Ghetto balance charging my out-of-balanced 36v 18650 pack!!

[nukezero]

So I asked the question if I could use a 1s1p 18650 wallcharger to balance charge my 36v 10s4p which went out of balance after 2 years. I bought this battery 2 years ago with very little knowledge of building batteries back then so that's why I bought it. Anyhow, this battery pack would only charge up to 39.8V everytime and the BMS would shut down the charger.

I measured each cell group and this is what I got:

3.748V
3.751V
3.75V
3.691V
3.751V
3.751V
3.466V
3.451V
3.459V
3.5V

So the solution was I had a cheap chinese 18650 4.2V output wallcharger. I hooked it up to the BMS balance cable to charge it at 600mA because that's the maximum output. Now it's probably going to take a while because each parallel cell is 4P. This is a 10S4P. So 2600mah x 4 = 10,000mAH @ 600mAH . Hey, at least it's safe.

I had high faith with the signalabs BMS because I have another 48v 18650-25R samsung running it for 1 year and over 200 cycles with no issues. It charges to 54.1V each time.

 

[Hillhater]

If you are going to open up a pack and mess with individual cell groups, get the right tools for the job.
A multi purpose, RC charger that can have voltage , charge , and time limits adjusted and alarms set,....will cost less than $30.

 

[nukezero]

If you are going to open up a pack and mess with individual cell groups, get the right tools for the job.
A multi purpose, RC charger that can have voltage , charge , and time limits adjusted and alarms set,....will cost less than $30.

Updated! I have found out it is due to unbalanced cells that went out of balanced.

 

[sonnetg]

I have similar issue with my home made Samsung 25R 18650 pack. 1P would not simply would not stay in balance. I probably have a bad cell in there somewhere. I use iCharger 1010 to charge the pack. I am keeping a close eye on it, but do plan to tear it down and replace the bad cell. Who would've thought 18650 cells can be defective. You might want to invest in a CellLog 8M. Makes monitoring much easier.

Your pack seems to be terribly out of balance. How many cycles have this pack seen in 2 years?

 

[nukezero]

I have similar issue with my home made Samsung 25R 18650 pack. 1P would not simply would not stay in balance. I probably have a bad cell in there somewhere. I use iCharger 1010 to charge the pack. I am keeping a close eye on it, but do plan to tear it down and replace the bad cell. Who would've thought 18650 cells can be defective. You might want to invest in a CellLog 8M. Makes monitoring much easier.

Your pack seems to be terribly out of balance. How many cycles have this pack seen in 2 years?

I was able to restore this 36V and rebalance it properly. I have cycled it three times using a 200-watt 120v light bulb. Drained it completely and recharged again to 41.9V (good enough). Then measured all cells to be within 0.01V tolerance of each other. So I was able to revive the pack. This 36V pack is my fiance's battery and she rarely rides her bike so it only saw less than 75 cycles in the two years I had it.

I guess my issue was I did not charge it and top it off as often as I should, which leads to the cell draining. This is caused probably by the way the optoresistors are putting a load on the batteries. So I guess it's actually better to charge up batteries atleast once a month, top it off, and let the BMS balance it.

I do admit, it took a LONG time to use a 600mA wallcharger to balance a 1S4P (10Ah) pack. It took almost a day to charge it and bring it up to the matching voltage.

I do love the idea of your cellLog8M. I need to buy that!

 

[dogman dan]

Other than it takes a long time, nothing wrong with how you did that. It is handy though, to have a low watt RC charger around for single cell charging, if for nothing else, the display gives you some info about how soon you might be done.

 

[MrDude_1]

If you are going to open up a pack and mess with individual cell groups, get the right tools for the job.
A multi purpose, RC charger that can have voltage , charge , and time limits adjusted and alarms set,....will cost less than $30.

even the best icharger will not get you perfect when they're out like this.... the problem with multi-cell chargers is they charge through the main battery ports and read/discharge through the balance leads.. so once one cell gets high, they sink a load through the balance leads and lower the amperage.. then the next cell gets close and it lowers some more while switching between cells with discharge load... but eventually enough cells are close that the amperage gets very low.

So it says its done. even if 1 cell is way low...

doing it cell by cell, through the balance leads is very slow, however it will get each cell up to the exact same voltage. then if you keep them balanced before they go too far out again, a multi cell RC charger, or advanced BMS will work.

but once they go that far out, its always better to go cell by cell... it just takes longer.