Do I need to top balance?

[timblack1]

I purchased 16 LFP cells and an Apexium battery box kit which includes a BMS from Jenny Wu. Everything seems to be in perfect condition. I am very pleased.

On my first voltage test after opening the boxes, 12 of the cells each have 3.256 volts. The other four cells vary by only one millivolt higher or lower than that. So currently they are balanced, but at a medium voltage. Their voltage is not at the top of the cells' voltage range.

The BMS includes an active balancing feature. I have not done an internal resistance or capacity test on these cells because I don't have the equipment to do so.

Should I top balance these cells before assembling and using the battery? Or, should I trust the BMS to top balance them for me while or after they charge for the first time?

 

[Partimewages]

Fully charge and top balance. It's not always necessary but saves headaches down the road.

 

[Brett V]

Measuring 3.2 volts is no indication of them being at the same SOC, you have no idea of how close they are. Some will say slap it together and let the BMS top balance them for you but if you want it right, top balance them first.

 

[time2roll]

I would skip the old school parallel top balance. Assemble as a battery with the BMS. Limit the initial charge to monitor the balance as the battery approaches full. Once voltage can easily go to 55.20+ place the battery in service. Continue to monitor the cell balance as voltage is increased to the desired level.

 

[timblack1]

I would skip the old school parallel top balance. Assemble as a battery with the BMS. Limit the initial charge to monitor the balance as the battery approaches full. Once voltage can easily go to 55.20+ place the battery in service. Continue to monitor the cell balance as voltage is increased to the desired level.

Interesting. This sounds like real top balancing, because I would still actively and personally monitor each cell's voltage. The fact that it uses the BMS's active balancing to accomplish the goal of top balancing does not obviously show me that it is anything different than real top balancing. If I test each cell voltage directly using a multimeter rather than rely on the BMS's sensors and potential small voltage drops caused by the sensor leads and connections, this sounds to me like it could be nearly identical to "old school" top balancing. Am I missing something which would be a big reason not to go this route?

 

[740GLE]

IMO an active balancer of 2a does everything an old school top balance will do (except it will save you time and limit any possible damage due to human error). So many times people try and “top balance” and then somehow a cell or two gets up to 3.8v due to flakey bench top supplies.

Active balance just saves so many beach aches and works assuming you have enough time to keep the charge voltage where cells are above 3.45-3.55v. IMO no need to bring them up to 3.65 as long as cell delta looks good.