Lithium Ion cell Charger
Some time ago, a couple of 4.2 Volt Lithium Ion cells were donated. They were
for some sort of PDA, and unfortunately we didn't have a charger (or PDA for
that matter, also had to scrounge for a connector). We also seem to regularly
come across laptop batteries with 6 or more of these Lithium Ion cells. It seems
to be the case, that when one of these dies, there is no fix. The simplest thing
to do is just find the dead cell, and replace it (even doing this involves some
tricky soldering work), which is considerably cheaper than buying a brand new
battery pack. We've designed a board to specifically recharge Lithium Ion cells.
When the charge cycle first starts, the regulator gets a bit hot, so a heatsink on it is necessary. Below is a cell out of a Palm and one out of a laptop, which has a length of 65mm, somewhat longer and fatter than a standard AA NiCD. Also a standard PP3 for size comparison.
Built and tested charging board is available for £19 per unit.
We've now taken apart 6 laptop Lithium-Ion Batteries, and they all seem to use cells of 3.6V, even though cells can be bought with basically any voltage you care to name (Is there no standard for these things ?).Standard charge method is Constant Voltage at 4.2 Volts (This figure is still being investigated for its accuracy), followed by a constant current period. Below is a charge cycle, actual readings, (Five and a half hours) using a cell out of a laptop and the above board.
