by DrkAngel » Sun Jul 10, 2011 10:32 am
Testing Recycled Li-ion Cells!
Testing cells is the most laborious part of building your HomeMade Li-ion, or Lipo, battery pack!
It is important to test thoroughly.
A few extra hours testing, before assembly might give you years of trouble free use.
Start with an excess quantity of identical packs!
Ideally you should begin with with enough cells to create 3 packs.
I would recommend 2600mah cells.
2600mah cells were produced after the contaminated cell recalls, of previous years.
(Metal particulate contamination produced possible internal shorting, during certain productions.)
Smaller capacity cells will be older, but price and availability, might make them a better option.
(If worried about recalls of an older battery pack, investigate notebook battery recall, by manufacturer and model. Before purchasing batteries.)
Most laptop packs have cells paired, or connected, leave them connected, it makes final assembly much easier.
Step 1
Charge a batch of cells to an identical voltage, I recommend 4.2v, make sure your volt meter measures 1/100ths.
Preliminary charging, then ganging cells together into parallel banks, for final top-off charge, is recommended.
After attaining full charge, separate all cells.
The typical charger will charge to slightly higher than 4.2v, this surface charge will equalize to actual voltage after a couple minutes.
Step 2
Allow cells to set a full 24 hours, then compare the voltage of all cells.
The percentage of voltage drop, is a good indicator of battery condition and capacity.
Mark all cells, -1 if drop is .01v, -2 if .02v etc.
Separate cells into categories, then recheck after another 24 hours.
The more days you test, the better determination of quality!
Step 3
Occasionally one cell of a pair will be bad, holding a surface charge.
So it is important to test for this.
This is done by either applying a timed power drain, then comparing voltage drop, or by monitoring the voltage sag while applying a power drain.
A larger comparative voltage drop will indicate a bad cell.
Most important is that you find cells of comparable condition.
Ideally you should begin with with enough cells to create 3 packs.
Use your best cells for one pack, the next best for your reserve or second pack the remainder might either be bad or of lesser quality.
Quantity of "good" cells will vary by brand, ah capacity, etc.
The better matched the cells in a pack are, the more even will be a charge, from a non-balancing charger.
My last pack assembly has been re-charged a dozen plus cycles and is still equalized within a couple 1/100ths of a volt.
Monitor cell voltages before, during and after recharging, especially during your 1st uses.
If anything seem "out of balance" monitor charging carefully, until problem is determined.
I do recommend the occasional balance charge, so install a balance connector, or manually equalize cell voltages occasionally.
. Anyway, where did you get that 4S balancer, and how much did it cost?
