Top balancing question

[fatjay]

I am getting conflicting information regarding 3.65v.

One source says after you reach 3.65v and the amperage drops to 0a, to not leave the cells at that SOC for more than a few hours as it can harm the batteries.

Another source says after you reach 3.65v and the amperage drops to 0a, to keep going for at least another 8 hours to get the stragglers, and that will slowly bring all the cells to a more precise SOC.

I'm not trying to start a fight, since i've read more than a few different opinions on the matter. But I'd like to hear people's opinions, and logic behind them.

 

[AntronX]

Another source says after you reach 3.65v and the amperage drops to 0a, to keep going for at least another 8 hours to get the stragglers, and that will slowly bring all the cells to a more precise SOC.

That makes sense if you have sealed battery with inaccessible BMS where you can't set lower balancing trigger voltages. No need to torture your cells, just set it to start balancing at 3.45V and let it absorb for as long as needed to keep all cells balanced.

 

[rodrick]

Once you have zero amp draw at 3.65 there are no stragglers your good

 

[fatjay]

That makes sense if you have sealed battery with inaccessible BMS where you can't set lower balancing trigger voltages. No need to torture your cells, just set it to start balancing at 3.45V and let it absorb for as long as needed to keep all cells balanced.

3.45v?

 

[Rednecktek]

I calculate for 3.6 and let it sit overnight. At 3.65 when the first cell hits, the charging stops regardless of what the other cells may need.

3.6 for me leaves enough overhead on the highest cell to keep the charging circuit on without cutting power to the stragglers.

 

[fatjay]

I calculate for 3.6 and let it sit overnight. At 3.65 when the first cell hits, the charging stops regardless of what the other cells may need.

3.6 for me leaves enough overhead on the highest cell to keep the charging circuit on without cutting power to the stragglers.

I think you're referring to series charging. This is parallel charging, the initial top balancing of packs before assembly. All the cells are in parallel, so if one cell hits 3.65v, voltage will continue along hte string to allow others to hit.

 

[Koyaanisqatsi]

There isn't really any way to "not let the cells sit at a high voltage". You have to build the pack after balancing without causing any discharge on them, or your balancing act was all for not. And once the current drops to zero, it's zero. So no further charging is possible. Balance until charged and then build the pack. If you're worried about keeping the cells at high voltage too long, work quickly and put some load on the whole pack once you are to a point where it's possible. Pretty much all you can do without risking putting the cells out of balance again.

 

[Rednecktek]

I think you're referring to series charging. This is parallel charging, the initial top balancing of packs before assembly. All the cells are in parallel, so if one cell hits 3.65v, voltage will continue along hte string to allow others to hit.

Good call, my bad.