Victron BMV-700 Readings Seem Inconsistent

January 13, 2022, 06:21:28 pm

Hey gang, I am looking for input or thoughts on what seems to be odd readings my my Victron BMV-700.

I think I have figured something out that has been bothering me for some time. At some point prior to my purchase the inverter/charger was replaced with a Victron MultiPlus 3000. In addition a Victron BMV-700 and Victron Color Control GX were installed. My issue is that the BMV-700 reads a declining charge % over time even when the coach is plugged into shore power and the inverter/charger goes through the normal charge steps and gets to "float" in what seems to be an appropriate amount of time.

I know I should test the batteries with a multimeter, but I haven't gotten around to that.

I have been tracing wiring, looking at the wiring diagram in my owners manual and comparing that to what I see in the coach. The one thing that jumps out to me is that the shunt was placed right above the MultiPlus. When I look at the wiring diagram in the owners manual it shows two cables coming off of the negative post of one of the batteries of the coach battery bank. One cable cable goes to the inverter/charger and the other to, what I interpret as, a coach ground.

So my interpretation is that the seemingly specious readings on the BMV may be driven by the fatal mistake of not having the both cables connect to the load side of the shunt and a single cable going from the battery side of the shunt to the battery bank.

Does that make any reasonable sense to any of you? Would that reasonably be giving specious readings?

The other odd behavior on the BMV, and I don't have any logic explanation yet, is that the BMV may be reading a low level of charge, but the coach has been plugged in, the inverter/charger is in float mode, but after starting the engine the BMV almost immediately reads 100% state of charge.

The other installation issue that seems odd is that there is no VE Direct cable going from the BMV to the Color Control GX. The Color Control GX appears to only be connect to the inverter/charger via the VE Bus. Assuming the BMV were working correctly and the shunt was in the correct place, wouldn't a normal installation have the BMV and Color Control GX connected to each other?

Re: Victron BMV-700 Readings Seem Inconsistent

Reply #1 – January 13, 2022, 08:37:54 pm

The shunt should be on the negative side and all ground cables need to be on the opposite side of the shunt from the battery.

Re: Victron BMV-700 Readings Seem Inconsistent

Reply #2 – January 13, 2022, 11:10:32 pm

I have a separate bms on each lithium battery (2 total), a BMV-712, and a xantrex inverter and they are seldom in sync with each other on SOC or amp hrs used or remaining.

This is the reply I received from Overkill Solar who sold me the BMS.

"Hi Tommy,
I took a look at my Victron setup and see the same issue/feature, I haven't tried to address it but will now. I did notice in the Victron app there is a manual "Synchronize SOC to 100% " so next time my batteries are at 100% (based on the XiaoxiangBMS App) I am going to hit the Synchronize button. On the BMS the SOC (XiaoxiangBMS App) 100% is reset when the cells get over 3.5oov on average (so 14.0V for a 4S battery) I think I will have to repeat this process every so often as the readings slowly drift apart.

If you are successful in synchronizing these apps let me know how how you did it. "

Open to explanation or suggestions!

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