Review of Fenix TK41, with measurements and outdoor beamshots

HKJ

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[SIZE=+3]Fenix TK41[/SIZE]

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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.

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

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

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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.

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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.

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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.

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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.

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

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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.

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

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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.

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The carrier has mechanical polarity protection at the plus pole.

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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).



[SIZE=+2]Technical specification and measurements[/SIZE]
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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.

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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.

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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.

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

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Medium stabilizes down to 3 volt.

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Low can stabilizes down to 2.7 volt.


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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.

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

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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.


[SIZE=+2]Comparison to other Flashlights[/SIZE]

Fenix TK40, Fenix TK41, Fenix TK45
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Fenix LD40, Sunwayman M40A, Olight M31 Triton
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For the full comparison to other lights with graphs and beamshots see here

.
 

EngrPaul

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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 :)
 
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selfbuilt

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

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).

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.
 

Samy

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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
 

HKJ

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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).

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.


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.

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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.
 
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candle lamp

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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.
 
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HKJ

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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.

Is the screw of the head side squre threads too?

No.

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.
 

EngrPaul

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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.
 

bbb74

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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...
 

HKJ

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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.
 

bbb74

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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... :)
 

kj2

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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.
 

stickx

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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.
 

HKJ

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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).
 

Mr Floppy

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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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