Different sessions values in EVE + JBD BMS - same voltages in cells

[Sharkboi]

Hi there,

I'm running two 12v 280ah EVE cells with JBD 200A BMS in parallel. All seems to be working well but when I check the status of the BMS I notice a difference in the 'session values'. According to this information one battery seems so get a lot more discharge then the other one. I don't understand why as the voltages of the cells are mostly equal, with a difference of only a few thousand volts.

Where does this difference come from?

Sessions values:

	Bat 1	Bat 2
max volt	14.21v	14.21v
max chg	30.53A	20.25A
max power	2452 w	1417w
min volt	12.79v	12.84v
max dist	186.75A	107.91A

 

[sunshine_eggo]

Hi there,

I'm running two 12v 280ah EVE cells with JBD 200A BMS in parallel. All seems to be working well but when I check the status of the BMS I notice a difference in the 'session values'. According to this information one battery seems so get a lot more discharge then the other one. I don't understand why as the voltages of the cells are mostly equal, with a difference of only a few thousand volts.

Where does this difference come from?

Sessions values:

	Bat 1	Bat 2
max volt	14.21v	14.21v
max chg	30.53A	20.25A
max power	2452 w	1417w
min volt	12.79v	12.84v
max dist	186.75A	107.91A

How are your batteries connected? Picture would be best.

Are all connections properly torqued and of high quality?

 

[Sharkboi]

see picture below.

The cells are internally well connected and torqued as specced.
I mostly don't understand why the values are different while the cell voltages are the same, shouldn't they be different as well?

 

[sunshine_eggo]

Image is too cropped. It looks like you have multiple connections to the battery.



Essentially, you should only be connected to the (+) on ONE battery and to the (-) on the other.

Otherwise you are creating different paths of resistance that will cause different current to/from the individual batteries.

The cells are internally well connected and torqued as specced.
I mostly don't understand why the values are different while the cell voltages are the same, shouldn't they be different as well?

LFP cells in the operating range are expected to have very little deviation due to the flatness of the voltage curve. The two batteries in parallel must be at essentially at the same voltage and as such, the cell voltages will be essentially the same.

As you get to the extremes - high SoC and low SoC when - cell voltages change rapidly.

Your battery should look like this:



It appears you have a second connection at the positive, and I can't see if you have another connection at the negative.

 

[Sharkboi]

Hi,

many thanks for your reply, very helpful.

The batteries were connected differently from your wiring diagram. I think this may have been the issue.
I will reroute and test.