My BMV-702 is showing a voltage that is about 5V low as measured with both my charge controllers and a voltmeter. It is also giving me top / bottom balance alarms (was set at 2% raised to 3% still happening near top of charge,) but when I put a meter on the bank the top and bottom are the same voltage.

Full disclosure, I'm pretty sure I do have one bad battery (4 12V in series - 48V bank) and there are 2 HA-02 balancers on the bank.

Other functions of the 702 seem to be accurate. Amps in and out and SOC look good.

Thanks

Edited October 14, 20214 yr by stuvo

I've changed both the b1 and b2 inline fuse holders and replaced the fuses with new 1 amp fuses. This did nothing to fix the erroneous voltage readings on the BMV-702. The voltage readings are even more inaccurate. I cleaned the dust out of the shunt. This did not help. My 702 is basically worthless except it seems to accurately track amp hours in and out.

I could post a series of pictures, but it's wired correctly. The meter worked beautifully and accurately for about 3 years. I haven't changed anything it just started giving false top / bottom alarms a few months ago. I would get out the meter and there was no difference in top / bottom battery bank voltage. That was when I noticed that the bmv voltage did not match the voltage shown on my charge controllers or my multimeter.

At this moment, the bank is floating at 56V. The bmv says it is 47V with a 3% difference between top and bottom. All 4 batts are at 14V as measured with a multimeter.

 

 

Reviving a very old post. Has anyone else ever come across this? 

 

So i have set out to get a shunt going to get more accurate battery SOC readings. 

 

A very nice gentleman gave me a BMV702 to test/try. And if all works i can compensate him. 

 

So. The unit shows lower voltage. What i have noticed, if i put the screen backlight off. Then the voltage is closer to true voltage. But still 2v off. The amps also doesnt make sense. If i set the BMV to the correct shunt size. Im drawing 100 x more amps than reality. 

 

If i change the shunt size settings. It gets closer to reality. And freezes on 7 amp draw. 

 

Ive been away from home for a couple of weeks. But will be home by Friday. And want to tackle this situation. As home assistant emulated BMS is either way off. Or my battery capacity is not a true 2.5kwh. But closer to 1.7kwh. Been playing with that to get the SOC to resemble something close to what the low voltage back to grid is set to.

 

The Victron cable between shunt and display is not the original Victron cable. 

Buying a new OE cable. Aswell as VE direct cable for a possible faulty unit doesnt make sense. 

 

Im asking the following:

1. Advice/opinion

2. Someone with a Victron BMV in centurion area that i could perhaps bring the unit and test on your system to determine if its a shunt/display or cable issue.

3. A shunt that i can use with the Solar assistant. And/or later integrate into Home Assistant.