Fenix TK61 teardown and mod thread

Yupp. As seen in OP.. More like 4,7x amps to be precise with one R030.

Pretty impressive huh.. Not so useless info to know about afterall. Although, that does not mean its not dangerous for the driver. :p I just means it went fine when I did it. :D Its worth to mention again that I did it without any thermal pads or heat sinking done to the driver. So with thermal pad + normal outdoor use you are probably much safer.

(btw, both tests were indoors. First were around 15-20 minutes or so. I did not time it.. Turned off the light when it felt "hot enough".)

I know some details about the transistor/MOSFETs mods that vinh is doing.

Ill let RMM continue with his MOSFET testing, and let him do the talking. Technically its beyond me...

Thanks for the great answer :slight_smile:

I understand that every part is different, and that even on stock can be burned, that’s why are electronics, but still you get very good results.

BTW, assuming on stock TK75 gets to 2850lm, (Fenix is spot on with ANSI) with this mod, 3.0A >4.6/4.7A, the 4400 lumens should be led lumens, and OTF should be around 4300? or driver efficiency comes into play additionally compared to stock?

Its probably around 4500 LED lumen at that current.

Differences in LED Lumen and OTF are the losses you get in reflector, lens, and possible things that blocks light (Bezel, locating ring and such). I don't know exactly, but I would probably expect at least 10-15% lower OTF numbers. Fenix does have very good design, reflectors and AR lenses. So maybe its as high as 4000 lumen OTF?... oh well. Lets try to keep to TK61 in this thread. :)

Hmm 4000 is a bit on a low side, because Fenix get like 950 lumens per led on stock (it was measured)

The loses from lens/reflector should be the same going from ~ 2850 >4000+ lumens or even if a bit more, still it should be around 150 lumens per led loses compared to ~ 80lm at stock and this is big downgrade i estimate, it should be less.

It should be around 4200 imho…knowing that at 4.7 the leds should output around 1500 lumen x3 = 4500 - 200 we are around 4300/4200 at worst imho (with loses/efficiency)

Sorry for offtopic!

If you say stock emitter current is 3A that means about 1120 lumen at emitter based on graph above. I dont know if its 3A stock. But you said so. You said its measured at 950 OTF too right? That is about 15% lower than 1120 lumen.

Graph shows about 1500 lumen at 4,6A. Which means 4500 lumen. Minus 15% equals about 3825 according to the graph above. I believe that match`s numbers (graph you used) were emitter numbers? I cant remember if it was T6 or U2 bin.

You have to take into account that these numbers are just different peoples numbers. They may not always be 100% comparable, or 100% accurate. Unless you measure it with a calibrated equipment we will always be doing guesstimates. People many not even have the same emitter temperature when doing these tests, which also changes things due to heat sag. What Im saying is. Some might say 4000. Some might say 4200. Some might say lower, some might say higher. If I use Djozz charts (which I believe similated OTF but without lens), we would probably be looking at around 4400 OTF with 3x XM-L2 U2 at 4,6A.

Also, on certain Fenix light, some here at BLF measure quite similar numbers, some measures higher with well above 10%.

Whatever you actually are seeing, you wont see the difference between 4000 OTF or 4400OTF anyway. It could be just the same, just like these guesstimates we are doing based on different peoples data. If you say 4200, then Im not going to argue with you against it. Your guesstimate based on available info seems to be as good as mine. When that is said. Relic38 had a giveaway where people guessed OTF numbers on a light based on given spec. You can see how large the differences were. I averaged the closest guesses I believe. This obviously makes me king of guesstimates. :p

Oh well. Enough Off topic. Start your own thread if you want to discuss something not TK61 related. :D

(Topic? "Modded TK75 lumen guesstimates based on assumed emitter current - A non TK61 mod thread")

Mine showed about 2.85A to the emitter, stock, on my meter. I have mine up to around 5.8A but haven't had time to put it back together yet, too busy building other stuff!

Richard, just throw it in a box and send it to me, I’ll put it back together and do some, ahmmmm, testing. :slight_smile: Hey, no problem! That’s what friends are for! :wink:

3 minutes on turbo and counting...fingers crossed.

For maximum output I think the way to go is an FET driver, or four Knuckleheads running in unison.

As a point of reference, my stock light measured 1200 lumens in my sphere, the light at 5.8A with the stock emitter shows 1900.

Fair enough buddy, i will just addd that i’m not sure that the loses are proportional with current bump….imho you wont lose more lumens, if you use the same flashlight, if the loses are already 10% on stock, making the light ~ 40% brighter, wont produce additional 10% lose (but i could be wrong)

On,

WOW 1900 lumens @5.8A? thats sickkkk. I pray for your light lol :smiley:

Ok, it made it 11 minutes and is still working. Body was very hot around the driver and pill, but it survived! I fried four emitters playing with this driver, but it turns out that most of my tinkering was likely unnecessary. I played around with every MOSFET on the board, but the only one I ended up leaving changed is the "C00C" MOSFET next to Q2 (I don't recall the number itself.)

I removed the stock "C00C" MOSFET and replaced it with four piggybacked IRLML2502 MOSFETs. With only one or two it was too hot to touch in a matter of seconds, with four it will get too hot to touch within about 30 seconds, but it's a big improvement and it's holding for now.

Here's what I have stacked on top of the stock sense resistors (I kept on adding until I got to 5.8A, so you can use different values to get the same effective resistance.)

(2) 100 ohm (1 on each bank for all)
(2) 75 ohm
(2) 25 ohm

The flyback diode is also getting pretty warm, but not too hot to touch. I will run it for a while longer tonight and see if it holds up.

I still think that (4) Knucklehead drivers running at 2A each would be pretty awesome...8A at the emitter, that's what I'm talking about. Will it work? As soon as my coils come in I'm going to try some running in parallel with 1 MCU to rule them all!

Oh my oh my, thats some HARDCORE PUSHING! impressive :party:

Very nice info and thanks for sharing.

8amps would be simply incredible. I would love to see that happen! I have to think it’s possible as long as it’s really well regulated and there are Zero spikes.

I have to say I’m pretty happy with mine after adding the R025 but then again, who doesn’t want more?

RMM, what other changes did you make to the driver besides the resistors? What resistor did you add to get to 5.8A?


I should have finished reading the whole thread. ROFL. Don't mind me... :P

Thanks for the update RMM and all your work!

Now process my latest order and take my money! :p

My future plan is still currently HX-1175B.

I would check into your numbers btw. You measured 2,85A at the emitter and 1200 lumen OTF stock. Those numbers does not seem to go hand in hand to me. Even if the emitter saw 3A. Would you expect 1200 lumen OTF? Seems too high compared to Cree`s own data, Match, djozz, Fenix, Selfbult, etc.. For all I know, Fenix could have gotten U3 and not mentioned it, but I doubt it. Still, would seem a bit high.

It does seem a bit high to me as well, but unfortunately the stock light I was measuring was a different copy. I never measured the one I modded beforehand, so I don't know how high it really was. I have a suspicion that the current is actually a bit higher at the emitter than what my meter says, due to the extra resistance of all the alligator clips, etc. I was using.

Solder a loop in (basically extend the negative lead) and clamp around it. Piece of cake and little to no extra resistance is added. On the bench, it’s easy to measure directly from the leads between the driver and emitter, no splices cuts or clips required.

Congratulations RMM!
good job! ;)
These should be even better mosfet:
http://www.mouser.com/ds/2/200/irlml6244pbf-6474.pdf
if there is space in the torch, you could also change package mosfet ... ;)

Took this out last night. All I can say is that my sight was limited only by the environmental haze / dust, not by the level of light. I think I might like this one better with the dome left on but with the current cranked up, that way I get a bit wider beam. The BTU Shocker cranked up has a better beam (MUCH wider, very similar intensity) than this IMO, but this is much lighter and the runtime is much longer!

If these didn't hold up, that was going to be my next step: remote mount a 70N02. I have run several 10-15 minute torture tests and it's holding strong so far.

RMM i hope you will stock some mosfets for this light, it will be very good to have an option to buy them from your store, instead of endless searching on mouser site.