Fenix TK21 U2 LVC?

Hi guys,

Quick question please.

I have a TK21 U2 model and am extremely happy with it, i'm looking to buy a couple of spare 18650 batteries though and would like to know:

Does the torch have a built in Low Voltage Cut-off (LVC)?
If so does anyone know what voltage it is set to cut in?



Cheers
Mark

I know that Fenix have built-in protection. But on how much the cut-in is set, i don't know.
If you want a good answer to your question, I guess you have to email Fenix. Normally they response with a answer in 2-3 days.

Thanks for the response :thumbsup:

I took your advice and contacted Fenix directly, an absolute pleasure to deal with.
Fast responses to my questions, with good detailed answers, well done Fenix :thumbsup:


To sum up:
The TK21 U2 HAS a LVC, it's set to 3.3 volts.

I also asked regarding the TK35 as i have one on it's way.
The TK35 does NOT have a LVC, so it's better to use protected cells with the TK35.


Not really on the TK21 topic, but i also asked if i can use 10440 cells with my LD01's.
The answer was no, the voltage regulator will not support the higher voltage given by the Lithium 10440 cells.

Last question i asked was.
If i use CR123 cells instead of 18650's in my TK21, TK35 will the higher voltage give a higher light output.

The answer was no, as the lights voltages are regulated, so the light output stays the same.

So all in Fenix was a pleasure to deal with so far :thumbsup:

kwak said:

Thanks for the response :thumbsup:

I took your advice and contacted Fenix directly, an absolute pleasure to deal with.
Fast responses to my questions, with good detailed answers, well done Fenix :thumbsup:


To sum up:
The TK21 U2 HAS a LVC, it's set to 3.3 volts.

I also asked regarding the TK35 as i have one on it's way.
The TK35 does NOT have a LVC, so it's better to use protected cells with the TK35.


Not really on the TK21 topic, but i also asked if i can use 10440 cells with my LD01's.
The answer was no, the voltage regulator will not support the higher voltage given by the Lithium 10440 cells.

Last question i asked was.
If i use CR123 cells instead of 18650's in my TK21, TK35 will the higher voltage give a higher light output.

The answer was no, as the lights voltages are regulated, so the light output stays the same.
So all in Fenix was a pleasure to deal with so far :thumbsup:

Click to expand...

First I want to say; Fenix rocks!!

second; It's always better to use protected batteries. It's just saver for your light(s).
But it is strange that Fenix does put LVC in the TK21, but not in the TK35.
But like I said, (I) always use protected batteries, so no problems for me

Wow that's some great info.

My gut feeling is that the TK35 lack of protection is due too the fact that it's a 2 cell configuration minimum

kj2 said:

First I want to say; Fenix rocks!!

second; It's always better to use protected batteries. It's just saver for your light(s).
But it is strange that Fenix does put LVC in the TK21, but not in the TK35.
But like I said, (I) always use protected batteries, so no problems for me

Click to expand...

Aye i was pleasantly surprised.
They answer the same night and couldn't do enough to help.

I prefer to use unprotected batteries as the AW 18650's i'm currently using only charge up to just over 4.10v.
I've tried them on 4 of my chargers now and always get the same result, so i'm guessing the cells voltage protection board is kicking in before the charges reach full charge.

Granted 0.1v is neither here nor there.
But if the torch has a low voltage cut-off anways, i may as well save some money and buy unprotected cells.
That way i get a few seconds extra runtime plus i get to save a few quid at the same time.
win win

CarpentryHero said:

Wow that's some great info.

My gut feeling is that the TK35 lack of protection is due too the fact that it's a 2 cell configuration minimum

Click to expand...

I'm curious as to your thinking behind that please?


In my experience low voltage protection is just as important no matter the quantity of cells installed.
Drop a cell much below 3v and it's pretty much ruined from there on in.

If the LVC was set much lower than 3.2v/cell then i'd start to worry about one cell dropping out of balance to the other, as from around 3.2v the difference in each lithium cells discharge rates tends to change drastically.

This coupled with the fact that if the torch had a low voltage protection circuit it'd obviously only be able to tell total voltage of both cells not individual cell voltages.
So if the torch had say a 6.4v low voltage cut-off (3.2v per cell) you could have 1 cell drop to say 2.8v while the other is at 3.6v, both giving 6.4v still but 1 cell now effectively ruined.