I would like to build a charger to charge two Lithium-Ion battery packs which are rated at 12V/9800mAh. They were bought on ebay and the provided mains chargers are useless - they say 12V/300mA, but I can only get 140mA out of them. After discharging one battery pack to 10.31V (and peculiarly the onboard circuitry did not switch the battery off as I had expected - I wonder how low will it let the voltage drop to?), the mains charger failed to charge the battery over 11.5V.
I have now charged one battery pack using my bench PSU at 12.6V and 1A in a couple of hours.
I would like to build my own charger to be able to charge these battery packs. My initial approach would be to use an LM317 to provide exactly 12.8V. Use a constant current sink transistor to set the current to something like 800mA max. Connect the battery in-between.
Then I would like some indication of charge status and auto-switch off (so I can power it on and go). For that I was thinking of using a reed (or other 1A relay) with an op-amp to compare against some reference voltage.
I attach a simple schematic as a start. Please let me know what you think.
I have now charged one battery pack using my bench PSU at 12.6V and 1A in a couple of hours.
I would like to build my own charger to be able to charge these battery packs. My initial approach would be to use an LM317 to provide exactly 12.8V. Use a constant current sink transistor to set the current to something like 800mA max. Connect the battery in-between.
Then I would like some indication of charge status and auto-switch off (so I can power it on and go). For that I was thinking of using a reed (or other 1A relay) with an op-amp to compare against some reference voltage.
I attach a simple schematic as a start. Please let me know what you think.
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