Messed up top balancing - how to proceed?

[beckkl]

I just assembled a Seplos case with 16 EVE cells that have been sitting on my office floor for over a year. I did top balance them a few months ago, or at least I thought I did. Once I assembled the pack the BMS is reporting cell voltages ranging from 3.356 to 3.475. There appears to only be a 3 or so cells that were on the lower end. I verified the readings were correct with my multimeter.

Any thoughts on how to proceed? I was thinking of just charging up the few cells individually (I'm assuming I'd have to somewhat disassemble the pack), but wanted to make sure this was actually necessary? I have not charged or discharged the battery yet.

 

[nc73]

put them all in parallel and charge it with a power supply or use a bms with a balancer

 

[timselectric]

Charge it, and see where they are actually at.

 

[time2roll]

If the Seplos does not have an active balancer.... add one. Then it is a matter of limiting the charge voltage until the voltages settle out.

 

[beckkl]

Charge it, and see where they are actually at.

Kind of what I was thinking. I can't think of any reason not to try first. Really don't want to rip apart the pack to top balance them again.

 

[beckkl]

If the Seplos does not have an active balancer.... add one. Then it is a matter of limiting the charge voltage until the voltages settle out.

Any recommendations on one besides the seplos one?

 

[timselectric]

Kind of what I was thinking. I can't think of any reason not to try first. Really don't want to rip apart the pack to top balance them again.

You don't have to take it apart.
You can charge the individual cells, while they are connected together. (As long as the battery isn't connected to anything else)
But charge it first, to see what you are working with.

 

[time2roll]

Any recommendations on one besides the seplos one?

If I was spending money it would be a NEEY. However I have not used this item.
I have a couple Heltec that work fine even if a bit slow.

 

[beckkl]

You don't have to take it apart.
You can charge the individual cells, while they are connected together. (As long as the battery isn't connected to anything else)
But charge it first, to see what you are working with.

So, dumb question. There isn't a good place to attach my bench charger leads to individual cells without removing the bus bars. How do people normally charge an individual cell in an already assembled pack?

 

[timselectric]

So, dumb question. There isn't a good place to attach my bench charger leads to individual cells without removing the bus bars. How do people normally charge an individual cell in an already assembled pack?

Connect to the bus bars, that are attached to the cell you want to charge or discharge.

 

[beckkl]

Connect to the bus bars, that are attached to the cell you want to charge or discharge.

Lol, duh. Long week

 

[beckkl]

Well, I charged the cells to within 10mv variance. 3.399 - 3.408 (as read by the seplos BMS). Charged the pack to 56.8V, ended with a 60mv variance. Not sure if that is bad or not. I assume if I took it all the way to 57.6 it would have a bigger variance.

 

[timselectric]

60 mv isn't bad at all, for the first full charge.
Hopefully your BMS can balance the rest of the way.

 

[houseofancients]

Kind of what I was thinking. I can't think of any reason not to try first. Really don't want to rip apart the pack to top balance them again.

If need be, let you seplos stay at a charge voltage of 3.48 for about 48 - 72 hours
That will allow the internal passive balancer to work it magic.

Also, make sure you do charge to 3.5v minimum once in a few days, again the passive balancer needs a bit higher voltage to be able to do its thing