15 June 2013

Da b0mb :)

This battery pack worries me, and I created it!

You are looking at a 4S(1P) Li-ion battery and charging electronics assembled out of parts from an hp/Compaq battery pack.

Five wires run from cells to the charger, which are used for charge balance. Since cells were already partially charged I had to be very careful not to short wires together. Next time I will solder first on the PCB side and then to the cells!

Charging at 1C (> 2 Amps) heats up cells. At one point the charging electronics was drawing 250mA into a couple of SMD transistors, which got pretty warm. I have no idea why that happened, because re-applying the power restored the charging process.

Once again charge was stopped at 4.0x V per cell, with a light unbalance. The bq2060 chip reports 80% charge, but that's probably computed from its past "experience" with other cells.

Next step will be to evaluate residual capacity, both of this 4S1P pack and the refurbished 4S2P. I don't have a costant current load so I will stick to a 12V car lamp and stop discharge at 3.2V/cell.