Problems charging Li-ion

Discussion in 'Homework Help' started by Zeebit, Jan 18, 2014.

  1. Zeebit

    Thread Starter Member

    Nov 8, 2013
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    0
    I have a couple of 5300mah 3.7v li-ion cells and I have a few problems charging these. I have discharged these to about 3V. I then connected them in parallel and the resting voltage is about 3.4V.

    I am charging the cells using a DC PSU. I have tried it on both an old BK precision and an Agilent. I forgot the model but the problem is the same when I use either of the two.

    I charge the two cells in parallel by setting the voltage limit to 4.2v and initially setting the current limit to 500mA. When I hook up the cells, the psu goes to CC mode as expected. However, when I increase the current limit to around 570mA the supply would switch to CV mode.

    I don't understand why this happens.

    I tried adding a 1N4001 diode in series to each cells. I then set the current limit to 1A and voltage limit to 4.9V. When I hook up the cells, the supply goes into Cc mode as expected.

    Why does this happen? With the cells alone, the supply goes to CV when the current limit is about 570mA but when I added a diode it goes up to 1A.

    The cells do not have a protection pcb.
     
  2. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,159
    Shouldn't you be charging at 0.1c?
     
  3. Zeebit

    Thread Starter Member

    Nov 8, 2013
    72
    0
    Only if cell voltage is below 3V. Once it goes above that it an be charged at 0.5C to 0.7C.
     
  4. Zeebit

    Thread Starter Member

    Nov 8, 2013
    72
    0
    Sooo...any ideas why?
     
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