Building Li-Ion battery pack

[SamTexas]

Many people on this board will tell you that Lithium-Manganese (aka spinel) will self balance when charged in series. My real life experience says otherwise. I deliberately created an unbalanced 3s1p pack (3.7V, 3.8V and 3.9V) and bulk charged them overnight using a 12.6V charger (4.2 * 3 = 12.6). This was what I got in the morning: 4.08V, 4.18V and 4.34V. No, no fire, no explosion.

1)Now wait few weeks or/and do few charge discharge cycles (80%DOD) and report results.
2)Do the same with other chemistry, report results.
3)Then learn and make conclusions on your "real life experience"

Those cells balancing works little different way.
Read this tread again for more understanding. :wink:
http://endless-sphere.com/forums/viewtopic.php?f=14&t=27702&start=15
specially LFP and flathill posts
EDIT

So you have actually have succeeded in re-balancing an imbalanced pack (3.7, 3.8, 3.9) in a few weeks? Correct? If so, you don't mind sharing the details, do you? How many cycles did you do? How many weeks? What are the cell voltages after each cycle?

 

[parabellum]

I have about 2KW on pack made with those cells, and right now siting in the office watching my bike in the window containing 900W (799.2W actually) on konions. They are not perfectly balanced with difference of ~0.03V. I think it depends on every cell individuality or maybe because I charge to ~4.1V/cell . They just stay this way for ever, my LiPos go out of balance over 1 or 2 dozens of cycles (depending on depth and riding aggression) or/and if sitting for months as well. I also overcharged 1 cell to 4.25V and trow in to the box with other individual cells charged to 4.2V exactly, after less then 1 month I could not find this cell, all where 4.16-4.18V.
I also initially charged my 24s pack with 1 cell at 0.5V higher, because 1 of my medics where reading wrong. I noticed that after 10 cycles where I identified wrong medic but the pack was in balance already.
Hope this helps.
Edit

 

[SamTexas]

Hmm... Interesting. So I have presented my actual test which proved the self balancing did not work. Then you asked me to try something else that should work, but you yourself have never done it.

 

[parabellum]

If you name 2 cases of overcharged cells getting in balance with others or packs staying in ballance "never done" then sorry, just take it your way.
To accomplish something right, you need to learn follow instructions of the whole process, not just doing first step and crying around mising right end result.

 

[SamTexas]

I also overcharged 1 cell to 4.25V and trow in to the box with other individual cells charged to 4.2V exactly, after less then 1 month I could not find this cell, all where 4.16-4.18V.

How many cells are there in the above pack?

I also initially charged my 24s pack with 1 cell at 0.5V higher...

How many cell are there in this pack? What were the voltages of the other cells?

 

[parabellum]

I also overcharged 1 cell to 4.25V and trow in to the box with other individual cells charged to 4.2V exactly, after less then 1 month I could not find this cell, all where 4.16-4.18V.

How many cells are there in the above pack?
This is just a box with loose cells I use for flashlight, to rebuild drill pack or laptop pack and any others power source (ex. I built rechargeable pack for my diving light, originally powered with D cells),.

I also initially charged my 24s pack with 1 cell at 0.5V higher...

How many cell are there in this pack? What were the voltages of the other cells?

Sorry, did little error in post above now gone trough numbers again (bad memory ) and results this pack is 24s6p so consequently 1.5Ax6sx24x3.7=799.2W. Have used 700W out of this few times.
I bulk charge to ~98.64 or~4.11v per cell with my RC LiPo optimized charger, to easy balance my other lipo pack (24s4p20A) with battery medic discharge function(it is adjustable in 0.1V steps or 4.1V in my case). In above accident 1 group (last on positive end) was showing .05V lower as I installed the battery on the bike (but it was perfectly balanced just before pack assembly). So I charged this cell group (using balance wires I have for monitoring purposes) missing 0.05V and after ~ 10 cycles I noticed that 1 of my medics is off by 0.05V but pack was balanced already. Since then it just stays in balance even with 90%DOD.
Sorry for offtopik but it can result useful info for OP. Hopefully.