Why is Last Pack (14S) Connected to Shunt Always Out of Balance?

[Steve2649]

Hi,

I'm having a recurring issue with my 48v 550ah 14S (NMC) battery bank. I have a Batrium Watchmon 4 BMS with Longmons and the last cell (1st cell according to Batrium), the one that connects to the negative side of the Batrium shunt, always runs out of balance (higher voltage than other packs). Why is this?

The packs are connected together by 6 AWG copper wire and the last pack has 6 AWG wire that connects to 2/0 copper cable that goes to the Batrium shunt, then 2/0 goes into the NEG side of Sol-Ark inverter. The POS side of inverter is 2/0 which goes to the first cell in the 14S pack.

I have the inverter set to 90A charge/discharge on a 550ah 48v battery bank.

Thanks for any advice.

 

[Sanwizard]

Hi,

I'm having a recurring issue with my 48v 550ah 14S (NMC) battery bank. I have a Batrium Watchmon 4 BMS with Longmons and the last cell (1st cell according to Batrium), the one that connects to the negative side of the Batrium shunt, always runs out of balance (higher voltage than other packs). Why is this?

The packs are connected together by 6 AWG copper wire and the last pack has 6 AWG wire that connects to 2/0 copper cable that goes to the Batrium shunt, then 2/0 goes into the NEG side of Sol-Ark inverter. The POS side of inverter is 2/0 which goes to the first cell in the 14S pack.

I have the inverter set to 90A charge/discharge on a 550ah 48v battery bank.

Thanks for any advice.

One word. Resistance. Check all connections.

 

[Steve2649]

I checked all connections and they are tight/secure. Any time I switch the inverter to charge, the last pack in the series always immediately charges with more volts than the rest of the packs.

 

[Sanwizard]

I checked all connections and they are tight/secure. Any time I switch the inverter to charge, the last pack in the series always immediately charges with more volts than the rest of the packs.

Check with a DVM on ohms setting. Did you move cells around to verify its always last cell, or just that cell? What BMS are you using? Perhaps a balancer may help if nothing else does. Try using bus bars instead of cables?

 

[Steve2649]

I'll check on the ohms, but it is a new pack and is always that last cell. I'm running Batrium Watchmon 4 w/Longmons. I think bus bars may be in order.