Modding dive light question

Lets go a different direction. Original light was rated for 800 lumens
Use 1x 26650 battery, original tailswitch (which still works ,low, high, off), a spacer for length rq’d to make up the difference between 3 “C” cells and 1 –26650 battery.
What led would you use to increase the light output?


What light output can I expect from this and where can I purchase it?

Depends but generally around 900-1100 lumens. The hi is meant for throw, not output. If you want max output, the regular xp-l or Samsung LH351D. You can get them from Kaidomain or Aliexpress.

Will the Cree xhp50.2 work? Give more light output?


I was hoping for a definite lumen output vs the XP-L HI

The XPL-HI is a de-domed XPL2 (IIRC). So I wouldn’t expect a substantial difference in terms of lumen output. The HI will have a smaller/brighter hot spot though.

Without knowing for sure what flux BIN they used, or if they used an XPL or XPL2… its hard to say for sure if an emitter swap will result in a lumen increase. You’ll have to try it and see. An old XPL in V6 flux BIN will still do ~1200 lumens at ~3A

Good Luck!!

Will the Cree xhp50.2 work? Give more light output than the XPL-HI?

Yes if its a 3V version:

It will result in slightly more lumens from the same driver. There could be some thermal stability benefits too, since you are essentially under-driving quad XPG2 dies.

Matt Smith did a similar mod (swap from a single die to the 50.2) in this vid and the lumen gain was around 12%. I personally dont think thats much difference in the field. The bigger difference IMHO will be in the beam pattern. That will be readily apparent.

We still have no idea what flux BIN XML they used on your OEM light so keep that in mind. Odds are its not the brightest though so an emitter upgrade should result in a slight but noticeably brighter light.

The details of Cree XHP50.2 3V - K2 1C on DTP Copper MCPCB say it may be damaged by use with an FET driver and high-drain 18650/26650 batteries!
How do I know what driver I have and what is fet?
Thanks for the response.

You’ll need to take it apart to access the circuit board(s) to answer that question. Post pics of it here and let folks comment on the driver circuit / components.

Mmm, I doubt that’s gonna happen…

Here’s some pics of driver led:

Just like I said, then. That’s only a contact board with bleeder resistors up in the head; it’s NOT a driver.

The driver is in the tail along with the magswitch.

Thats just a passive board with current limiting resistors on B+ and an old XML / XML2 emitter.

Any pics of the switch circuit board?

straycatboat, like most people here say, they are trying to help you but each flashlight is design differently and they need more information. You provide just the model but nobody else has same flashlight so they need more detail and photo to try to figure out how the circuit work.

From your picture, it look like lightbringer is correct that the top pcb is just a very simple current limiting pcb with just resistor to limit current. The original flashlight use a 3V led and three C battery (4.5V), so most likely it has simple driver circuit to run the led either through diffierent resistor or very simple pwm circuit. Because the switch is magnetic based and at the tail, the switch is most liekly similar to kramer5150’s seoulP7 light, or there is a very simple drive circuit.

You seem like you have motivation to modify the flashlight but do not have basic electronic experience, because you cannot power the 3V led directly from two 26650 battery with no modification and it will fry the led. You also cannot simply run a 12V led with two 26650 directly, it may light up but it will have poor performance. Until now we see no information or photo of the 12V led so we cannot try to figure out to help you. If you can take a photo of the tail pcb we can try to figure out how it work and how you can modify it to work with two lithium battery. Even so, most likely it will not be an efficient way to do it.

Converting three C battery to one or two lithium battery is not super easy because the voltage are very different, and most likely you will need to install a new driver circuit to run the led efficiently.

If cost is concern for you, my recommend is actually to buy a new flashlight, for example Sofirn SD05:

It is over three time as bright as your original flashlight but much smaller. If you run it at lower power level, it can also many hour as well. It is only $40, which will liekly cost the same as if you buy extra led or electronic drivers to try to modify your flashlight. Anyway if you most more picture, we will try to help.

I hope these pics are working, I think I figured out how to post the URL

These are pic of the tail switch and the original LED I burned out with 2x 26650’s:

Better pic of PCB in tailswitch\_RXIRtwDeX8NadyC_cZccb/view?usp=sharing

This is the most useful picture: IMG_1048.jpg - Google Drive
Sadly, it is blurry. Can you take a close up picture of the pcb with electronic component?

(edit - thank you for posting clear photo)

Most likely there is some voltage regulator or zener diode to protect the microcontroller from overvoltage. The microcontroller is most likely the 8 pin soic package. Because there are current limiting resistor on the top of flashlight, I guess the micronctroller using PWM dimming for brightness control. It may also sense that because the voltage is too high when you connect two 26650 battery, that it does not operate.


I think power come from outside ring (because this is tail pcb), goes through diode D1 for reverse protection, then through RC filter R2 and C1 and to voltage regulator Q1. This power the microcontroller (big 8pin IC), which controls brightness using a mosfet (Q1). R1 is gate pull down resistor, and C1 is some sort of big capacitor for off-time measurement for mode change. This means that the system use mosfet as switch and a resistor for current regulation using the pcb at the top of the flashlight, and brightness control using PWM. Most likely the best mod you can do is to convert flashlight to single 26650 and change the resistor on the top of the flashlight to slightly lower value because three C battery is 4.5V but one 26650 is 2.8V to 4.2V, to get same led brightness.

The led don’t look like real cree led, maybe cheaper copycat lattice bright led. For better performance you can use this one with 20mm pcb which look like it is good and easy led replacement:, and will be brighter. You can find different color on kaidomain if you want to change to warm white, or even cooler white.