Unstable voltage on balancing - Tesla pack

Hardware diyBMS
1

Hi - I have a Tesla model s battery pack 6s76p to which I’ve connected 6 X v4.5 boards using the Fellten adaptor board. When charging all is good until any balance resistor is activated, at which point the voltage starts to jump around 300mv and starts affecting neighbouring battery voltages. This causes the balance resistors to be activated for all cells - the only way to stop balancing is to set a high balance voltage.

One of the batteries is out of balance by 100mv from the other 5 - but this battery starts balancing as its voltage jumps around as well.

I’ve had my meter on the circuits and it looks like the voltages really are jumping around.

Has anyone had experience using DiyBMS with Tesla battery packs?

2

Had this problem every time i charged because of noise created by the charger.
Communication wires need to be twisted.
Try lower com speed.
In my extreme case (very long wires) i had to use shielded cable grounded to the cell negative.

3

Thanks for the reply - I’m looking at using an Analog Devices AD7280 which can monitor 6 series cells simultaneously. The example they give has 10k series resistors on the voltage inputs and 1uF capacitors across each cell. Presumably this is to filter any noise - so maybe you’re on to something.

Thanks again :+1: