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Thread: Hot batteries in Fenix TK40

  1. #1
    Flashaholic jahxman's Avatar
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    Default Hot batteries in Fenix TK40

    Hot Batteries! Yowch!

    So I got my TK40 today, and right away loaded it up with Energizer Ultimate Lithiums ( I dont have a recharge setup yet for AAs) and played with it for a while. Overall, I am pleased with the light.

    Then, I put it away, unscrewing the end cap 2.5 turns as the little instruction manual says to eliminate slow battery drain...Can't say I was all that happy having to do that, but ok.

    I put my hand on it about 40 minutes later and it was just about hot enough to cook something on! I immediately took out the batteries, and some of the lithium batteries swelled a bit, to the point that their outer foil/plastic jackets no longer touched at the seam.

    What is going on? Did I do something wrong? I am admittedly a bit of a newb here but I've been lurking at CPF for a while and decided to try this light out.

    Anyone have any ideas what's going on?

  2. #2
    Flashaholic* qip's Avatar
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    Default Re: Hot batteries in Fenix TK40

    ok that does worry me a bit , considering the L91 is my favorite battery that i was gonna have this puppy run on , and all the stories i read on primaries exploding and with the tk40 using 8 of them well

  3. #3
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    Default Re: Hot batteries in Fenix TK40

    What was the condition of the cells. Were they brand new or not?

  4. #4
    Flashaholic* EngrPaul's Avatar
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    Default Re: Hot batteries in Fenix TK40

    Sounds like you exchanged slow battery drain for fast battery drain.

    Sorry to hear that!

  5. #5

    Default Re: Hot batteries in Fenix TK40

    Do you have a way of measuring your L91īs? I use Eneloops in my TK40 and no issues. We need to get to the bottom of this.

  6. #6

    Default Re: Hot batteries in Fenix TK40

    And all the batteries where definitely in the correct way around???

  7. #7
    Flashaholic jahxman's Avatar
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    Mpr Re: Hot batteries in Fenix TK40

    OK - I may have jumped the gun on this.

    First of all, the batteries were all brand new, out of the same 8-pack.

    After this happened I put alkalines in, played with it with the alkalines, and then tried the unscrew end cap test and left it for an hour. No problems.

    I examined the lithiums I had in it before, and realized that they didn't swell up - they just got hot enough to shrink their plastic/foil jackets a little. And only three of them looked like this - the other 5 looked normal.

    I put the Lithiums back in, taking extra care of the polarity - I thought I had had it right the first time; I am a pretty detail oriented person and battery polarity is just basic. However when I took them out before they were very hot and I was more focused on getting them out than checking the polarity.

    SO I tested the light with the lithiums back in for a while, all seems normal (and turbo mode seems a good deal brighter with lithiums then with alkalines)

    I untwisted the end cap until the light would no longer come on, just as I had done before, and put it down for a while. It has been almost 2 hours now and the light is cool to the touch, tests fine, and when I check the batteries they are cool as well.

    So, I think this one was user error - I must have gotten the polarity wrong when I put them in first time, and maybe the light was mainly running on the four that had the right polarity.

    With 8 of these little suckers, I guess extra care needs to be taken with polarity, especially if using lithiums. Or you just have to not be a bonehead like me
    Last edited by jahxman; 06-05-2009 at 10:48 AM. Reason: fixing typos

  8. #8
    *Flashaholic* Burgess's Avatar
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    Default Re: Hot batteries in Fenix TK40


    _

  9. #9
    *Flashaholic* StarHalo's Avatar
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    Default Re: Hot batteries in Fenix TK40

    Something somewhere shorted..

  10. #10
    Flashaholic* Haz's Avatar
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    Default Re: Hot batteries in Fenix TK40

    How is the battery carrier and the contact with the interior of the light?. Any incorrect alignment?, I wonder if that is the place causing the shorting.

  11. #11
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    Default Re: Hot batteries in Fenix TK40

    Something somewhere shorted..
    That's what that sounds like to me, or incorrect battery placement. I have regular alkalines in mine. When it's off, it's off.
    Fenix TK40. Jetbeam PA40. ShiningBeam Caveman. ITP SA1 Eluma, ITP A3 EOS, KD C8 CREE XML T6, Amondotech Illuminator 3152 HID, and my two favorite under $10 lights, MXDL SA-28, SIPIK SK68.

  12. #12
    Flashaholic Glock27's Avatar
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    Default Re: Hot batteries in Fenix TK40

    I had a hot battery event in my TK40 last night also.
    I ran a set of Sanyo 2700s for a while and then changed out to a second set of Sanyos. All cells are new and were purchased for the TK40. I can't remember whether I had it on low or off, but when I went to pick it up a couple minutes after changing batteries, the tube felt warm. I immediately took out the carrier and the cells were very hot. I did not think any cells were installed incorrectly. I see no signs of a short.
    After cooling, 5 of the 8 cells accepted ~840 mAh. 3 took substantially more....~1200 mAh.
    Cells from the "event" set are in light now and have not heated up even on turbo.

    Does any of the above point to anything but goofing cell polarity on a pair?
    What could effect 3 of 8 cells?
    One thing I did notice is that one of the 4 Negative contact "fingers" was not bent to the same level as the other 3.
    Looks like a good idea to order a spare carrier. I don't think a loaded carrier would survive a 3 foot drop test.
    G27

  13. #13
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    Default Re: Hot batteries in Fenix TK40

    Has anyone done this comparison:
    8 x AA alkaline against 4xAA L91 lithium.
    6.5K diving light, 5K cool-white, 4K neutral-white, 3K warm-white, 2.7K extra warm-white

  14. #14
    Flashaholic Glock27's Avatar
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    Default Re: Hot batteries in Fenix TK40

    I've changed out several sets of cells since I had a pack get hot the other night.
    A close inspection of the carrier, tube and all contacts revealed no shorting of any kind. Therefore evidence strongly points to me having one cell in backwards.
    Could someone confirm one cell reversed in a 4s pack would cause the heat to rise?

    Fortunately, the Sanyo 2700s that got hot have given a consistent 2 hours and 20 minutes on 2 cycles of Turbo....so I don't think they're hurt.
    G27

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    Default Re: Hot batteries in Fenix TK40

    Well, today is the 8th and I am sure that those having problems with their TK40's have done the right thing and contacted the seller by now. What did they say? This problem sounds sort of dangerous, so the seller should know about it, if not the manufacturer, and maybe production/sales should stop till this is worked out.

    Bill

  16. #16
    Flashaholic Glock27's Avatar
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    Default Re: Hot batteries in Fenix TK40

    I have heard of no problems with the light....It is not the lights fault that a battery was probably inserted backwards. I have had no further events and have used my light every night this week.....depleting at least 1 set of 2700's a day...sometimes 2.
    I think the TK40 is a great light.
    G27

  17. #17
    Flashaholic jahxman's Avatar
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    Default Re: Hot batteries in Fenix TK40

    Quote Originally Posted by Bullzeyebill View Post
    contacted the seller by now. What did they say?
    I wrote fenix-store.com, where I got the light, and the response was:

    Jim,
    This may have been an isolated incident. How are the batteries oriented inside the light? There may be some confusion as the diagram in the instructions shows all cells positive side towards the front. In reality the cells should always be installed with the negative end towards the springs. Can you confirm this?

    Regards,
    Trevor


    I have been using the light daily, and same as Glock27 I have had no further heating events. It is possible that we both managed to reverse polarity on a cell, as unlikely as it seems to someone experienced with putting batteries in devices - but there are 8 of them in this one.

    I like the light a lot, I think others will as well - so, unless it happens again I think it was my own error. I continue to check the light 30 minutes after putting it away on lockout, just to be sure.

  18. #18
    Flashaholic* f22shift's Avatar
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    Default Re: Hot batteries in Fenix TK40

    they should consider making a carrier with a built in port. sell with a charger.
    like a fm style carrier.
    this can reduce user error with less loading.

  19. #19
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    Default Re: Hot batteries in Fenix TK40

    the battery install instructions that come with the tk40 are confusing - Trevor tried to correct the TK40 diagram by saying 'all batteries should be installed with negative ends towards springs..' but this can be confusing also because it could mean either the spring in the end cap, or the spring sticking out of the forward end of the battery carrier, doing either would be wrong: the 'spring' the negative battery terminals should 'face' ie. contact, are the springS INSIDE the battery carrier. duh right? well I did it wrong the first time --
    (hey they do things differently in China, right?)
    ...works fine now.

  20. #20
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    Default Re: Hot batteries in Fenix TK40

    the battery install instructions that come with the tk40 are confusing
    Don't know how much clearer the instructions could be dude. Almost sounds like you've never installed batteries before if you didn't know the springs would make contact with the negative end. Dunno man, it was pretty clear cut to me.
    Last edited by Mike89; 04-13-2009 at 11:10 PM.
    Fenix TK40. Jetbeam PA40. ShiningBeam Caveman. ITP SA1 Eluma, ITP A3 EOS, KD C8 CREE XML T6, Amondotech Illuminator 3152 HID, and my two favorite under $10 lights, MXDL SA-28, SIPIK SK68.

  21. #21
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    Default Re: Hot batteries in Fenix TK40

    the diagram wasn't confusing it was plain flat out WRONG; it pictures all 8 batteries facing in the same direction The written instructions were not, as I said, precise.
    Trevor himself said so, dude.
    But, congrats on your genius status, anyway.

  22. #22
    Flashaholic Glock27's Avatar
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    Default Re: Hot batteries in Fenix TK40

    Iím setting here looking at my TK40 battery carrier trying to comprehend what kind of cell reversal or short would cause 3 cells to complete a circuit and start dumping lots of heat.

    I also got to thinking that any point of shorting might not be obvious. Iím in the HVAC business and shorts in high voltage AC circuits leave pretty tell tail signs, but low voltage and current with DC might not show burn marks at all.

    I can find no nicks on any cell insulation. Insulation on carrier bars looks good. No suspect spots inside of tube, pill or tail cap.

    After drawing a diagram, I canít see where a circuit can be completed by having a cell reversed and light turned off. I know AC current well, but DC is a whole new ballgame to me.

    I have cycled both sets of Sanyo 2700s I got for the light multiple times since my one incident of a hot pack. Iíve had my TK40 on Turbo for ~15 hours and perhaps 10+ hours on the other levels combined. No further incidents since that first night.

    Iíd really like to understand what caused the pack to heat up that 1 time. I was in such a panic when it happened, I did not notice a reversed cell.........but that is still the most likely culprit.

    G27

  23. #23
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    Default Re: Hot batteries in Fenix TK40

    All I was saying was it was pretty simple. I didn't need to look at any instructions. Springs contacting the negative end of battery the way it should be. Dunno what was so difficult about that as it's the way it always is. This isn't rocket science knowing how to install batteries.
    Fenix TK40. Jetbeam PA40. ShiningBeam Caveman. ITP SA1 Eluma, ITP A3 EOS, KD C8 CREE XML T6, Amondotech Illuminator 3152 HID, and my two favorite under $10 lights, MXDL SA-28, SIPIK SK68.

  24. #24
    Flashaholic Glock27's Avatar
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    Default Re: Hot batteries in Fenix TK40

    Quote Originally Posted by Mike89 View Post
    All I was saying was it was pretty simple. I didn't need to look at any instructions. Springs contacting the negative end of battery the way it should be. Dunno what was so difficult about that as it's the way it always is. This isn't rocket science knowing how to install batteries.
    Nope, it is not hard to put batteries in the TK40 carrier. Butts on springs and buttons on pads. Please diagram how a reversed cell in a TK40 carrier would cause 3 of 8 cells to discharge their energy.
    G27

  25. #25
    Flashaholic jahxman's Avatar
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    Thinking Re: Hot batteries in Fenix TK40

    Quote Originally Posted by Glock27 View Post
    I’m setting here looking at my TK40 battery carrier trying to comprehend what kind of cell reversal or short would cause 3 cells to complete a circuit and start dumping lots of heat.
    I have also spent some time examining everything, trying to figure out how this could happen - and for me it was also 3 cells out of the 8 that got really hot. Also for me I didn't slow down when I was taking the hot batteries out to double check the polarity orientation, but I'm usually pretty ocd about that kind of thing when I put them in....

    I can't see any way to complete the circuit. I even tried putting the battery pack in with one cell reversed to see if I could make it happen again, but got no heating at all, and the light still worked (as I guess you would expect, with the two parallel battery circuits). I didn't have the nerve to leave the light on for long like this though. Also, for me the heating ocurred when the light was off, on lockout and in its case.
    Last edited by jahxman; 04-16-2009 at 09:43 AM. Reason: Fix typos

  26. #26
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    Default Re: Hot batteries in Fenix TK40

    I guess if you were to put the 2nd or 3rd battery in a set backwards it may cause a short. Just a theory.

  27. #27
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    Default Re: Hot batteries in Fenix TK40

    Reversing one cell in a series set will definitely make it heat up.

    For example, take 8 cells at 1.5 volts each, in series, for 8 x 1.5 = 12 volts. Now reverse one battery and the pack voltage is (7 x 1.5) - 1.5 = 9 volts.

    The light will still operate, but will probably draw more current as the regulator tries to hold LED current at a specified level despite available voltage being reduced. Additionally, this current will be flowing the "wrong" way through the reversed cell. The effect is identical to what would happen if you tried to "charge" this non-rechargeable cell at whatever current the regulator is drawing. In this case, I guess that could have been close to an amp or so.

    None of this should have happened with the tail cap loosened, though. The more likely thing is that the reversed cell got really hot during use, but the heat wasn't immediately felt through the tube. A little while later, the tube had conducted enough heat to hint at what had been going on earlier.

    So basically the reversed cell heated up just as expected for a non-rechargeable battery being force-fed an amp or so.

  28. #28

    Default Re: Hot batteries in Fenix TK40

    Quote Originally Posted by funkychateau View Post
    Reversing one cell in a series set will definitely make it heat up.

    For example, take 8 cells at 1.5 volts each, in series, for 8 x 1.5 = 12 volts. Now reverse one battery and the pack voltage is (7 x 1.5) - 1.5 = 9 volts.

    The light will still operate, but will probably draw more current as the regulator tries to hold LED current at a specified level despite available voltage being reduced. Additionally, this current will be flowing the "wrong" way through the reversed cell. The effect is identical to what would happen if you tried to "charge" this non-rechargeable cell at whatever current the regulator is drawing. In this case, I guess that could have been close to an amp or so.

    None of this should have happened with the tail cap loosened, though. The more likely thing is that the reversed cell got really hot during use, but the heat wasn't immediately felt through the tube. A little while later, the tube had conducted enough heat to hint at what had been going on earlier.

    So basically the reversed cell heated up just as expected for a non-rechargeable battery being force-fed an amp or so.
    Actually if you have ONE reversed cell among the 8 it will still heat up regardless of whether the tailcap is loose or even if the whole battery holder
    is outside of the flashlight. The difference in voltage between the parallel stacks will CHARGE the lower voltage string.

    When the pack is actually being used that one cell will eventually fully discharged to 0v and begins to "REVERSE CHARGE" then that cell will mostly likely rupture and begin to leak. Charging or reverse charging alkaline will always generate heat and ultimately cause a leak. Reverse charging
    a NiMH will cause ruptures and leaks too.

    Everyone, please please check your polarities. Spring side is always negative.
    Last edited by 4sevens; 04-17-2009 at 11:41 AM.

  29. #29
    Flashaholic Glock27's Avatar
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    Default Re: Hot batteries in Fenix TK40

    Howdy 4sevens! Do you have any spare carriers available?

    I am going to radio shack to try and buy a pair of 4 cell AA holders. I want to wire them together like the TK40 pack and then use some primaries and measure temp. and voltages with a reversed cell in various slots. Weird thing is that all eight batteries dumped energy during those few minutes, but 3 dumped much more. Just a few ~<20mAh between each (5/8 & 3/8 sets)

    My "hot pack" event occurred with new room temperature batteries that had a few cycles and a forming charge with a Maha C9000. Light was either off or on low for just a few minutes. The cells that got hot are performing exactly like my 2nd set so far.
    G27

  30. #30

    Default Re: Hot batteries in Fenix TK40

    Quote Originally Posted by Glock27 View Post
    Howdy 4sevens! Do you have any spare carriers available?

    I am going to radio shack to try and buy a pair of 4 cell AA holders. I want to wire them together like the TK40 pack and then use some primaries and measure temp. and voltages with a reversed cell in various slots. Weird thing is that all eight batteries dumped energy during those few minutes, but 3 dumped much more. Just a few ~<20mAh between each (5/8 & 3/8 sets)

    My "hot pack" event occurred with new room temperature batteries that had a few cycles and a forming charge with a Maha C9000. Light was either off or on low for just a few minutes. The cells that got hot are performing exactly like my 2nd set so far.
    G27
    No spare carriers at this point in time. I'm not sure if they'll offer it except for warranty use. Do be careful when loading these lights. Remember they
    are only 1.5v each - lots of room for stuff to go wrong.

    1) If you're using alkalines, ALWAYS use NEW cells from the SAME pack
    and the SAME brand. Do not mix between brands, or even cells with different
    remaining power. When the first cell depletes, immediately the continued use
    will cause that cell to begin to be CHARGED BACKWARDS.

    2) If you're using NiMH, use the SAME rating, SAME brand, same batch (purchased at the same time) and don't use those cells for other things. Keep them together for the life of the cells with the flashlight.

    Discharge and charge them together. Never mix different brands even if they have the same capacity. Never put cells with different charge states. You want to keep all the cells in the same condition all the time. Same thing happens when you nearly deplete the pack - the first cell that runs out (to 0v) first will damage the cell going below 0.7v or thereabouts and when it hits 0v, it immediately begins to REVERSE CHARGE. Just a friendly warning.

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