Very slow charge of a Li-Ion battery can be a problem?

Discussion in 'General Electronics Chat' started by esm., Jul 22, 2012.

  1. esm.

    Thread Starter Member

    Jan 20, 2012
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    0
    Hi.

    I have some PCBs that have a Lithium battery each, charged by a dedicated IC with a programmable current from 100 to 200mA, through a resistor RPROG.
    The batteries are 3.7V of 3000 to 5000mAh. 4.2V floating voltage

    Somebody know if is NOT recommended to make a very slow charge to these kind of batteries? Could that reduce their useful life-time?
    The dedicated charger IC restarts the charge when the voltage of the Li-ion voltage goes 5% below the floating voltage (VFLOAT = 4,2V)
     
  2. #12

    Expert

    Nov 30, 2010
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    Fast charging is usually the problem. The battery overheats. For the low end, I'd say don't go below 4% per day. That's 5 milliamps on the 3000 mah battery.
     
  3. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    Actually, 4% would be about 120 mA for a 3000 mA-hr battery.

    I agree there is no problem in slow charging as long as you don't overcharge.
     
  4. #12

    Expert

    Nov 30, 2010
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    3000 maH X 4% = 120 maH
    120 maH /24 hours = 5 ma

    What I'm getting at is the minimum charge current should be at least the self discharge rate of the battery.
     
  5. JMac3108

    Active Member

    Aug 16, 2010
    349
    66
    A typical Lithium Ion battery charger IC does not float charge indefinitely. Normally they have a timeout that eventually stops charging completely. Charging restarts when the battery voltage is reduced to some lower level like 90 or 95% of the 4.2V.
     
  6. #12

    Expert

    Nov 30, 2010
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    Did someone ask about a TYPICAL anything?
    I thought this was about the lowest safe limit.
    Musta missed something.
     
    Last edited: Jul 23, 2012
  7. JMac3108

    Active Member

    Aug 16, 2010
    349
    66
    #12, I did not say "typical charging method", I said "typical charger IC".

    I was responding to comments by both you and bounty hunter that seemed to be concerned about low levels of charge over a long period of time. You said "the minimum charge current should be at least the self discharge rate of the battery" and Bountyhunter said "agree there is no problem in slow charging as long as you don't overcharge".

    My point was simply that if the OP was using a typical LiIon charger IC then he does not need to worry about overcharging (re: Bountyhunters comment) or maintaining the battery above self-discharge levels (re: your comments). I should have been more explicit about what I was saying. Sorry for any confusion.
     
  8. #12

    Expert

    Nov 30, 2010
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    Duly noted and corrected in previous post.
     
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