Help identifying salvaged cells?- Mtbr.com
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  1. #1
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    Help identifying salvaged cells?

    Short story, sister in law's dell laptop quit powering up unless it was on AC power. I ordered her a replacement battery and all was well with the laptop.

    I opened up the OEM Dell pack to see if I could scrounge a couple of cells that may not have pooped the bed, when to my surprise all 6 cells in the pack show 3.84v or better. 2 of them are even showing 4.1ish. I guess the circuit board in the pack itself had crapped out.

    The dell pack said it was an 11.1v, 56watt/hour pack. Am I correct in the math that this works out to be 2500mah cells?

    Does anyone have a reference to try and determine what brand these cells are? I would think dell sources decent cells for their OEM packs. The wrapping is red, and the only text on the cells yields no Google hits for me:

    MKPM4C6. This on all 6 cells
    Then there is a numeric: 0634xx where the last 2 digits are randomly different.

    I don't have a charger yet that I could use to test capacity, any other way I could test the health of these cells?

    Sent from my cm_tenderloin using Tapatalk 2

  2. #2
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    Looks about right to me. (Wh / V x 1000 = mAh) so = 5045mah. It's 3s2p. So divide by 2 = 2522mah cells. They are almost certainly 2600mah cells, most likely Sanyo (from the red colour). Obviously they are unprotected without the board.

    Should be good cells. See how they perform. Get yourself a cheap hobby charger, turnigy accucell 6 or something similar. Pretty inexpensive. Or charge up and put in a light or whatever you have that uses 18650's and measure voltage at different times etc. Dont discharge below about 3v.

  3. #3
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    Testing voltage with no load is deceptive. My experience with savaging cells from 2 packs had me first thinking I had all good cells. Put a load on them and in each case there was a pair that dropped voltage quickly.

  4. #4
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    I've tested ~60 or so cells from duff laptop batteries and of those, about 10 or 12 were worth keeping. My routine:
    1) test voltage of parallel pairs, anything <1V or that looks suspicious is chucked
    2) charge all the cells up, ideally in parallel pairs to save time. Leave them somewhere safe for a week. Come back and measure voltage. Anything <4.1V gets chucked.
    3) discharge all the cells on my hobby charger (Thunder AC or something), chuck or find a home for anything <1.8Ah, which is almost all of the rest. I've had some cells that have held 4.2V for weeks that turn out to only have 300mAh of capacity left.

    Still better than them going straight to recycling though and the ones that are left are useful in all kinds of things.

  5. #5
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    Quote Originally Posted by Vancbiker View Post
    Testing voltage with no load is deceptive. My experience with savaging cells from 2 packs had me first thinking I had all good cells. Put a load on them and in each case there was a pair that dropped voltage quickly.
    Thanks for the tip.
    i went and load tested the cells a bit.




    Quote Originally Posted by mattthemuppet View Post
    I've tested ~60 or so cells from duff laptop batteries and of those, about 10 or 12 were worth keeping. My routine:
    1) test voltage of parallel pairs, anything <1V or that looks suspicious is chucked
    2) charge all the cells up, ideally in parallel pairs to save time. Leave them somewhere safe for a week. Come back and measure voltage. Anything <4.1V gets chucked.
    3) discharge all the cells on my hobby charger (Thunder AC or something), chuck or find a home for anything <1.8Ah, which is almost all of the rest. I've had some cells that have held 4.2V for weeks that turn out to only have 300mAh of capacity left.

    Still better than them going straight to recycling though and the ones that are left are useful in all kinds of things.
    Matt,
    I can't follow your method exactly, since I don't have a charger that can tell me what it is taking out or putting in yet.

    I did charge all cells individually. Looks like my charger cuts off a cell at 4v, which sucks, but oh well. I'll get a Turnigy or similar soon.

    I have a 18650 battery case wired for 2 cells in series. I picked 2 cells and plugged into a simple single xr-e light driven by a 1A buckpuck as a load.

    I timed discharge runs watching the voltage of the battery pack. First pair held up about 40 minutes and dropped below 6v, and started dropping out quickly under load. Under load one was down under 1volt and he other was just under 3.

    My next pair acted similarly. I set the 2 cells that dropped out quickly aside and retained the better of each pair. The 3rd pair held in well for more than an hour, drawing down evenly before they got too low. That pair had not been charged initially.

    I then grabbed the 2 that held in longer on the first tests without recharging. They gave another 30 mins or so.

    Then I pulled out my remaining name brand cells, 2 unprotected trust fire 2500s and one protected, that I had charged the other day. Of the 2 unprotected cells, one of them gave up under load after about 25minutes. I took the strong unprotected and paired with the protected, and got over an hour before the voltage dropped too low.

    So I think I've identified a couple of cells for the trash, and a few more that have some life left.

    Although, on a fresh charge a 2s 2500 mah pack should be driving this light into the 3+ hour range, which none of the pairings seem capable of.

    Sent from my cm_tenderloin using Tapatalk 2

  6. #6
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    hey, no problem, I was more outlining what I do, rather than trying to tell you what you should do.

    The full charge then self discharge test you can do with a DMM and should weed out a few duff cells. Then doing what you did (a discharge by a known load) is perfectly valid. Your [email protected] should be drawing ~0.5A from a 2S battery, so a 1Ah pack should last ~2h or a bit less, due to driver losses. Even without fully charging your cells to 4.2V (which would yield, I dunno, another 10-20% capacity?) your Trustfires should be running down after around 3h.

    Unless something weird's happening with your load, it sounds like all the pack batteries and your Trustfires are duff

  7. #7
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    Ok- got me a Turnigy AccuCel-6. course now I'm having to figure out how to use the thing. Seems like the charger and my DMM are about ~.3v off from each other. The manual for the charger is written in Engrish, but still it doesn't get into calibration.


    Oh well - my IT guy gave me a couple of other fried packs - 3 identical Dell packs. @ least they're the same on the outside. 2 of them came apart no problem, Sanyo is molded into the inside of the plastic case, apparently that's who made the whole pack assembly. A lot of these cells are way under 3V and I'm guessing are all pretty tired. I've discarded several that the Turnigy won't even initialize.

    The 3rd case was glued where the others were snap-together. Once I cut it open, I find 6 grey cells where the other 2 sanyo packs were red. These cells are identified as LG cells, and 4 of them are holding ~3.9v. 2 of them are completely dead - won't measure at all on the DMM. I trash those 2, and discharge each of the remaining @ 1A on the Turnigy. then I recharge @ 2A (I'm guessing ~1c), and all 4 take in the neighborhood of 1800-1900mah. I might have actually found a couple of keepers here.

    Seems like the failed batteries in the pack were the problem there, vs. the overused batteries in the sanyo packs.

  8. #8
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    Thanks for this thread. Otally forgot I have an old laptop that caved. The battery was to blame but i will follow the methods here and see if any are good.

    Turns out 2 cells(1 pair) were 0v. Some are under 3 v. Not sure if thats a bad thing
    Last edited by machine4321; 10-08-2012 at 08:50 PM.

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