Fenix TK21 U2 user interface problems

So I had been wanting a new powerful LED flashlight for a toy and I came upon the TK21. I thought what a great compromise of size and output. I ordered one with four new tenergy 18650's and waited impatiently for about 5 days. I finally got it in the mail and tested it out that night only to find out that the turbo mode only stays there for about five to ten seconds and steps down to high. I am devistated by this problem because I was excited to have a new flashlight. I sent it back for a different one and hope that when I get the new one it will be normal. I hope this isn't a manufacturing defect. Anyone else out there experiencing problems with their's? By the way the light itself was awesome, my brightest one by far! I cannot wait for the replacement to come.

Actually mine did this with only one of my two Tenergy batteries. IF you have this problem with the new light, I would check to make sure it happens with more than one battery. Then check it with CR123's. You may find you have a battery problem not a flashlight problem.

Bill

I did try it with other batteries and it did the same thing. I tried cleaning all the contacts flashlight and batteries to no avail.

I'll be sure to be thorough with the new light too. If it does happen to be the batteries I hope rcr123a bats work. I hate the thought of using non-rechagables in that light.

Has anyone else noticed the issue the OP has brought up ?

chipdouglas said:

Has anyone else noticed the issue the OP has brought up ?

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I have a TK21 and use Tenergy Rcr123's, I haven't notice this issue.

I am about to make purchase of TK21 next week, after reading this tread I better check before I get one

My TK21 arrived today and I do not have this issue using 2 brand new CR123a's. My order of 18650's hasn't arrived yet so can't give you and info on the rechargeable front though however.

By the way... very nice light!! I'm like a kid in a candy shop with this new toy. Will be my EDC light along with an E05 from tomorrow!!

chipdouglas said:

Has anyone else noticed the issue the OP has brought up ?

Click to expand...

No problems here with two Duracell CR123A's. I suspect the OP just got a problem light.

chipdouglas said:

Has anyone else noticed the issue the OP has brought up ?

Click to expand...

Yes.

I have two TK21 lights in very limited use. The first has not shown the behavior mentioned (neither on Surefire 2xCR123A nor Redilast 2900 mah 18650). The second light shows the behavior (erratically) when using the 18650, but I did not experience it during the short time it was run on 2xCR123A. The battery in the second light was actually run previously in the first light. When I moved the battery I attempted to top it off in a Pila charger, but the charger indicated already full and no addtional charge was applied. I did not have a voltmeter handy and did not measure battery voltage.

These are all preliminary observations. I have not used the lights enough to come to conclusions of any certainty, nor have I checked and cross-checked any test cases. At the moment I have other fish to fry, and am not very concerned with this particular issue.

Could it be just that draw is too high for some cells? This is shame, since I was going to grap this light. Has OP something new to tell to those who are now in doubt?

TK21 is one of my favorite XML based tatical flashlight, it no doubt is the king of XML single cell (1x18650/17670/2xCR123) tatical, no matter when it's compare with other same class of product.



For the issue you mentioned, this is caused by an IC performance matter, Fenix was addressed the problem and trace that just a little bit of TK21 were equipped with those substandard IC's in first batch of the stock and shipped. So please don't worry, you just only need to swap a new one without the problem from the supplier that is ok, Fenix also have the excellence after sales service.

Cheers,

I sent back the light to the retailer and they deemed it 100% functional. They were nice enough to ship it back with an ultrafire 18650. That battery did the same thing as the tenergys I bought with the light. I did however go to my local sporting goods store and paid way too much for 2 surefire batteries. I have checked the light with the primaries and it has not done it with them in it. It only seems to be with the Li-ions. Kind of makes me mad because I really do not want to use primaries. Is it safe to use RCR123a's without the light, I ask because it says nothing about them in the manual. I have noticed that the light will skip modes especially when the tail switch is depressed. At half down my light with 18650 will go from turbo to high. Turning the light back on will bring it back to turbo but within five to ten seconds it downshifts. It is rather annoying. I absolutely love the light on cr123s.

Exact same problem on my TK21 U2.

With my AW 2200mAh cells it steps down almost immediately, when i fit 2 x CR123 cells instead it works fine.


I had some new 18650 Trust Fire 2400mAh cells arrive yesterday, a quick test and it seemed fine with those, so it seems as if it's more a battery problem than the torch.

Weird thing though is that when it steps down, it's as close to high mode as i can tell with my naked eye.
My limited understanding of the cell protection is it's a over/undercharge protection, i can't see that the protection board would be big enough to step down the voltage even if it was a useful function (which i can see no reason for having a cell step down it's output).

So logic would say it's the batteries as other cells work fine, but then i can't see a cell stepping down it's output that quickly for any reason.


Weird.

Thanks for info folks! I need to check this light out! If problems arise, I will first try some unprotected low internal resistance 18650 cells like Sanyo or even certain 1300mah cells used in power tools, then couple of 3.0volts LiFePO4 RCR123's. Unfortunately I have to wait till end of month.. paycheck and stuff, you know..

This problem has been addressed in the TK21/41/70 thread, it seems the light switches down to high mode when the cell voltage under load goes to 3.5-6v or below, to warn about low battery voltage.

What I don't understand though is that if you say it's the light warning of a low battery then why is it happening with fresh off the charger batteries?

Well the suggestion would be that the particular cells you are using have a very high voltage sag under load and so on turbo drop below the 3.5/6v mark quite quickly, even if with the load removed they jump back up to a normal resting voltage. The circuit mistakes that for the cell being heavily discharged and cuts down to high mode.

The circuit could still be at fault however, it may be cutting down at too high a voltage. I'm just pointing out why this is consistently happening, but never with higher voltage cell set-ups such as 2x 3v primaries.

If AW's sag, as has been reported, then should also.. well.. every 18650 cell. I hate this, since I have IMR cells, Sanyos, LG's, Samsungs and also very high internal resistance Chinese cells but not the light. IMRS should be ultimate test for sag hypothesis. One user said that light cuts down when the switch is half depressed. Sounds like the light is very sensitive to current changes.. or plain faulty. If I had light like that, I would use test leads and try how it behaves without tailcap.

I too have this problem... but i use using with a new uncharged aw 2900ma AW... after i charge it... it was ok... but just about 10 or 20 minute playing (all the modes) with the play in 2 days time... it starts to auto dim again ( too quick/early for me )... i would expect it to last longer... i do feel its like an indicator from the light that batt is low... but the thing is... after it auto dim itself to high... u can just click it once, it will be back to turbo and stays there.... until the voltage starts to go down till near 3.6v.. it will start to dim from turbo then high then normal in a few second time... u really should charge it by then....

btu i still feel... the run time is too short for it too auto dim down... i tot 2900ma 18650 should have a longer run time then 2 cr123... maybe i am wrong