Mosaic
Well-Known Member
Hi, I did some research at Battery University as I want to develop a PIC (12F675) based charger for a protected mode 10440 AAA 3.6V, 350mA Li ion cell.
Can anyone verify or comment on the accuracy of the following statements for me please?
1) Charging a Li ion to around 4.1V peak is safe but will give around 80% energy with a much greater charge cycle lifespan.
2) A protected mode Li ion will not accept over voltage or over discharge or over current.
3) A protected mode Li ion still requires a smart charger and not a dumb continuous charger.
4) Charging with a 3.7V to 4.1V hysterisis (on/off) range is satisfactory from the safety and longevity standpoint, but may not delver more than 80% - 85% of full charge.
Conclusion:
I can use a basic Nokia cell phone charger (5V, 350- 800mA) with a PIC pwm drive to a Logic FET driver via an RC filter. Two ADCs sampling across a 2 ohm precision resistor will inform on and permit s'ware control of both the charge current and the charge voltage. The logic FET will be limited to a linear mode, max current of about 200mA which is equivalent to .57 C charge rate. Resistor dissipation = .2x.2x2 = .08W = 80mW.
Maximum estimated dumb Charger V = 6Vdc at 200mA. With .4V across the current sense resistor = 5.6V remaining. With a 3V cell to be charged, that drops 2.6V at 200mA across the FET or .52W of heat to dissipate at peak load. It may be prudent to slowly ramp the charge current up from 35mA (.1C) to manage FET heating. At 35mA, FET heating is a moderate .14 Watt assuming 7VDC from the dumb charger at that low load.
This setup should permit s'ware control over the charge rate states. eg.
State 1) Trickle charge at .1C for a battery under 3V until it achieves 3V.
State 2) 200mA charge until Battery Pd is 4.1V.
State 3) Hysteresis charging from 3.7V thru 4.1V once the charger remains connected.
State 4) No charge if charger is not connected.
Can anyone verify or comment on the accuracy of the following statements for me please?
1) Charging a Li ion to around 4.1V peak is safe but will give around 80% energy with a much greater charge cycle lifespan.
2) A protected mode Li ion will not accept over voltage or over discharge or over current.
3) A protected mode Li ion still requires a smart charger and not a dumb continuous charger.
4) Charging with a 3.7V to 4.1V hysterisis (on/off) range is satisfactory from the safety and longevity standpoint, but may not delver more than 80% - 85% of full charge.
Conclusion:
I can use a basic Nokia cell phone charger (5V, 350- 800mA) with a PIC pwm drive to a Logic FET driver via an RC filter. Two ADCs sampling across a 2 ohm precision resistor will inform on and permit s'ware control of both the charge current and the charge voltage. The logic FET will be limited to a linear mode, max current of about 200mA which is equivalent to .57 C charge rate. Resistor dissipation = .2x.2x2 = .08W = 80mW.
Maximum estimated dumb Charger V = 6Vdc at 200mA. With .4V across the current sense resistor = 5.6V remaining. With a 3V cell to be charged, that drops 2.6V at 200mA across the FET or .52W of heat to dissipate at peak load. It may be prudent to slowly ramp the charge current up from 35mA (.1C) to manage FET heating. At 35mA, FET heating is a moderate .14 Watt assuming 7VDC from the dumb charger at that low load.
This setup should permit s'ware control over the charge rate states. eg.
State 1) Trickle charge at .1C for a battery under 3V until it achieves 3V.
State 2) 200mA charge until Battery Pd is 4.1V.
State 3) Hysteresis charging from 3.7V thru 4.1V once the charger remains connected.
State 4) No charge if charger is not connected.
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