My 29.6V 31.2A (8s12p) Sanyo 18650 cells seem to have suffered an early demise.
After barely 1000 miles, pack is deteriorating quickly.
Cells began as an 6s16p (22.2V 41.6Ah) stuffed into an eZip RMB shell.
See -22.2V Battery Woes
While initial tests provide 60 miles @16+mph and ...
"41.6Ah pack (4.20 - 3.71V per cell discharge) accepted 32.86Ah recharge, at an estimated 80-85% DOD, for a ~38-41Ah capacity!
So cells appear to be of excellent capacity condition."
... I felt performance "... inadequate".
Initially I considered converting pack to 12s8p (44.4V 20.8Ah) but decided on a more utilitarian 8s12p (29.6 31.2Ah).
After initial excellent speed and range, recharge Ah began reducing with nearly every cycle.
I blame my own ignorance!
Initially I discharged to near 3.6V and charged to 4.20V, using my mAh/100thV Discharge Capacity Map
as my guide.
Unfortunetly, of fortunetly, I developed a method of capacity mapping using charge mAh/200thV
This method precisely quantifies the amount of electricity to raise pack voltage between steps of voltage.
Results were enlightening!
It seems discharging below 3.72V is needlessly damaging!
Further, all experts agree, lowering peak charge voltage greatly increases capacity and cycle life!
A 1/10V reduction in charge voltage will double usable life!
As indicated by the graph, the last capacity bulge ends at 4.05V.
Keeping voltages between 3.72V and 4.05V should increase usable life to 300%!
This from an initial loss of usable Ah of a measured 18%.
Well, this is merely a prelude to my next project using my best Sanyo 18650 cells.
9s12p (33.3 31.2Ah) will squeeze into an eZip RMB pack.
I have 108+ saved (best bleed down) cells.
Bleed down test revised to maintained above 4.05V after 6 months - my last bulk charge of candidate cells.
But I intend on retesting all my Sanyo cells with my Bulk Capacity Test
, 60 cells at a time.
All cells will be discharged rated from 4.10V to 3.7V.
33.3V pack will work on my 36V controller Winter eZip and my universal controller eZip LS.
I intend on keeping a spare oem geared wheel-motor combo, ready for quick swap for high torque 20mph legality from 33.3V.
I have to keep my upgeared eZips for my 25.9V Lipo packs.
7s12p is the best I can squeeze into the RMB pack.
Last build gave adequate performance for 5000+ miles. (Still use it for quick trips around town - 6500+ miles)
Charge Capacity mapping indicates a 50% increase in usable life by reducing charge to 4.15V, with a miniscule loss of capacity!
Test was run twice to confirm odd capacity bulge between 4.10-4.15V.
Alternatively, reducing charge voltage below 4.05V increases usable life +300% ... but with a 25%+ loss of capacity.
25.9V 26Ah Lipo pack reduced to to ~18Ah usable ... might be worth it for 6 years of daily use - vs 2 years.
Best of all ... I can use a 2nd battery in the rack for longer trips ...