Fenix TK75 problem

I recently bought a Fenix TK75. You can't have too many flashlights. I ran it on Turbo for approx 10 minutes. It got pretty hot which wasn't surprising. The next time I went to use it, it would only run on medium and highh1. When I got home and took the batteries out it has a burnt electronic smell. Also 2 of the batteries were completely discharged and two were about half discharged. I am using brand new Orbtronic 3400mah batteries. Any ideas as to what is going on with this light?

Theirs a possibility that the internal resistance of the batteries are different, I would try a different set if you can. The protection circuit of the battery that caused the smell. If it turns out to be light, Fenix has a decent warranty last I checked

Were they all charged together? All starting out at the same state of charge?

I can't see how that flashlight could discharge cells at different rates. I suspect the cells were either not properly charged to the same level, or you've got a couple of dud cells.

Or maybe 4 dud/fake cells, and they just have wildly different capacities. Assuming you started with 4 fully charged cells (which you always have to do when changing the batteries), 10 minutes doesn't sound long enough to discharge them. They sound like fakes. Other possibility is your charger is broken, and not fully charging.

WalkIntoTheLight said:

I can't see how that flashlight could discharge cells at different rates. I suspect the cells were either not properly charged to the same level, or you've got a couple of dud cells.

Or maybe 4 dud/fake cells, and they just have wildly different capacities. Assuming you started with 4 fully charged cells (which you always have to do when changing the batteries), 10 minutes doesn't sound long enough to discharge them. They sound like fakes. Other possibility is your charger is broken, and not fully charging.

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In high power multi cell lights it's important to match them as closely as possible, try and buy them from the same batch, charge them and check them all a day later to see if they behave the same. If they were from different batches in the factory the internal resistance can be different. Electricity takes the path of least resistance, so it'll drive the lowest resistance into the ground and hardly touch the others. Charging them up on different days so they go in at uneven voltages can cause problems too. Faulty batteries is the most likely scenario but not the only way this can be caused

The cells are brand new Orbtronic 3400 mah. They were originally charged with a Nitecore I2. It only charges 2 cells at a time. There is the possibility that 2 of the cells didn't get charged before they went in the flashlight. I recently bought an XTAR Dragon VR4 Plus charger. The cells were recharged with this charger. I just ran the light on turbo for 15 minutes. The 4 cells went from 4.16-4.17 volts down to 3.71-3.72 volts. Is it normal for the cells to have a burnt electronic smell after they are discharged this rapidly? This is the first high power light that I have owned.

The cells are brand new Orbtronic 3400 mah. They were originally charged with a Nitecore I2. It only charges 2 cells at a time. There is the possibility that 2 of the cells didn't get charged before they went in the flashlight. I recently bought an XTAR Dragon VR4 Plus charger. The cells were recharged with this charger. I just ran the light on turbo for 15 minutes. The 4 cells went from 4.16-4.17 volts down to 3.71-3.72 volts. Is it normal for the cells to have a burnt electronic smell after they are discharged this rapidly? This is the first high power light that I have owned.

tempestdriver said:

The cells are brand new Orbtronic 3400 mah. They were originally charged with a Nitecore I2. It only charges 2 cells at a time. There is the possibility that 2 of the cells didn't get charged before they went in the flashlight. I recently bought an XTAR Dragon VR4 Plus charger. The cells were recharged with this charger. I just ran the light on turbo for 15 minutes. The 4 cells went from 4.16-4.17 volts down to 3.71-3.72 volts. Is it normal for the cells to have a burnt electronic smell after they are discharged this rapidly? This is the first high power light that I have owned.

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Okay, so it sounds like you didn't charge 2 of the cells before using them. That would certainly explain why they were discharged flat. (BTW, never do that! It's a good thing you were using protected cells.) As for the smell, it's normal for batteries to smell a bit when they are run hot. If you're smelling something really unusual, it's possible that they vented, though I think that's unlikely especially considering they are protected from over-current (I think). You're probably just smelling the wrap cooking a bit. The smell should get less after you use the light/batteries for awhile.

Also, check your springs. I got an extender for my TK75 which normally i use as a interchangeable battery pack. I noticed that the springs on the interchangeable battery pack become compressed and no longer make a good contact with the batteries especially when the light is used on the high mode for an extended time. This light will run with only two batteries, so it usually winds up draining the set of batteries that the springs didn't lose their compress-ability and not the batteries that don't make contact. I can generally extend the springs with pliers, but they do it again when the light is used on high. This annoys me considering its my most expensive light.

tempestdriver said:

The cells are brand new Orbtronic 3400 mah. They were originally charged with a Nitecore I2. It only charges 2 cells at a time. There is the possibility that 2 of the cells didn't get charged before they went in the flashlight. I recently bought an XTAR Dragon VR4 Plus charger. The cells were recharged with this charger. I just ran the light on turbo for 15 minutes. The 4 cells went from 4.16-4.17 volts down to 3.71-3.72 volts. Is it normal for the cells to have a burnt electronic smell after they are discharged this rapidly? This is the first high power light that I have owned.

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Hmm... Not sure I would personally continue to use any cells that had been though something where "burning" occurred because of uneven discharging to the point where you smelled it.

Aren't there protections on a light like the TK75 that would prevent this if the cells are of uneven charge with varying voltages? Can somebody chime in? That's a little scary.

martinaee said:

Hmm... Not sure I would personally continue to use any cells that had been though something where "burning" occurred because of uneven discharging to the point where you smelled it.

Aren't there protections on a light like the TK75 that would prevent this if the cells are of uneven charge with varying voltages? Can somebody chime in? That's a little scary.

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To my knowledge no, multi cell lights of any chemistry, nimh, nicad, lithium primary or rechargeable, do not handle uneven charges on batteries well. Lithium batteries are more scary because they can explode. Protection circuits on the batteries help but you should always check the voltage on batteries for a high output light.