Battery read 13.4 volts but BMS reads 13.1

[moonlitsouls]

Any idea why this is happening?

 

[Bob B]

Since there is no current flowing ... One of the 2 devices is not accurate. Without knowing for sure if the meter is accurate, that is all we can determine.

On the BMS, the battery voltage agrees with the total voltage .... added up, they equal 13.152. Not sure if that is how the pack voltage is determined internally in the BMS.

If you can compare to another meter and determine your meter is accurate, there is a voltage calibration in the config section for the BMS.

 

[John Frum]

320 milli volts is a very big difference especially when the battery is resting.
Please cross-validate each individual cell, bms vs meter and post the results.

I notice your battery is balancing at a low voltage.
That will destroy your top balance, if it hasn't already.
You should only be balancing during charge and only above float voltage.
Are you charge sources configured for float?
If yes, what is your float voltage?

 

[boondox]

Get a voltage reference and check your meter's accuracy.

 

[Bubba1]

My guess is your meter is not accurate.

 

[A.Justice]

Both of those meters are on the cheaper end, so it's definitely possible that one or both is off, but because voltage has very little to do with state of charge, I wouldn't worry too much about it. I would be more focused on the remaining AH / WH from the BMS's internal shunt, or from an external one.

I have three different voltmeters on my battery box (BMS, Renogy shunt, and USB port) and all three show different voltages because of where they're hooked into the system and length of wiring. My BMS reads more or less directly off the battery, The USB port reads from the fuse box, and the shunt measures from close to the battery, but is affected by load. At full charge (13.75v, for me) the voltages show from ~13.3-13.8v.

It would never hurt to make sure your connections are tight as well.