the negative side. From your diagram it looks like this may be your problem as well. In order for the BMV to read the overal charge on the batteries they you need the negative of batt 2 connected to batt 1 then to the BMV shunt. From your schematic it looks like you have both negatives going to a bus bar then to the shunt. I had a similar setup and the shunt was reading battery 1 as the main battery, and subtracting the amps charging battery 2.

making it short. you are reading half the charging amps because its being split between 2 batteries. If you do ground pole of batt 2 connected to ground pole of batt 1, then run batt 1 ground pole to the buss bar it should eliminate the problem (at least it did on my setup)

 

[nickburt]

I'm not an electrician, but I just finished installing my system last night so can kind of make out what you have here. Are your 2 batteries connected in any other way, like in parallel? or just via the busbar? It seems like you have 2 separate systems here. But take what I'm saying with a huge grain of salt. I was still pleasantly surprised my truck didn't burn down overnight. lol

Yes, two systems linked, but the B2B charger is an isolated charger, so when not on, they are separated from each other.

Sorted the problem. Even though the winch -ve is connected to the battery side of the shunt and therefore should be counted in the BMV calcs, it was. The problem then was that the winch -ve was also connected to a common -ve bus bar also linked to the chassis, so some stray current passing through the chassis and not being accounted for by the BMV, hence the difference in current readings.
Not sure it should have affected it, but it did. Once I separated the winch negative from the chassis all was good.

 

[nickburt]

I had the same probelm with my BMV when i originally hooked it up and for the life of me couldnt figure out why. After Lots of trouble shooting I found the problem was the way the batteries were wired on the negative side. From your diagram it looks like this may be your problem as well. In order for the BMV to read the overal charge on the batteries they you need the negative of batt 2 connected to batt 1 then to the BMV shunt. From your schematic it looks like you have both negatives going to a bus bar then to the shunt. I had a similar setup and the shunt was reading battery 1 as the main battery, and subtracting the amps charging battery 2.

making it short. you are reading half the charging amps because its being split between 2 batteries. If you do ground pole of batt 2 connected to ground pole of batt 1, then run batt 1 ground pole to the buss bar it should eliminate the problem (at least it did on my setup)

That was my thinking this morning, but it turned out to be the winch negative also linked to the chassis at another negative bus bar up front. Once separated from the chassis all was good.
Not sure it should have been affecting it, but it was.