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Testing a 18650

Discussion in 'Batteries and Chargers' started by KurtVD, Oct 14, 2018.

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  1. KurtVD

    KurtVD Super Member ECF Veteran

    Jul 2, 2018
    Switzerland
    4806F05C-B408-4B2F-AF95-DB42841058DA.jpeg I have 6 18650 cells from a notebook battery pack that I think should still be ok (the BMS of these packs had the reputation of going bad long before the cells). I have charged them individually and used them a little, but how can I find out what C rating they have? Also, how do I determine their capacity (mAh)? Drain them to a low voltage (how low?) and see how much I can charge them?

    P.S. I do not intend to use them in my mods, but this is the only forum where I’m already subscribed and where I might get this information.
     
  2. Hawise

    Hawise Ultra Member ECF Veteran

    Mar 25, 2013
    AB, Canada
    Drain to 2.5 v and charge to get the mAh rating.

    To find the C rating, discharge the battery at gradually increasing rates until it overheats and sustains damage. That's when you'll know what the C rating isn't. Just as a side note, I believe it costs around $10,000 to get the equipment you'll need to test it properly.;)
     
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  3. KurtVD

    KurtVD Super Member ECF Veteran

    Jul 2, 2018
    Switzerland
    Isn’t 2.5 V too low? If I’m not mistaken, the under volt protection of most boards is set at 3 Volts, isn’t it?
     
  4. Baditude

    Baditude ECF Guru ECF Veteran

    Apr 8, 2012
    Ridgeway, Ohio
    I don't believe you can find the C rating of a battery without sustaining enough damage to it that it is no longer usable. This is how battery manufacturers come up with the C rating and amp specification "maximum continuous discharge rating" by abusing the battery to the point of battery failure.

    If these batteries came from a battery pack, are there still weld marks on the ends of the batteries?
     
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  5. Baditude

    Baditude ECF Guru ECF Veteran

    Apr 8, 2012
    Ridgeway, Ohio
    Yes, discharging a battery below 2.5 volts will likely "kill" the battery. I think that was my point about abusing a battery to find the C rating and maximum continuous discharge rating. That is how manufacturers come up with the safety standards of the C rating and CDR.
     
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  6. Topwater Elvis

    Topwater Elvis Vaping Master ECF Veteran

    Dec 26, 2012
    Texas
    From my data sheets it is a nominal 2400mah 1C cell / 2.4a

    Their cycle performance test was 80% of initial capacity at 300 cycles using .7a discharge.

    Not something I'd reuse at all, recycle.
     
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  7. DaveP

    DaveP PV Master & Musician ECF Veteran

    Supporting member
    May 22, 2010
    Central GA

    I'd buy a charger that reads the internal resistance of the cells when charging. I use a Zanflare C4 4 bay charger. Internal resistance is a good indicator of battery condition. Most of my new cells read in the 20 to 25 milliohm range. As they age and deteriorate the IR will rise to 200 to 300 milliohm range. When that happens it's time to recycle it.

    Looking at MAH is also a good indicator. You will only see the MAH value for the amount of charge you restored to the cell. Most new cells are rated at charging from the 2.5v level, so charging from 3.x won't give you the full rating. It's a good indicator, though. Internal resistance readings tell you much more about the general condition of the cell. Lower is better.

    Think of MAH like a fuel tank. If it's empty it takes lots of gas to fill it. If you still have a quarter of a tank, not nearly as much is required to fill it up.
     
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  8. Topwater Elvis

    Topwater Elvis Vaping Master ECF Veteran

    Dec 26, 2012
    Texas
    Not all 18650 cells have the same depth of discharge capabilities.

    The data sheet for this cell also shows a discharge cutoff of 3.0V.
    Internal impedance of 55 mΩ. Depending application 110mΩ could be considered end of useful life.

    These are not particularly good or even decent cells when new, no real reason to 'test' them for another use, recycle.
     
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  9. KurtVD

    KurtVD Super Member ECF Veteran

    Jul 2, 2018
    Switzerland
    Thanks a lot for all of your answers!
     
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  10. DaveP

    DaveP PV Master & Musician ECF Veteran

    Supporting member
    May 22, 2010
    Central GA
    I"m finding that to be true. My Hohm Life 26650's read 4320 MAH charging from 3.3v (rated MAH). My 18650's, even new ones, read much less than rated MAH when charged from 3.3v. The published spec varies according to the rating scheme.
     
  11. KurtVD

    KurtVD Super Member ECF Veteran

    Jul 2, 2018
    Switzerland
    Sorry, I haven’t seen your question before, but the answer is yes, although some of them came off clean, most of them are still on. Why?
     
  12. Baditude

    Baditude ECF Guru ECF Veteran

    Apr 8, 2012
    Ridgeway, Ohio
    Because those weld marks create physical distotions that can negatively affect electrical conductivity and the cells ability to make contact with whatever tool you may have anticipated using them in.
     
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  13. KurtVD

    KurtVD Super Member ECF Veteran

    Jul 2, 2018
    Switzerland
    True, that was going to be a problem, good thinking! (Not anymore, since I’m not going to use them at all). Removing them is probably not that difficult, but it has to be done swiftly, I guess, if you don’t wanna damage the cell with the welding iron...
     
  14. Rossum

    Rossum Surly Curmudgeon Verified Member ECF Veteran

    Supporting member
    Dec 14, 2013
    SW VA
    I suspect you are confusing the terms "welding" and "soldering".
     
  15. KurtVD

    KurtVD Super Member ECF Veteran

    Jul 2, 2018
    Switzerland
    Yes, thanks! (I wasn’t sure, but I was too lazy to look it up, English isn’t my first language)
     
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