Copied from Optimal Charge Voltage
DrkAngel wrote: ↑
Nov 30 2019 9:10am
EVE ICR18650/26V looks to have greatest energy density between 15% and 60% (approximately from 3.5V to 3.7V)
I will likely parallel enough 36V batteries to limit controller draw to <1C and limit charge dependent on anticipated need.
1 advantage is the ability to "timer" charge at full Amps, dependent on battery voltage to obtain fastest charge, without the annoying trickle charge incumbent with CC\CV charges.
Set 36V .5C "charger" to 41V but limit with timer to add the required number of Ah.
As a "reserve", there is substantial energy density down to 33V.
Older LiCo cells were near empty at 3.6-3.7V, this provided a reasonably narrow power band of 42V-37V full to empty for a 12% differential.
Newer LiCo like the Samsung ICR18650-22p "emptied" near 3.4V for a ~20% differential.
Even worse, the EVE ICR18650-26V cells I just ordered near "empty" at 3.3V for a ~22% differential.
This "differential" is the difference between performance from a full battery and a near empty battery.
As displayed a 42-33V differential has a drastic speed-torque-power variance.
Then I noticed a very dense region of energy in these EVE cells. A very large percentage resided between about 3.5V and 3.7V, more than from 3.7V to 4.2V.
How best to take advantage ... ?
Well 37V to 35V is a nice tight differential ~`5.4%. But 37V is fairly pitiful on an eBike used to 42V!
So, decided to build a battery and add 1s to the 10s BMSed battery packs.
Current plan is for 4x 10s2p +1s10p for an effective 11s8p, with larger added 1s as safety, being without BMS support. (4.5 packs = 10lb - $112.50)
This will give me (11x 3.72V) 41V "full" and (11x 3.5V) 38.5V "empty". Now that is a performance differential that I can live with.
Compare to above
This would give me near 10Ah for daily use, with a nice safety buffer towards empty and a massive additional 11Ah if I decide to "fully charge" to 46.2V for some long trip?. ( I built and charge with "MeanWell Mega-mod" S-150-48 modded with dual meter and dual external pots for 29-54V, 0-5A adjust ability)
The 15-60% cycle, within the best energy rich voltages, and the large pack ensuring low C - rate should provide a very long life with stable performance throughout each cycle! (near the voltage stability of LiFe)