One cell ahead of others

[hackenstein]

If you have to turn off charging to prevent the BMS from shutting off due to over current protection, your charging voltage is too high. What is it now, Screen shot??

Not completely sure what behavior you are describing. The goal is to charge with Constant Voltage of 28.0V (3.5V per cell) until all the cells are balanced within 10mV.

Im letting it rest now and active balancing is on.

When I put 27,2 on the bank the cell is running so its hard to get that 10mV difference.

I can send u a new screenshot when charging when it has rested.

 

[hackenstein]

If you have to turn off charging to prevent the BMS from shutting off due to over current protection, your charging voltage is too high. What is it now, Screen shot??

Not completely sure what behavior you are describing. The goal is to charge with Constant Voltage of 28.0V (3.5V per cell) until all the cells are balanced within 10mV.

Check the printscreen now above. I uploaded correct one now.

 

[hackenstein]

Okay I think I got it right now. I didnt charge it with constant voltage it was constant current. Sorry. Will keep charging small steps!

 

[hackenstein]

Im doing constant voltage and with very low difference. It is only 2A in the beginning and cell nr 4 keeps running. After a while the ampere is so low it stops charging and cell nr 4 is like 70mv ahead. Should I just keep doing this?

 

[BentleyJ]

Im doing constant voltage and with very low difference. It is only 2A in the beginning and cell nr 4 keeps running. After a while the ampere is so low it stops charging and cell nr 4 is like 70mv ahead. Should I just keep doing this?

If cell #4 is 70mv ahead, give it more time at that voltage. The balancer will do its job. When it gets down to around 25mV difference go up 0.1V.

 

[hackenstein]

I have been doing this for like 30 times now. I charge with about 70w. And after 10 min it is down to 0w as the ampere lowers due to constant voltage. I then let the balancing do its work til it hits 3.40v. I cant put charge more than 100w the cell runs fast. I have charged this batterypack so many times when this nr 4 cell been above 3.40. When cell nr 4 is at 3.40 the other ones are at around 3.380.

I have let the cells rest for about 1,5 day. The runner Cell nr 4 had the lowest voltage, 3,350v, is that allright resting when charged to 3,4?

I have put the cells in parallel I cant sit and do this forever.

 

[BentleyJ]

3.35V per cell is a normal resting voltage. For example my batteries (16S) settle down to 53.6V in about 6-8hrs after termination of a charge cycle.

 

[hackenstein]

3.35V per cell is a normal resting voltage. For example my batteries (16S) settle down to 53.6V in about 6-8hrs after termination of a charge cycle.

I have top balanced now in parallel. I have let the cell rest for 13h now. Cell nr 4 is at 3,585. One other cell is at around 3,56 the rest 3,45. Is this normal? Should I put them in series now and all be good even if they are not in the same voltage?

 

[Ampster]

Yes, it is probably surface charge which will dissapate when connected to a small load. Keep an eye on those two during the next few cycles to be sure.

 

[MisterSandals]

I have top balanced now in parallel.

With the cells connected in parallel, did you charge with positive lead on one end and negative lead on the other end?
If you connected both charge leads to the same end cell, all cells will not have received same charge current and likely NOT be balance well/properly.

Can you post pics of your parallel and series connected charge setups? Maybe someone can spot something helpful.

 

[hackenstein]

With the cells connected in parallel, did you charge with positive lead on one end and negative lead on the other end?
If you connected both charge leads to the same end cell, all cells will not have received same charge current and likely NOT be balance well/properly.

Can you post pics of your parallel and series connected charge setups? Maybe someone can spot something helpful.

Hi, Yes I did exactly that. Positive on one end and negative on the other. Here is how the other batterybank is parallelcharging. Lets hope it is just surface charge on the two cells I mentioned. I will connect them in series tomorrow and test everything.

 

[hackenstein]

Hi again. I have connected everything. Cell nr 4 is again the lowest voltage during load after top balancing. And I also have one more problem now and it might be connected to it? I have two 8x280ah in parallel. I have the same bms on both. Same lenght on thick cables. When I put a load on it around 1000w there is quite a big difference between the two batteries. One is drawing a lot more. The one that draw less contains cell nr 4.

Anyone got any idea how this is possible? I will attach photos.

 

[hackenstein]

I have connected batteries to two busbars. And the inverter to the busbars. There is same lenght and size of the cables. I also tried switching and checking each cable. Same result...

 

[hackenstein]

Im doing a new thread on this.