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Capacity test (after 6 months)

  • firethorn Thursday, November 7, 2013 3:39 AM Reply
    The following is a capacity measurement for these cells.

    All cells charged (~1A) individually and then discharged (1A) individually with the imax b6 charger. Discharge cutoff at 3V.

    Note: These cells were ordered about 6 months ago (~Feb 2013). They arrived in the usual dx timeframe. I am only testing them now because I just got the imax b6. Also, I had no need for these cells until now, so they are unused.

    1560mAh
    1569mAh
    1622mAh
    1658mAh
    1691mAh
    1702mAh

    If you read those numbers sequentially, the grouping seems to be very good. But.... From both extremes, the difference in capacities is about 150mAh. This isn't great but isn't too bad.

    If the capacities were higher, I would be very happy with this grouping.

    I am using these cells to build a 11.1V pack. Although I budgeted for all cells to be 1500mAh, I was really hoping that they would hold at least about 1800mAh.

    Compared to the "true 2400mAh" sku.20392 cells, the trophy for value seems to go to the sku.20392 cells. *Don't take it to mean that the sku.20392 cells are great though.

    **This thread seems to sum up the comparison in the last paragraph: http://club.dx.com/forums/forums.dx/threadid.960290
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  • sheepish Top 10 Forum Poster Thursday, November 7, 2013 4:24 AM Reply
    Very interesting. Thanks. That's not great capacity for "2500mAh" cells, or for any 18650 cells, really. I should probably retest my sku.20392 cells (which I charge with a very cheap charger).

    http://club.dx.com/forums/forums.dx/threadid.960290
    Remembering 30 years.
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  • firethorn Thursday, November 7, 2013 5:43 AM Reply
    np.

    That's not great capacity for "2500mAh" cells, or for any 18650 cells, really.

    Indeed. With just these and the sku.20392s, it averages 1800mAh. I may have to remove these from the pack.

    Hopefully the other cells I have to test will be better. sku.19624 sku.5776 sku.6979

    I had close to 2000mAh with one of the sku.6979 cells but I'm not calling it yet because it may not have been fully charged. The cool looking button apparently meant that at least 2 of those cells were not fully charged. So this 2000mAh one may actually hold more.

    *crosses fingers.
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  • desolder Top 10 Forum Poster Thursday, November 7, 2013 11:49 AM Reply
    Thanks for the test results, firethorn.

    For a 3S2P pack, you can maximize the overall capacity by paralleling the worst cell (1560mAh) with the best (1702mAh), and the 2nd worse (1569) with the 2nd best (1691). This way all three 2P groups will have as similar a total capacity as possible, which will minimize the capacity imbalance and maximize the useable capacity.
    What's up with the scrubbed LED driver IC markings?
    What are they trying to hide?

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  • firethorn Saturday, November 9, 2013 6:05 AM Reply
    That's actually brilliant desolder. Why didn't I think of that!

    Of course, just to reiterate what you said, all cells at the same point in each "pack" will need to be paralleled. One can't just join the "+" and "-" of each pack.

    Luckily, it's all paralleled for me! Thanks!
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