Fenix TK50 will not go into low using Alkaline batteries.

Bicycleflyer

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I just bought a brand new Fenix TK50 that uses 2 D-cell batteries. When using NiMh batteries it works just fine. But when I switch out to a set of Good quality alkaline D-cells, something peculiar happens.

The way the flashlight is supposed to work...

In normal mode the light cycles low-mid-high-turbo, then back to low again

What happens with alkaline batteries.....

In normal mode the light cycles mid-mid-high-turbo, then back to mid...No low :(

Any ideas what is happening...is it the higher voltage of the alkaline. Fenix states that alkaline can be used. I could go on happily with just NiMh, but I need the backup option of alkaline batteries. If it wont go into low, then it is not very useful to me.

Your input is appreciated...
 

tre

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hahaha. I guess all the Fenix lights have this problem. The LD20 and LD25 do this. Alkaline cells initially have a higher voltage than NiMh cells. Low will come back after the alkaline cells are used for a while (the voltage drops). My opinion of Fenix lights is dropping by the day.
 

Scubie67

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Yeah, I guess this is also the reason I can not use Eneloops in my Smoke/Carbon Mon. detector(I have tried).The lower voltage registers the low battery alarm on the detector within a day or two after installing the NiMH batteries even though the batteries are freshly charged. I still have to buy regular 1.5 volt alkalines for this purpose although Eneloops go in my TV/DVD/Cable remotes,Thermostat,Alarm Clock and any other thing around the house I am forgetting.Digital Regulation does have its drawbacks along with the good it seems.
 

candle lamp

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As tre mentioned, you can't see the low mode with fresh alkarine batteries due to the higher voltage.
After 3~5 minutes, the light works well. It's normal.
 

John Spartan

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Interesting...I haven't had that problem with a TK50 I picked up recently. Used new Duracell alkaline batteries. Worked in all modes from the start.
 

Lanque

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Low and Medium on my TK50 looked almost the same with fresh Duracell alkalines. It took a while to drop to its proper low output. I only used alkalines as a test when I first got the light, and have been using D-nimh ever since. Low is still a bit higher than normal if the cells are fresh off the charger, but it settles down fairly quickly.
 

kramer5150

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just confirming what others have said. This is normal for many Fenix LOW modes, when Vin > Vf for the LED. Your low mode will return once the cells V drops a little.

Alkalines are risky in these lights anyways, with their random leak-prone nature... LSD-NiMH or Lithium primary is always a safer option.
 
Last edited:

Bicycleflyer

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Thanks for the replies folks. You confirmed what I suspected. When I get back home in two weeks, I may reinsert the D-cells and see how long it takes to drop the voltage down enough to get back the low mode. I did plan to use NiMh from the beginning. Better performance and lighter weight. I just need the alkaline backup option in case I find myself in some backwater location on the globe. If I have to run it in high mode for five minutes to drain a bit of voltage, then that is not too much of a burden.
 
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