dogman wrote:I'm not a huge fan of fussy fuss top balancing either. Nor do I advocate blindly trusting any bms.
What I do preach more than anything else is the following. The short version is don't hammer your battery, and it stays better balanced and may last longer.
Have enough capacity to make your usual discharge rate much less than factory spec maximums, and have reserve capacity when you need it.
Keep dod moderate, so that .1v out of balance will not cause a disaster. If conventient, make most charges a slight undercharge as well.
Balance the pack at the top if it gets more than 1.v out of balance. Ideally, charge just the low cell once it gets that far out, or discharge if just one cell is high. BMS balancing can take forever.
Monitor at cell level often enough to know what is happening, and if possible, replace cells that cause a daily imbalance.
Don't store a battery long periods with anything whatsoever drawing current. If you must store with a bms or other device drawing current, recharge at a sufficient interval for the the bms to restore balance.
Bring on the wind, anybody wants to argue against this strategy. It kinda works. Works good enough to make balancing needed a lot less, and the conservative dod makes how you do it less of an issue. BMS or not matters less too. A bms can't murder the battery if it never gets much of a chance to try it.
+1 for dogman i agree!
This i sthe aproach i've been using since the last 5 years now with the Konion and it work perfect!
This is the approach i would recomand to everyone using lithium cellas and also people that buy Konion cells.
People that ask me for konion often will calculate theyr battery size according to the total trip or energy they need and i have to remind them that discharging a pack fully is not a great solution for keeping balanced and in a good health their cells. Max of DOD whould be 80% or less
Also many will calculate the max current theyr controller can do and will calculate the battery they make by having the number of parallel cells that match this but they forget to have a margin! I recommand to have 150% more curent available form the battery at continuous discharge than what the controller can take.
Ex 1p konion 18650V cell can do 7A continuous and 15 burst until it reach 50 celsius. this mean that your controller should draw about 4.5A per cell i parallel. so if you have 50a controller, you should have about 75A max continuous discharge from your battery wich correspond to 75A / 7A = 10p cells. so for a 50A controller, i would recommand 10p of 18650V cells.
I also agree with Luke. By top balancing you use your cells in a way that you get more Wh energy per volt since you have a larger part of the dishcarge that occure at higher voltage than with bottom balancing The Ri is lower at higher voltage so the voltage sag is less so it translate that you get more Wh per volt of discharge since more Ah are at higher voltage.
I other words in top balancing, the first Ah you get is at higher voltage meaning higher Wh ( Ah x volt = Wh) than the first Ah with bottom balancing that have discharged at lower voltage due to the lower cell at the top that limit the total pack max voltage voltage.
The energy of each Ah depend on the voltage at wich it is charged or discharged.. and this is what make diference in this bottom or top balancing situation.
I wold thing you can get a little bit more energy( wh) by using top balancing than bottom balancing.