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Thread: Review of Fenix TK41, with measurements and outdoor beamshots

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    HKJ's Avatar
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    Default Review of Fenix TK41, with measurements and outdoor beamshots

    Fenix TK41





    This light is the 3. light with 8 AA cells from Fenix, this time the light is using the XM-L led (The other where MC-E and 3xXP-G). The light has four brightness settings and two flashing settings, controlled with two electronic side switches. The light is made of aluminum with hard-anodized (Type 3) finish.





    The light is supplied in a plastic box with cardboard wraparound.



    The box contains the light, a lanyard, two spare o-rings, a warranty card and the manual.



    The light has a large smooth reflector with a XM-L led in the center, as can be seen in the beamshots this reflector does give the light a very good throw.



    The head has some flat surfaces that prevent the light from rolling. Around the led there is a heatsink to help radiate up to 11 watt of heat.



    Behind the heatsink is the two switches, one for on/off and selection between steady light or flashing modes, the other switch to select brightness level or flashing mode. The switches are electronic, this means that the light will have a small standby current drain.



    The head has a good quality thread with an o-ring for connect to the body. The backside of the head has the connection to the battery carrier, this is a solid construction with a circuit board that is reinforced with metal where the springs from the carrier connects.



    The body is covered with a checkered pattern and on the squares there are small ridges, this gives a good grip on the light.



    The tail has holes for the lanyard and allows tail standing of the light. Inside the tailcap there is no connections, the body of this light does not carry any current. The tailcap is mounted with good quality square threads. There is also an o-ring to make the light weatherproof.




    The light uses a battery carrier for 8 AA batteries. They are connected as two strings of 4 batteries.



    The carrier uses springs for connection to the light, both + and - are at the front end, the back of the carrier does not carry any power.



    The carrier has mechanical polarity protection at the plus pole.



    Here are all the parts of the light.


    This upgrade to the TK40 has higher output and is more focused, making it a good thrower. The side switches is easy to use in an underhand grip and Fenix has also reduced the standby draw to a more acceptable level. With these improvements I believe it is a good update and a good light for people that want to use standard batteries (instead of LiIon).



    Technical specification and measurements


    The light can work with alkaline, lithium and NiMH batteries and needs 8 cells (Fenix does approve of lithium in this light and recommend NiMH).

    Measured size and weight:
    Length: 215 mm
    Diameter: 40 to 62.6 mm
    Weight: 527 gram with eneloop

    The light uses a Cree XM-L led.



    In the above table I have collected all modes. I have also included off as a mode, because the light uses a small amount of power. All the estimated runtimes are with eneloop batteries. The estimated lumen are scale from the specified maximum and shows that high and med settings are close to specification. The brightness is a relative measurement from a lux meter or a light sensor (For flashing modes).
    All the values are measured at 4.8 volt.



    The voltage sweep shows a light with very good stabilizing down to 3.7 volt. The "funny" looking curve at 3.7 volt is my equipment that has some problems with the fast reduction in current draw.



    With high the stabilization works down to 3.3 volt and my equipment does also has some problems here.



    Medium stabilizes down to 3 volt.



    Low can stabilizes down to 2.7 volt.




    The good stabilization gives a very flat runtime curve, when the batteries are nearly empty the light drops out of stabilization and can keep a low brightness for a long time.



    The strobe changes between 6.8 hz and 15.8 hz with two seconds of each.



    The sos uses a 0.35 sec unit and it takes 11.6 second to transmit one sos, the pause between is 2.5 second.


    Comparison to other Flashlights

    Fenix TK40, Fenix TK41, Fenix TK45


    Fenix LD40, Sunwayman M40A, Olight M31 Triton


    For the full comparison to other lights with graphs and beamshots see here

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    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    Thanks

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    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    How do you know, how much the heatsink can handle?

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    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    Thanks for the excellent review.

    It's a shame that the main (+) spring has the cut end of the coil as the high spot. It's digging in and removing all the gold off the mating face on the head. With all that pretty flash gold over everything, it's a shame that it's already gone from where it's needed the most.

    I would consider a slim head version of this light, with the additional flood that comes with it. No molded plastic like the other Fenix, let the body be the heat sink. Batteries need to release heat too
    Last edited by EngrPaul; 05-15-2011 at 06:54 PM.

  5. #5

    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    Nice review HKJ, as always - very clear and concise, with tons of useful data and observations.

    Sounds like a winner overall. I never picked up the TK40, since I like a bit of throw in my high powered lights. And glad to see they've reduced the standby current to something similar to the TK45 (well, twice as high here, but since the batteries are 4x2 instead of 8x1, that works out to a similar 3.5+ years).

    Quote Originally Posted by EngrPaul View Post
    It's a shame that the main (+) spring has the cut end of the coil as the high spot. It's digging in and removing all the gold off the mating face on the head. With all that pretty flash gold over everything, it's a shame that it's already gone from where it's needed the most.
    Hmm, good catch. Part of why I like those solid metal reversible carriers that Sunwayman uses.
    Full list of all my reviews: flashlightreviews.ca. Outdoor 100-yard Beamshots 2011. Latest: Jetbeam RRT26.
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    Flashaholic* Samy's Avatar
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    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    I think i'm just about ready to get one of these, but i need something that doesn't have a 'tunnel vision' spot. I need need something super bright with plenty of spill/flood around it too. Does the TK-41 have plenty of spill? Photos never do lights justice. Otherwise i might wait for the TK70

    cheers

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    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots


    Is that your hand? It's massive, It dwarfs the TK41.

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    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    Quote Originally Posted by kj2 View Post
    How do you know, how much the heatsink can handle?
    I know how much it has to handle, the light uses up to 11 watt (But I did not subtract the power going out as light, it is probably 2 to 3 watt).

    Quote Originally Posted by EngrPaul View Post
    It's a shame that the main (+) spring has the cut end of the coil as the high spot. It's digging in and removing all the gold off the mating face on the head. With all that pretty flash gold over everything, it's a shame that it's already gone from where it's needed the most.
    The gold layer get scratched off on the outer ring too. I do not believe that this is a problem, there is a thick layer of metal, the springs has a decent pressure and any oxidation will be removed when screwing the light together.


    Quote Originally Posted by Samy View Post
    I think i'm just about ready to get one of these, but i need something that doesn't have a 'tunnel vision' spot. I need need something super bright with plenty of spill/flood around it too. Does the TK-41 have plenty of spill? Photos never do lights justice. Otherwise i might wait for the TK70
    For lots of spill you need the TK45. The TK41 has some spill, but I can hardly say if it is enough for you.

    Quote Originally Posted by Mr Floppy View Post

    Is that your hand? It's massive, It dwarfs the TK41.
    Yes, it is my hand, the same as I uses in all my recent reviews. I believe the size is about average around here.
    Last edited by HKJ; 05-16-2011 at 04:47 AM.
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    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    Great review and thanks a lot. HKJ

    TK41 looks very nice!

    The current on turbo mode seems 2.8A. Is it right?
    Is the screw of the head side squre threads too?
    Do you notice the batteries-rattling sound in the body tube?

    Thanks in advance.
    Last edited by candle lamp; 05-16-2011 at 12:33 AM.

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    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    Quote Originally Posted by candle lamp View Post
    The current on turbo mode seems 2.8A. Is it right?
    The maximum current it draws from the batteries is 2.8 A (Thats 1.4 A for each bank), but most of the time it will be considerable less (See red line on Turbo chart).
    The led is probably feed with 2.8A.

    Quote Originally Posted by candle lamp View Post
    Is the screw of the head side squre threads too?
    No.

    Quote Originally Posted by candle lamp View Post
    Do you notice the batteries-rattling sound in the body tube?
    I did not notice it, but then I did not try shaking the light.
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    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    Quote Originally Posted by HKJ View Post
    The gold layer get scratched off on the outer ring too. I do not believe that this is a problem, there is a thick layer of metal, the the springs has a decent pressure and any oxidation will be removed the screwing the light together.
    I agree with you on this. Because of decent spring force, the carriage would probably work just as well if it was nickel plated only and had no gold on it.

    Due to cost, the gold is most likely a soft flash, not a wear resistant hard gold. Gold is commonly used on the PCB to protect the solderability of the nickel underneath the pads (ENIG), not for contact performance. I see there is some soldering done on the carriage springs as well.

    Can't deny it was a good choice for looks. I wish the ends of spiral springs in flashlights would generally be less damaging to cells and terminals. It seems it's more cost effective to leave the cut end of the coil spring at the tip. I will be on-site at a spring manufacturer tomorrow and I'll ask them about end conditions of spiral springs.

    As a flashlight owner, if I see deep scarring on terminals or cells, I will deburr or re-bend the spring as needed.

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    Help Re: Review of Fenix TK41, with measurements and outdoor beamshots

    I know this is going to come across as a very noob question and I'm going to regret asking it, but I'm confused.

    In turbo it draws 2.8A, or 1.4A per bank of 4 cells. Doesn't this mean it draws 350mA per cell (1.4/4), so it should last >5 hours with eneloops? Obviously I'm making a mistake here because it doesn't in fact last that long but can't figure out what I'm doing wrong...

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    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    Quote Originally Posted by bbb74 View Post
    I know this is going to come across as a very noob question and I'm going to regret asking it, but I'm confused.

    In turbo it draws 2.8A, or 1.4A per bank of 4 cells. Doesn't this mean it draws 350mA per cell (1.4/4), so it should last >5 hours with eneloops? Obviously I'm making a mistake here because it doesn't in fact last that long but can't figure out what I'm doing wrong...
    Each bank is 4 cell in series, this increases voltage but keeps current the same.
    With banks in parallel the voltage stays the same, but the current increases.

    A simple example with two cells, each 1.2 volt 2000mAh:
    In series: 2.4 volt, 2000 mAh
    In parallel: 1.2 volt, 4000 mAh



    And again: The light does not draw 2.8 ampere all the time, but more like 2.2 ampere in average.
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    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    Ah thanks. So each individual cell is putting out 1.4A at ~1.2v hence the runtime. For some reason I figured that I needed to divide the current by the number of cells providing it, but now I get it. Now if I could delete my post...

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    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    Quote Originally Posted by EngrPaul View Post
    Thanks for the excellent review.
    It's a shame that the main (+) spring has the cut end of the coil as the high spot. It's digging in and removing all the gold off the mating face on the head. With all that pretty flash gold over everything, it's a shame that it's already gone from where it's needed the most.
    I would consider a slim head version of this light, with the additional flood that comes with it. No molded plastic like the other Fenix, let the body be the heat sink. Batteries need to release heat too
    On my TK35, there a some spots where the gold is gone. It still works, but it's a shame that it comes that easily off.

  16. #16

    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    Thanks for the review.
    We mostly come out at night...mostly

  17. #17

    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    In a real pinch, would it run on 4 cells in one string with reduced run time on low or medium? I assume that high or turbo would be too much current draw.

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    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    Quote Originally Posted by stickx View Post
    In a real pinch, would it run on 4 cells in one string with reduced run time on low or medium? I assume that high or turbo would be too much current draw.
    Yes, turbo will probably also work with eneloop (This mostly depends on the springs in the battery carrier).
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    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    Quote Originally Posted by HKJ View Post
    Yes, turbo will probably also work with eneloop (This mostly depends on the springs in the battery carrier).
    Have tried this and turbo still works on 4 AA's (Eneloops).

  20. #20

    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    Quote Originally Posted by HKJ View Post
    Yes, it is my hand, the same as I uses in all my recent reviews. I believe the size is about average around here.
    This is only one where I have a yardstick to measure your hand by. If I hadn't already seen the size of a TK41, I'd say it was a compact torch.

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    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    Quote Originally Posted by HKJ View Post
    Each bank is 4 cell in series, this increases voltage but keeps current the same.
    With banks in parallel the voltage stays the same, but the current increases.

    A simple example with two cells, each 1.2 volt 2000mAh:
    In series: 2.4 volt, 2000 mAh
    In parallel: 1.2 volt, 4000 mAh



    And again: The light does not draw 2.8 ampere all the time, but more like 2.2 ampere in average.
    Therefore Is the input voltage totally 4.8V (4000mAh capacity) in case of using Eneloop Ni-Mhs?

    Do we call it 4S2P?

    Thanks for your answer to my previous question.

    Best regards,

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    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    Quote Originally Posted by candle lamp View Post
    Therefore Is the input voltage totally 4.8V (4000mAh capacity) in case of using Eneloop Ni-Mhs?
    Yes. Just remember that NiMH has a nominal voltage of 1.2 volt, a freshly charger NiMH is above 1.4 volt.


    Quote Originally Posted by candle lamp View Post
    Do we call it 4S2P?
    Exactly.
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    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    Thanks a lot for your time. HKJ

    One more question please.

    How about the batterires connection for TK40, TK45?

    Are the both lights 8 cells in series(=8S)?

    I could get the above assumption from your TK45 review's table.

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    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    Quote Originally Posted by candle lamp View Post
    How about the batterires connection for TK40, TK45?

    Are the both lights 8 cells in series(=8S)?
    TK40: 4S2P
    TK45: 8S
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    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    As always

    Your reviews are always top notch!
    I've got more flashlights than I need, but still wants more...and then a few more

  26. #26

    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    Quote Originally Posted by Sharpy_swe View Post
    As always

    Your reviews are always top notch!
    +1
    good job.

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    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    Thankyou for the review. Out of curiosity I was looking at the cree xm-l specs.

    The XM-L maxes out at a max of 3A and a forward voltage of ~3.35V = ~10 watts. Your graphs show the TK41 maxing out around the ~10.5 to 11 watts mark, so after subtracting driver loss, it appears the led is being driven at about 100%.

    Note Cree say: "Cree currently recommends a maximum drive current of 1500 mA for XLamp XM-L white in designs seeking the ENERGY
    STAR* 35,000 hour lifetime rating (≥ 94.1% luminous flux @ 6000 hours) or 25,000-hour lifetime rating (≥ 91.8%
    luminous flux @ 6000 hours)."

    Cree also say that at 3A, the XM-L will be at 325% of the rated luminous flux (which is 280-300 lumens @ 700mA for the T6 bin) so 910 to 975 lumens at 3A. Given that Fenix say 800 lumens for the TK41 does that sound right? Only a ~15% drop in output from emitter lumens to ansi lumens??

    Again must be something wrong with my maths... but maybe not as xm-l peak out a touch above 1000 lumens with a U2 bin?

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    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    Quote Originally Posted by bbb74 View Post
    Note Cree say: "Cree currently recommends a maximum drive current of 1500 mA for XLamp XM-L white in designs seeking the ENERGY
    STAR* 35,000 hour lifetime rating (≥ 94.1% luminous flux @ 6000 hours) or 25,000-hour lifetime rating (≥ 91.8%
    luminous flux @ 6000 hours)."
    Flashlights are not designed for energy star ratings.

    Quote Originally Posted by bbb74 View Post
    Cree also say that at 3A, the XM-L will be at 325% of the rated luminous flux (which is 280-300 lumens @ 700mA for the T6 bin) so 910 to 975 lumens at 3A. Given that Fenix say 800 lumens for the TK41 does that sound right? Only a ~15% drop in output from emitter lumens to ansi lumens??
    You calculations looks fine to me and I agree with you that a getting 85% of the light out the front is a very impressive feat (If they use the T6 bin).
    Fenix might not even drive the light at 3A, if you look at my voltage sweep, it peeks at 2.8A. This does not have to be the led current, but probably it is.
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    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    Quote Originally Posted by HKJ View Post
    Flashlights are not designed for energy star ratings.
    I know I know, but am wondering how long a tk41 will actually last if its always in turbo. I'm thinking of getting one but would hate the guilty feeling when going exploring for a few hours in turbo

    You calculations looks fine to me and I agree with you that a getting 85% of the light out the front is a very impressive feat (If they use the T6 bin).
    Fenix might not even drive the light at 3A, if you look at my voltage sweep, it peeks at 2.8A. This does not have to be the led current, but probably it is.
    That 2.8A was at a voltage of about 3.7v or something though right, so at the xm-l's max forward voltage of 3.35v the current could be around 3A?

  30. #30

    Default Re: Review of Fenix TK41, with measurements and outdoor beamshots

    I read that the lux of the TK41 on Turbo is approximately 55,000. I am wondering how that transfers down to the lower levels. Is the formula linear (cross multiply & divide) or is there a different formula?

    Does 55,000 @ 800 Turbo translate to:
    23,031 @ 335 High? (335*55,000/800)
    7,425 @ 108 Medium? (108*55,000/800)
    688 @ 10 Low? (10*55,000/800)

    For those familiar with the Streamlight ProPolymer Luxeon 4AA, I believe it was about 3,000 lux @ 42 lumens, give or take - and considered a good thrower at those levels. Adding in 1 more comparison to the above list...

    2,888 @ 42 ProPoly Level (42*55,000/800)

    Does this indicate that it is about the same degree of thrower as the ProPoly (just able to go a WHOLE lot brighter)?

    -- just trying to get a handle on the throw at the lower levels...
    David

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