SF Stratum, What is the LED's working Voltage?

Hi all,

I have a Surefire Stratum and I want to know the working voltage. Specifically, I would like to know the lower limit more than the upper. But if you happen to know that too...great. My reason for asking is I recently decided to bore the body out to accept an 18650 cell (my first mod). The flashlight was originally designed to use CR123 X 2 which is 6 volts and the 18650 is only 3.7... so can I expect shorter run times with the 18650? Performance wise the 18650 seems to do as good as the CR123s. I don't have any special equipment to measure this, but I took the flashlight outside and ran it with both types of batteries and the brightness seemed the same. The 18650s I am using are Ultrafire 3000 mAh protected cells. I know asking about expected run times when using a rechargeable battery seems silly, but I am just curious.

Any answers, thoughts, and suggestions are appreciated.

The only real way anybody knows the answer to this is to turn it on and let it run until it shuts off, and time it.
That is how people determine their actual run times. And since you are probably the only person in the world with a light like that, you'll probably have to do it.

Since it is a two-cell 123A light, I would expect it to be buck-only. That means the battery voltage must be greater than the LED forward voltage, so you'll be fine with any battery with more than ~3.3V.

If you have a multimeter that can measure current more than 1A, you can make a rough estimate of runtime. However, since you are using UltraFire cells, you don't have a reliable battery capacity rating to estimate with...

when the light runs the same with the single cell, then runtime with the 18650 will be better, as it houses much more energy than the 2 * CR123
--> have light run for 15 mins, then open back end and measure Ampere flow.

if that is Your light:
http://www.candlepowerforums.com/vb/showthread.php?277095-Surefire-Stratum-(S2-BK-WH)-Review
... then its an old Luxeon K2 led - outdated by todays standards (imho never really appreciated, but thats just my opinion probably)


I guess it will be about the same output and possibly slowly fading away when the voltage of the single cell gets too low, but that could "only" be measured (and possibly be seen, but not for sure) while You have the light run ...


PS: looks this thing can house "P60" inserts, so IMMEDIATELY switch to a led insert from member nailbender
(I recommend a XP-G2 insert now, as I am in the moment stepping back from the XM-L inserts to these. Think the added runtime covers for the thigher beam)

According to the datasheet, it has a typical Vf of 3.42V, ranging from 2.79V to 4.23V. The led seems to be driven at 1.5A to achieve the output of 160 lumen. With a buck driver You will need a battery voltage above the leds Vf plus the voltage loss of the driver. My conclusion is, that it might be possible to get a decent runtime with single LiIon cell if the Vf of the individual led is not too high and the battery keeps a high voltage at 1.5A current.

Thanks everyone, you gave me plenty of info and ideas.

@Yellow, Yes that is my flashlight and it does not accept P60 inserts.