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Query related to mobile phone charging

  1. Mar 12, 2009 #1
    Hi Guys, :smile:

    My mobile phone battery was completely drained and so I put it up for charging. However, inspite of the charger providing charging current to the cell phone, the phone shut down several times indicating ‘Battery Low’.

    As per my understanding, the charger charges up the cell phone battery and also provides electrical power to the cell phone circuitry in parallel. So, I fail to understand as to why the phone shut down inspite of the charger supplying electrical power to the phone circuit ?

    Also, if the cell phone did shut down, it would mean that the drained battery was still supplying or attempting to supply electrical power to the phone’s electronic circuit inspite of the charger being perfectly connected. (this was verified as the phone display indicated that battery charging was in progress).

    So, my query is; How can the battery charge itself and at the same time manage to supply electrical power to the mobile phone circuitry ? How can a battery charge as well as discharge at the same time ? Can someone please provide me with a suitable explanation for this phenomenon as it completely goes against the laws of electrical physics! I would be very grateful.

    Thanks & Regards,
  2. jcsd
  3. Mar 12, 2009 #2


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    Batteries do not charge and discharge at the same time. Either the applied voltage is greater than the battery's own (and the battery charges), or the opposite, and the battery discharges.

    When the phone is connected to its charger and turned on, some of the current goes to operate the phone, and some of the current charges the battery.

    The phone turns off based on the battery voltage. If the battery is heavily discharged, it will have a very low voltage, even while being charged. (The battery is a much lower resistance than the charger, so the battery will drag the charger voltage down.) Thus, the phone can end up turning off due to the low battery voltage, even while being charged.

    - Warren
  4. Mar 12, 2009 #3
    :smile:Thanx Warren , very much grateful. So, from your quote shall i conclude that the phone turned off several times as a result of the terminal voltage across the phone being dropped to a very low value by the drained battery which now acts as a resistive load of a very low value across the charger ? This might then be the cause of insufficient voltage across the phone to sustain charging...... resulting in the phone to shut down. The phone might then re-boot once again as soon as the battery voltage across the phone circuitry would be sufficient enough to keep the phone all juiced up.

    Plz correct me if i am wrong!

    Kind Regards,
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