Re: [EVDL] Phd in Materials Science on LiFePO4 batteries video WAS: Lithium 60ah 144v
tomw <[email protected]> wrote:
> =93You really should set your charge point higher than that. 3.4v is not a
> sufficient average to actually charge lithium cells. At that point you
> easily have a most every cell never get to the knee and thus you have no
> real idea what is going on with them. They end up in a virtually
> unmeasurable limbo.=94
> JRP3 states in the same post that he bottom balances his cells, so he kno=
> what their voltages are at the low end of the discharge curve. He knows
> cell voltages differ at the top, so he doesn=92t charge them high enough =
> the highest voltage cell to get over-charged.
Yes, they won't be overcharged, that's for sure. I just think 3.4v is a
little low since it will not reliably get most cells past the knee. I
suppose it's not necessary to get past the knee so long as your charger is
set to charge for the proper amount of time.
> =93Charging a lithium cell (LiFePO4) with 3.4V is like charging a 12v lead
> acid battery with 12v. There is a reason that people tend to charge to at
> least an average of 3.6v per cell.=94 What is that reason, and why is th=
> Volt only charged to 80% SOC if cells must be charged above the knee each
> charge cycle?
80% is where the knee is. So they are charging until it hits the knee and
then stopping. That would be about 3.5-3.55v
> What bms are you using that datalogs cell voltage and other parameters?
> Mine does not datalog.
Well, I'm using an Elithion BMS but I datalog from it with a dash mounted
display that I wrote firmware for (www.kk-ev.com). So, in all fair
disclosure I suppose I have a limited financial interest in BMS since I
write firmware for a datalogging display. But, believe me I don't get rich
doing that; my primary interest in BMS is because I think it's useful and I
use one personally.
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