BMS balancing voltage

[burningwings]

Is it a good idea to set the balancing voltage of the BMS at 4.1 volts ? Will this allow the max charge to be 4.1 volts , thereby charging the cells to 90% and extending battery life.New Panasonic 18650pf cells 18s12p 66.6 volts. Or go for multi chargers the hobby guys use ? Thanks ES source of all knowledge !

 

[Nobuo]

The charge is actually managed by the charger, so you need to set the stop charge at 73.8V (4.1V per cell) and then also configure the charger do the "constant voltage" phase at 73.8V while BMS configured to do the balancing at 4.1V cell discharge higher cells while balancing.

in that way you get the 90% of the capacity.

If you only cut the charge by the BMS as soon you reach 73.8V you will get actually ~85% of the capacity if you are charging around 0.3C rate, because no cv "filling" phase will be done.

If you are charging at ~0.3C rate or more, if you cut the charge just when you reach 75.6V (4.2V per cell), before the cv charger phase hit, you will get in that moment close to 90% of the overall capacity.

 

[burningwings]

Thanks again ! You are the MAN !

 

[dnmun]

the balancing voltage is set by the BMS. if you do not fully charge the pack up to the balancing voltage then it will be able to go outa balance more readily. the final voltage that you charge to does not determine cycle life. cycle life is determined by the length of time the pack is left at full charge. so your pack will not balance if you do not charge to full voltage.

 

[dmwahl]

cycle life is determined by the length of time the pack is left at full charge.

Source?

 

[okashira]

the balancing voltage is set by the BMS. if you do not fully charge the pack up to the balancing voltage then it will be able to go outa balance more readily. the final voltage that you charge to does not determine cycle life. cycle life is determined by the length of time the pack is left at full charge. so your pack will not balance if you do not charge to full voltage.

Very far from the truth (length of time at full charge statement)
cell life (better term then cycle life) is a function of many things, time spent at "full charge" is a small variable of many.

 

[dnmun]

no, you are totally wrong on this. you can watch the lecture on the tesla user's website given by that professor who has his grad student as head of battery research for tesla now.

mitchji had pulled it down here once and i tried and tried to get people to watch it but nobody did so these theories about cycle life which have no basis in good science have continued. if people would just listen to that lecture there would not be all of these misinforming statements about final voltage and depth of charge and discharge with respect to cycle life.

in that lecture he explains why the legacy research on cycle life is explained by his demonstrations of the change in capacity each cycle that he was able to measure with his micro ammeters during charge and discharge to prove how effective some additives are and how the cycle life is dependent on the rate of growth of the contaminated clogging layer of the SEI.

if you have not watched it yet then you should before making more comments without fundamental research to support it as he did. if you watched it and do not understand that cycle life is dependent on the length of time and temperature at full charge, then watch it again.

 

[okashira]

no, you are totally wrong on this. you can watch the lecture on the tesla user's website given by that professor who has his grad student as head of battery research for tesla now.

mitchji had pulled it down here once and i tried and tried to get people to watch it but nobody did so these theories about cycle life which have no basis in good science have continued. if people would just listen to that lecture there would not be all of these misinforming statements about final voltage and depth of charge and discharge with respect to cycle life.

in that lecture he explains why the legacy research on cycle life is explained by his demonstrations of the change in capacity each cycle that he was able to measure with his micro ammeters during charge and discharge to prove how effective some additives are and how the cycle life is dependent on the rate of growth of the contaminated clogging layer of the SEI.

if you have not watched it yet then you should before making more comments without fundamental research to support it as he did. if you watched it and do not understand that cycle life is dependent on the length of time and temperature at full charge, then watch it again.

I have watched it, more then once, as well as read some of his published papers, and you are the one who is (painfully) misinformed.
In fact, it has nothing to do with % max charge, % DOD is what is important if you're talking about cycle life.
The only thing that's true that is somewhat close to what you have asserted is that cell degradation rate is higher at higher states of charge. But cycle life is not affected by the % max charge you use.