Charge a li-ion battery with consumption

Discussion in 'The Projects Forum' started by sosoro, Jul 29, 2013.

  1. sosoro

    Thread Starter New Member

    Jul 28, 2013
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    How can I charge a battery that has attached a variable power consumption?
     
  2. wayneh

    Expert

    Sep 9, 2010
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    If your charger power supply can handle the combined load of the battery charge current plus the device, it's not a problem. Do you have a charge controller that is appropriate for your battery?
     
  3. sosoro

    Thread Starter New Member

    Jul 28, 2013
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    I have a charger for my battery, but the output is only 350mA, and the consumption is 4-700 mA.. So I need a charger that outputs 1000 mA?

    And if the consumption is variable, the battery can be charged? Because I know that in the charging stage the current must be stable and in other stage the voltage must be stable..
     
  4. Ramussons

    Active Member

    May 3, 2013
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    To put in simply, If your charger has only One output, for your application, the charging current will vary, as will the voltage.

    Ramesh
     
  5. wayneh

    Expert

    Sep 9, 2010
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    Yes, if you want to charge at full rate while also operating under full load. You could get away with 750mA and accept slow/no charging at higher load. But even then, it's not wise to run any appliance at its rating.
     
  6. Ramussons

    Active Member

    May 3, 2013
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    What is the capacity of your battery? in Ampere Hours (AH or mAH).

    To avoid charging the battery at a rate above its maximum recommended, you will have to ensure that the max current the charger can supply is limited to "Max charge rate + min load".

    As your load varies, the charging current of the battery will vary, but a lower charging current will not cause any damage.

    Also ensure that the max output voltage of your charger does not exceed the max permitted charge voltage of the battery or the max permitted load voltage, whichever is lower.

    Ramesh
     
  7. wayneh

    Expert

    Sep 9, 2010
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    Yes, my answers presumed that there was a smart charger involved in the process, not just a power supply. Ramussons' warnings are important. It's not easy to charge Li-ion safely without a smart charger.
     
  8. sosoro

    Thread Starter New Member

    Jul 28, 2013
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    My battery: 6.3 Wh

    A smart charged is involved, but this was my question, If I have an consumption attached, how the smart charger will know when the battery is charged?

    Let say that I know this info:
    - smart charger for the current battery: 4.2V/350mA
    - minimum consumption of attached device: 400mA
    - maxim consumption of attached device: 800mA
    I will need a smart charger with the output of max 4.2v/750mA


    How/in how many hours the battery will be charged if I have a medium consumption of 600mA (will remain 150 mA for battery)?
     
  9. Ramussons

    Active Member

    May 3, 2013
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    As a thumb rule, your battery can be charged at 630 mA (6.3 AH /10 H).
    You need a charger that can supply 4.2 V (Battery Voltage) @ 630 + 400 = 1030 mA, say 1 Amp.
    At a nominal load of 600 mA, your battery will get a fully charged (from a totally discharged condition) in about 16 hours (6300 / 400 = 15.75).

    Ramesh
     
    Last edited: Aug 1, 2013
  10. wayneh

    Expert

    Sep 9, 2010
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    Is it really quoted in W•hr and not A•hr or mA•hr ?

    If the nominal voltage is ~4V, then your battery is 1.6A•hr and will need 10 hours or more to charge at 150mA.
     
  11. Ramussons

    Active Member

    May 3, 2013
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    Yes, you have a point there. In which case, my suggestions go totally haywire :mad:

    Ramesh
     
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