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I have installed a new BMV-712 on my camper that has 2 x 12v 115AHr AGM's in parallel. I also have a separate Volt/Amp meter installed. The BMV reads current lower than what it actually is. 3-5 Amps on Charge and Discharge. 10mm cable used to connect the shunt?
I have no idea if the BMV is just not a very accurate device or how to investigate the problem
The unit is definitely a lot more accurate than 3-5 amps, so something is wrong.
Please take some photos of your installation and post them, it might help to diagnose.
Also, how do you know it is the BMV that is giving the inaccurate reading, and not the other measurement device?
In addition to Guy's comments, did you perform a Zero current calibration when there is actually Zero current flowing?
This device should be very accurate. If it is not, then something is wrong.
@RynoRBO Please post photo's of the installation of the Shunt, this might help solve the issue.
The reason I am trusting the DB reading is because it has a 12Amp charger inside
The picture and description with the shunt has me thinking.
I assume that the two wires between the battery and the shunt are just in parallel and go to the same battery terminal?
What does concern me is that after the shunt you say one wire goes to the DB and the other one goes to chassis. What this means to me is that there are now two different current paths for each shunt. The BMV shunt can have current from the DB and from chassis return to battery (current that will have bypassed the shunt tin the DB).
If you have two shunts then they need to be in series with one another with nothing branching off in between them otherwise they won't be measuring the same circuit.
The botom 2 wires comes directly from the -Neg of the 2 battery terminals
According to the Victron installation guide nothing other than the -Neg battery terminals must be connected there.
You make a good point on the chassis earth. I will have to investigate the potential of different paths
Your comment is quite a brain tease... What if I disconnect the chassis earth? Then the load cable goes directly to the -Neg of the DB board only.
That should eliminate multiple paths.. right? Even if just temporary to prove the point...
PS: The Camper was wired by the manufacturer. I just added the monitor
Some thoughts / recommendations;
1- Are BOTH current shunts positioned / wired directly to the battery terminals BEFORE ANY connections to loads or charge sources?
Or is the shunt related to the display that's reading higher current positioned / wired to / near the output of the charge source?
2- If both current shunts are positioned / wired on the negative side / cable, are they wired in SERIES?
3- Have you tried to PHISICALLY disconnect the wiring from all other loads & circuits (except the charger), then check the readings? (This test should prove/disprove a wiring issue with the 2x current shunts)
4- Do ALL devices / circuits in the system have a proper negative cable / wiring all the way back to the current shunts? (NOT just earthed to body / chassis & using that as the negative)
5- There have recently been a few BMV issues related to the UTP cable. You could try to slowly move the cable around near the connections on either end while watching the BMV display to see if anything changes.
6- Probably unrelated & I don't know what your max system current is, but 10mm2 wiring is very small for main battery cables. I would recommend at least 35mm2 as a minimum for most systems
7 - Lastly, if everything checks out OK, as already mentioned, there is a good chance that the BMV is the unit that reading correctly & not your other reference...
Good luck, Mark
1 - Yes the 2 Battery terminals are connected to the Battery screw on the shunt, other side is the Negative Ground and going to the DB Board
2 - I have only one shunt
3 - Low readings are in sync the higher it goes the bigger the difference
4 - Hmm I want to say yes
5 - The volts are completely in Sync, its just the Amps
6 - Wow 35mm , okay I suppose it can be the thickness, but would I not also see a voltage drop as an indicator. also note the cable is only 100mm long
7 - Good point - I would have to get a multi-meter and do another comparison
