Electronics > Power/Renewable Energy/EV's

Trickle charge lithium-ion battery after it is fully charged

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ejeffrey:

--- Quote from: drkntz on September 11, 2023, 01:45:20 pm ---Would you argue that undercharging (4.0V) and blipping a few mA with max cell voltage capped at 4.2V is unsafe? I figure I would follow a typical Li-ion charge cycle: precondition -> "fast" charge (0.1C, really not that fast) -> cap at 4.0V (instead of 4.2) -> current terminate at 0.01C -> blip (if necessary) to poll battery presence.

--- End quote ---

As long as you never exceed 4.2 volts at the battery terminals, it's safe.  Derating your charge termination voltage to equal the worst case diode drop, plus a margin for pulsed presence detection should be fine with two caveats:

1) You will be sacrificing a significant fraction of the battery capacity.
2) If it's possible for someone to go insert a fully charged (4.2 V) battery into the charger, you need to make sure that you are still operating safely. This may mean that your battery detection will not work.

One alternative is to measure the reverse leakage current through the protection diode.  Disconnect the charge circuit and try a pull-down resistor, see how much current flows through it.  Power diodes and especially schottky diodes will have plenty of leakage to measure.  One trap here is that the leakage is exponentially dependent on temperature, make sure it will operate in the lowest temperature someone might use it.

wraper:

--- Quote from: drkntz on September 11, 2023, 01:45:20 pm ---Would you argue that undercharging (4.0V) and blipping a few mA with max cell voltage capped at 4.2V is unsafe? I figure I would follow a typical Li-ion charge cycle: precondition -> "fast" charge (0.1C, really not that fast) -> cap at 4.0V (instead of 4.2) -> current terminate at 0.01C -> blip (if necessary) to poll battery presence.

--- End quote ---
You won't be able to detect batteries charged above certain level. And with a diode in series it means not detecting unless nearly empty.

wraper:
I would first check if there is voltage = battery with no diode. If voltage detected, do not apply any current for detection purposes. If no voltage detected, apply a short current pulse to detect batteries with a diode.

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