I just capacity tested my 2 year old 25.9V 25.92Ah, homemade recycled Lipo pack.DrkAngel wrote:I just capacity tested my 1 year old 25.9V 25.92Ah, homemade recycled Lipo pack.
(150+ cycles & and Winter usage)
1st step was to do a balance charge, to 29.4V (4.2V per cell), I used my new iMax B8.
Then I discharged to ~25.9V (3.7V per cell).
I rated 3.7V as optimal minimum usable voltage, based on the discharge test, graphed below.
Cell variance at max discharge was within ~2 100ths volt of 3.7V, excellent, IMO, for used cells.
(1 bank "patched" by adding 1 - 18650 cell)
(Different cell types have different discharge profiles!) So test voltages were:
4.2V - full
3.7V - empty
The pack is a 7S12P, 3.7V 2160mah per cell.
With a 25.92Ah rating.
My iMax B8 balance re-charge, metered a 20.8Ah input.
Charging rate was 3A = .125-.15C, for maximum efficiency.
Giving a 80.2% , of rated, capacity!
Acceptable for old recycled cells! ... ?
(Maximum capacity input measured 24Ah, deeper discharge, (last year))
This pack was built from the reject Lipo packs.
These recycled cells were pulled from the laptop packs that failed to recharge in the oem charger.
I still have 8kWh's of these packs that do charge properly - designated eMotorcycle "fodder".
Typically I do not charge this "fully" or discharge this deeply.
4.16V - full
3.75V - empty
are the voltages I use during "bulk" charging, and typical "lowest discharge voltage".
I, variously, use a modified Meanwell clone (1V-56V adjustable 7.3A) and a 29.4V (2A) Li-ion charger (trimmed with a blocking diode.)
(Hundreds+ cycles - Thousands of miles(~4000-5000+) & and Winter usage)
Only during this last year have I reduced peak charge voltage to 4.10V.
I try to never discharge below 3.7V per cell but delved there upon occasion.
25.9V to 28.7V (3.7V to 4.10V per cell) was 15.8Ah.
From an originally rated 25.92Ah pack this might sound horrible, but ...
1. Pack is partially "de-rated" due to reduced voltage test range.
2. This pack was built using only the defective packs ... the ones that would not charge properly
3. In the eZip pack it still outputs more than 2x the power that new, nearly twice as heavy, SLA batteries do.
(And 25.9V Li-ion is a tremendous improvement over 24V SLA!)
2011 - 24.0Ah (25.9 to 29.4V)
2012 - 20.8Ah (25.9 to 29.4V)
2013 - 15.8Ah (25.9 to 28.7V)
PS - Sometime last year 1 weaker bank was "patched" by wiring in 1 - 2600mah 18650 Li-ion cell.
Repair seems to have held up nicely.
Pack is nearing retirement, I got a goood supply! of donor packs for new builds.
15 packs per eZip rebuild.
Will restrict voltages to 4.05V peak charge and 3.75-3.80V discharge.
(This will reduce available Ah for 1st year but might increase it for 2nd year and extend usable life into 3rd, 4th maybe 5th year?)
With carefully matched, good condition cells might give me 3 - 5? years of reliable daily use.
Capacity map for these cells.