Hot batteries in Fenix TK40

[TedTheLed]

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.

 

[Glock27]

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 also got to thinking that any point of shorting might not be obvious. I'm 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 can't 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. I've had my TK40 on Turbo for ~15 hours and perhaps 10+ hours on the other levels combined. No further incidents since that first night.

I'd 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

 

[Mike89]

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.

 

[Glock27]

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

 

[jahxman]

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.

 

[Twinkle-Plank]

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

 

[funkychateau]

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.

 

[4sevens]

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.

 

[Glock27]

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

 

[4sevens]

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.

 

[funkychateau]

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.

Correct - I wasn't familiar with this actual flashlight, and didn't realize that it used series stacks in parallel. So yes, the lower-voltage stack (due to a reversed cell) will receive current from any other "correct" stacks placed in parallel. And they'll continue to draw current until all the parallel stacks move to the same voltage equilibrium.

 

[brightnorm]

Using Magic Marker I always put a big + sign on the side near the battery's positive terminal. I put two or three plusses around the circumference so no matter how I pick up the battery I'll see the plus sign.

Brightnorm

 

[VidPro]

from what i saw it uses this kinda setup

|{=====]{=====]{=====]{=====]| ~4.8v on ni-mh
|{=====]{=====]{=====]{=====]| x2

that is why it still runs when you
|{=====]{=====]{=====]{=====]| ~4.8v on ni-mh
|...............................................| x0

Notes: although it will run with a single set, the load on the batteries would be nicer with both sets.
BUT
If you do not have Matched sets, in , age, type, quality, brand, capacity, internal resistance etc, you might be better running it with only 4 batts in it, till you do. run it at a lower power or something.

any single item in it, turned the wrong way, and still fully connected gives you this
|{=====]{=====]{=====]{=====]| ~4.8v on ni-mh
|{=====]{=====][=====}{=====]| ~2.4v , 1 reverse charge cell, and ~2.4v differential causing a huge 3 cell cross charging too.

mabey this explains the 3 easier, they might have been being overcharged, while the poor single is being destroyed from reverse charge? then of course adjust the numbers and the current with different types of batteries, alkalines causing you least heating, and lithium causing the most heating and most dangerous situation in general.

as to marking stuff better , here! here! some devices and thier slightly raised markers for polarity need a big Fat black arrow on white. just so it takes less time to figure out.

i am happy someone posted this, even if you blow the light up completly :mecry: it is GREAT to get user experience leading to more info about the light and how it works, so people using it can understand, and take great care in using only fully matched sets of batteries in it.
it is a great light and a great design, if everyone knows how to Feed the sucker.
as Led Museum would say " It's Feeding Time "

as mentioned the Parelleling of the 2 Series sets is done in the Holder itself, so it is when you put it in the holder , reguardless of the flashlight , that any issues would already exist, also a light under that condition might actually RUN, so it operating does not define that the batteries are set correct or matched. that work has to be done by the user when installing into the pack.

and to further clarify, this is not a Spare battery carrier you should NEVER mix , for example lithiums and ni-mh or lithiums and alkaline, or any other mix, YES including kirklands and duracell, or anything else you can think up.
|{=====]{=====]{=====]{=====]| ~4.8v on ni-mh
|{=====]{=====]{=====]{=====]| ~6.0v on lithium
as you can see another large voltage differential that is sure to drain the lithium, while overcharging the ni-mh giving you very poor life of both :sick2:
8 batteries the same, not so hard, they sell them in 12 packs

 

[flasherByNight]

Just out of curiosity...worst case scenario and all EIGHT AA batteries exploded simultaneously. How bad we talking here?

 

[Burgess]

E-L-E


Extinction Level Event





_

 

[flasherByNight]

I always wondered how the dinosaurs went out... :ironic:

 

[Glock27]

You guys are scaring me now.......if I would have been just a little slower taking out those hot cells We wouldn't be here now!?!?
I'm going to wear out my carrier soon if I keep up the rate of cycling cells through it.......and with no further events to threaten humanity!

The cheap carriers I picked up at Radio Shack are poorly built and will not make contact with the negative ends of the cells when the cells are reversed. I'll bring some copper washers I have at work to see if I can get a hot pack to happen.

G27

 

[mdocod]

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.

Unfortunately, NIMH cells can not be charged in parallel, it doesn't work very well.

In my opinion, they should have wired the pack all series, and wired the MCE 2S2P. More than likely the same driver could have been used anyways, the pack would be easier to charge, the current flowing in many places in the circuit would be lower, reducing the effects of resistance and increasing efficiency, and the dies on the LED could have been more closely matched for the parallel sets to improve efficiency and load balance between dies.


-Eric

 

[VidPro]

Unfortunately, NIMH cells can not be charged in parallel, it doesn't work very well.

-Eric

unless you Slow charge (slow enough), or use a voltage max, or a combo of those. meaning you cant the way we usually do things (v-drop), but you can with a properly done charge type. (always gotta get that disclaimer in there)

 

[325addict]

To use any rechargeable battery like this "series-stacks-in-parallel" is ALWAYS a bad idea, due to the enormous currents these batteries WILL deliver when only a small difference in voltage between both series-stacks exists.

In my opinion, ONLY 8 batteries should be used in case you use 8 exactly the same, fresh, from the same manufacturer and the same date & lot etc. ALKALINE batteries.
When using ANY kind of rechargeables, just use 4 of them, just one stack. Problems will be largely avoided then. Of course, runtime will be compromised, for this, keep 4 spares at hand.

Problem solved

Timmo.