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  1. #1
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    Finding a bad cell in a battery pack

    I have a 6 cell side by side GP4300. This bad boy used to be great till I had a little accident that caused the battery to be ejected and one of the battery cells vented. I replaced that bad cell, but evidently one of my other cells is bad also. After a charge the pack doesn't have the punch it used to and only lasts about 6 minutes (used to last 15). I can't visibly tell which one it is (could be more than one?). How should I go about checking to see which cell is bad? I have a multimeter that tells me that they all have roughly the same voltage when not under load. Any ideas would be appreciated.

  2. #2
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    If you can afford one of these you can find the bad cell !!!

    http://www2.towerhobbies.com/cgi-bin...&I=LXAFW2&P=ML
    Last edited by BT_EMT; 11-18-2006 at 04:06 PM.
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  3. #3
    Traxxas Marshal cooleocool's Avatar
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    If there was a bad cell, you'd be able to notice a difference in voltage.
    "Happiness depends upon ourselves." -Aristotle

  4. #4
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    Try checking the volts and amps hot off the charger. Both the whole pack and for each cell. Also feel if any of the cells are different temperatures. Then let it sit for a few hours. Recheck the volts and amps. And resistance if your meter has it. Next run the pack till it starts to fade, and immediately recheck each cell with the meter. Check it again after it has cooled off and sat for a while. While I'm not qualified to preach electrical theory, I have a lot of experience troubleshooting electrical stuff, and that is my "hacker" way of doing it. Just try to find a difference and that is your problem cell, even if you don't understand the electrical concept. Also do the voltmeter thing on a known good pack, so you can get some reference numbers on what readings you should get from a working cell.
    If you stick with NiMH, and not Lithium, I would recommend you get a cell equalizer like the Novak Smart Tray SE, the Trinity one, the Tekin Battery Doctor etc. Then at least each cell can be reconditioned to take the same charge and hopefully peak at the same time once you find the bad cell or cells.

    http://www2.towerhobbies.com/cgi-bin...?&I=LXKYP6&P=7
    http://www2.towerhobbies.com/cgi-bin...?&I=LXMXZ7&P=7
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  5. #5
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    Edit: Looks like I missed the part of your original post that states you've already read the voltages, my bad. I would charge the pack, and measure each cell's voltage while under load, good cells should stay close to 1.2. Any cell that drops below 1.0 volts is probably bad.

    Fred
    Last edited by FP Racing; 11-18-2006 at 10:53 PM.

  6. #6
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    I tried to charge the pack today and the pack wasn't even registering on the charger. I resoldered a couple of the battery bars and all was well. I tried running the pack in the pede and it lost power all of a sudden. My soldering job must not have been too great. I'm going to resolder the whole pack. Any suggestions on how to get all of the old solder off without getting the cells too hot?

  7. #7
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    There are 2 things you could use to remove the solder, solder wick or a solder sucker. Radio Shack SHOULD have both.

  8. #8
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    What brand/wattage soldering iron are you using? Is the tip nice and clean? Are you using flux? What brand of solder do you have? Do you have a soldering jig? Don't forget to scratch the battery surface up with some sandpaper prior to the final soldering.

    This is a great article about soldering.
    http://www.xtremerc.com/pages/howto.php?howto=11&page=3

    http://www.xtremerc.com/pages/quicktips.php?page=2
    Last edited by BT_EMT; 11-19-2006 at 06:06 PM.
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  9. #9
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    I use a 40 watt Weller soldering iron. The tip probably needs replaced. I use the rosen core solder you get at Walmart. I don't normally use flux because the rosen core is supposed to be all you need. I did rough up the battery ends with a hobby knife for better cohesion. I guess I need to use flux too even though my solder has is 60/40?

  10. #10
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    Well as long as your solder is called Electrical solder it should be ok. Deans makes some good stuff. I'd use the flux, cause that's what the article said to do if for no other reason.... Back in the 80's I didn't know any better, I used regular plumbing lead solder. I also did not realize how important it was to have a clean solder head. I'm not sure about the rosen core thing. But it can't hurt to follow that "How To" lesson from XRC. Or you could go LiPo and not ever have to solder a pack again !! Maybe Santa will bring you a Max Amps 12,000mAh LiPo !
    Last edited by BT_EMT; 11-19-2006 at 09:44 PM.
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  11. #11
    Traxxas Marshal cooleocool's Avatar
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    I use Deans solder. I was going to get Novak solder because it has a 3% silver content V. Deans which has a 2%. I still haven't ran out of Deans yet though. Down to my last one...
    "Happiness depends upon ourselves." -Aristotle

  12. #12
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    Quote Originally Posted by BT_EMT@msn.com
    Well as long as your solder is called Electrical solder it should be ok. Deans makes some good stuff. I'd use the flux, cause that's what the article said to do if for no other reason.... Back in the 80's I didn't know any better, I used regular plumbing lead solder. I also did not realize how important it was to have a clean solder head. I'm not sure about the rosen core thing. But it can't hurt to follow that "How To" lesson from XRC. Or you could go LiPo and not ever have to solder a pack again !! Maybe Santa will bring you a Max Amps 12,000mAh LiPo !
    I figure by this time next year I will have all lipo's. But for now I'm going to continue to use the nimh batteries.

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