Best way to drain Li-ion batteries prior to recharge?

Discussion in 'General Electronics Chat' started by RogueRose, Jan 14, 2016.

  1. RogueRose

    Thread Starter Member

    Oct 10, 2014
    189
    4
    I have a lot of Li-ion 18650 batteries that I want to use for a few projects. I'm sure they are all in different states of health and charge, so I figure that draining them (to whatever safe voltage is best) and then charging them would give the best results.

    I'm also going to build a charger where I want to incorporate over-charge protection. Can the same component be used for both applications?

    If there is a fairly easy process of draining the batt's w/o killing them that doesn't involve building a circuit, I'm interested in that as well.




    On a side note - another project related to this...

    I'm also interested in building a charger where I can charge at least 4 individual cells (probably more like 8-12) and also a charger that I can charge many cells in series (cells of all the same make/model/age - so they should charge relatively similarly). I want to build in over-charging protection into this device.

    I'm considering using a standard ATX PSU as the power source for this device as I can use the 3.3 or 5v for the single cell charge source and then the 12v rail for charging 3 cells at a time (24v is even possible from this unit, although only at ~1-1.5A which is still decent).
     
  2. DC_Kid

    Distinguished Member

    Feb 25, 2008
    638
    9
    i thought Li bats didnt need a drain like the old Ni-cad's did.
    charge rate and charge full control is whats needed.
    others can correct me if i am wrong
     
    RogueRose likes this.
  3. dl324

    Distinguished Member

    Mar 30, 2015
    3,249
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    Deep discharge of most battery types will decrease lifetime. If you want to discharge batteries, you need a circuit to monitor battery voltage and remove the load when they're discharged to your specified voltage.

    You didn't mention how you plan to configure the batteries (single, series, parallel, series-parallel). Anything other than single requires matched batteries for best performance.

    Charging batteries in series or parallel is a bad idea.
     
  4. RogueRose

    Thread Starter Member

    Oct 10, 2014
    189
    4

    Anything in series/parallel will be the same model when in a pack and charging.
     
  5. dl324

    Distinguished Member

    Mar 30, 2015
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    Even for batteries of the same type, some can be weaker or stronger than others.
     
  6. crutschow

    Expert

    Mar 14, 2008
    13,024
    3,236
    There's no good reason to discharge Li-ion batteries before charging as long as you have the proper Li-ion charger for the battery you have.
    Any discharge just serves to reduce the battery's life.
     
  7. hp1729

    Well-Known Member

    Nov 23, 2015
    1,957
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    Interesting. Have you had a specific experience in mind on this. Most battery packs are in series and charged together.
     
  8. dl324

    Distinguished Member

    Mar 30, 2015
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    And the weakest battery determines end of life.
     
  9. hp1729

    Well-Known Member

    Nov 23, 2015
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    So a battery pack is no better than its weakest cell?
     
  10. dl324

    Distinguished Member

    Mar 30, 2015
    3,249
    626
    Yes.
     
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