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Will an over-discharged "dead" battery be woken up by NFC wireless charging?

Luke_Lin 135 3
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  • NFC-WLC trickle pre-charge recovers cells below startup threshold

    #1 21958396
    Luke_Lin
    Level 2  
    Posts: 12
    When lithium-ion batteries are deeply discharged, even down to 0 V, many charging solutions have an undervoltage startup threshold. A battery over-discharged to 0 V can no longer be recharged with those solutions.

    However, the NFC-WLC protocol supports trickle pre-charging. Even when the battery voltage is below the system startup threshold, the harvested RF energy can supply a tiny current to safely recover the battery.

    Important note: Pre-charging parameters must be strictly tuned to prevent battery damage.
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  • #2 21958453
    LEDówki
    Level 43  
    Posts: 9678
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    This is done by the TP4056 chip, and all lithium-ion battery chargers do this. Initial charging takes place at a current of 50 mA or 100 mA until a voltage of 2.5 V is reached. Once this is reached, further charging continues at the rated current. The pre-charge current depends on the capacity of the battery (secondary cell) being charged.
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  • Deeply discharged Li-ion cells pose internal shorting hazards

    #3 21958506
    jarek_lnx
    Level 43  
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    A deeply discharged Li-ion battery becomes dangerous once recharged. Internal short circuits and fires may occur. This is why charging circuits shut down; it is not because of any technical difficulty in starting the circuit when the voltage is too low. The fact that some users have managed to charge a battery from 0V does not mean that any equipment manufacturer will accept the risk of subsequent failures.
  • #4 21958530
    LEDówki
    Level 43  
    Posts: 9678
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    Exactly – a battery like that has high internal resistance and a much lower capacity than usual. The longer it has been left completely discharged, the less likely it is that some of its capacity can be restored.
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