I have problems with any "standard" DOD (Depth Of Discharge) for Lithium cells.
1st "empty", IMO, should be held as the point before the discharge curve "falls off the cliff" ... when discharged at minimal discharge rate.
As should be obvious to all, differing technologies indicate differing optimal discharge points at minimal, nearly static, discharge rates.
- Capacity-0.2A.jpg (134.25 KiB) Viewed 4270 times
This collection displays 3 distinct static voltages at optimal.
3.60V
3.40V
and
3.20V
2nd This "optimal" DOD point shifts-drops a variable amount, dependent on discharge rate!
EG With laptop cells of a static cliff point of ~3.60V
At .2C discharge cliff point is ~3.60V
At .5C discharge cliff point is ~3.50V
At 1C discharge cliff point is ~3.30V
At 2C discharge cliff point is ~3.10V
RC Lipo packs sag similarly relative to their discharge capabilities, might sag to 3.10V but, at a 10C discharge rate.
Capacity Mapping helps determine optimal capacity ... charge discharge voltages.
Rather than running an actual discharge test, this "map" was built by carefully measuring the manufacturers discharge chart.
(
Compare to discharge test for same Sanyo cell)
(
Oops! 3.50V line should be labeled 3.55V ... 3.50V would touch and ~fill empty space )
This, hopefully" illustrates the minimal residual-available capacity after the "cliff point" highlighted in most discharge graphs.
Best way to determine your maximum DOD?
1st - Determine your optimal minimum voltage EG 3.60V
2nd - With battery near this voltage, run eBike at "normal" for a moderate time and monitor actual battery voltage.
Note and mark this typical use voltage as your "in use DOD".
Be aware that lighter or heavier use can vary this DOD voltage drastically
Alternately
With battery near your determined cliff point, run at various throttle for moderate periods (but not long enough to drain battery below cliff point).
Release throttle for a few seconds and note recovered voltage, should be slightly below static cliff point.
Compare at various throttle use and get a feel for when quick throttle check indicates optimal DOD.
Note and use as your quick check maximum DOD = empty indicator.
Oh ... I recommend a mounted volt meter to monitor battery!
With my 7s, I can combine a 8 wire ethernet cable to 1-8s VMA (Volt Meter Alarm) to monitor cell level voltages at the bars, or Cell-Log etc.