# What did you mod today?

Linear CC drivers work by burning extra voltage into heat. This happens in MOSFET, which basically works as smart variable high power resistor. So, MOSFET is NOT in fully conductive state all the time like on DD drivers.

Math for power dissipated in FET is simple: Pfet=(Vbatt-Vled)*Iled

Djozz' statement that "FET in linear CC drivers runs hot" is not accurate in general, how hot will FET be depends on three things:

1.Amount of power disspated in FET (equation above),

2.Thermal resistance Rth (C/W) between FET case and flashlight body - this constant tells us how many C degrees will FET get hotter for each Watt of power dissipated in FET(the lower the better)

3.Flashlight temperature.

Math is again relatively simple for steady state conditions: Tfet= Tflashlight + Rth*Pfet

Why move FET to LED pcb?

MOSFET on FR4 PCB has relatively poor value of Rth, I measured about 20C/W for 17mm LD-A4 driver without any thermal "improvements" like adding silicone fillers, so just driver in pill.

This means for each 1Watt of heat in FET, FET would get hotter by 20C. If you take worst case scenario where flashlight is already hot at 60C, to reach 100C FET temperature you need just 2Watts of heat Tfet=60C + 20C/W*2=100C.

That means max. allowed power dissipation should be declared as 2Watts@60C flashlight temp. FET can handle higher temperature, about 150C, but rest of electronic parts (caps,ICs...) which are on same pcb are rated to ~105-125C.

The reason for high Rth value is bad thermal conductivity of FR4 material combined with small cross section and relatively long distance through which heat must travel, and very small contact area between driver GND ring and pill.

Copper layers help a bit, but the main problem is that FET drain pad, which serves as cooling pad, must be isolated from GND ring - no direct copper thermal path is possible.

If you put MOSFET on LED PCB like mosX which has very high thermal conductivity, Rth between FET and flashlight becomes very small,<1C/W!

Thermal conductivity of ceramic dielectric is much higher than FR4 material, thermal path is much shorter(1.5mm), and cross section area is bigger. All this gives much lower thermal resistance.

If we do the same calculation as above for mosX PCB with Rth=1C/W, for 2Watts of heat in FET, FET temperature will be Tfet=60C+1C/W*2=62C! Temp. increase is just 2C, compared to 40C for FET on driver PCB.

I can see why some people intuitively think that it's better for FET to stay on FR4 driver PCB because it's "isolated/protected" from LED heat, but remember that LED PCB/shelf is also a great heat sucker!

As math shows us, FET on driver PCB would get much hotter (and by only its own generated heat), because it's too thermally isolated from flashlight cooling surfaces. Heat builds up as it can't go anywhere efficiently. FET on LED PCB would run much cooler because despite the heat generated by surrounding LEDs, there is still plenty of cooling ability caused by very low thermal resistance of LED PCB/shelf.

For those who still are not sure about all this, one little thought experiment: take two 20mm LED PCBs with any LED and place one on cold (20C) wooden surface, and other on hot (60C) aluminum/metal surface.

Drive LEDs with same current/power, let say 3Watts. What do you think, which LED will get hotter after few minutes?

(LED on MCPCB represent FET/heat generator, wooden surface is FR4 driver pcb, hot metal surface represent LED MCPCB)

My flashlights are liquid cooled at 98.6 degrees F. Sometimes the heat sink complains though.

Thanks Neven, that really clears it up for me. I know there are Toshiba MOSFET’s that have an additional thermal pad on top for just this sort of occurrence but adding a heat sink can be problematic as there is often very little space.

Thank you for going to the trouble. Appreciate it.

Finally got my 3x White Flats in my 18650 C8F. I had a virgin PCB from the 6 LED light I built. It was much easier to reflow on a new PCB with less solder and some flux.

With extra long 20 gauge wires (for re-flashing) and MTN-17DDm FET+1 driver. Both ends bypassed.

Get about 13.x amps on a lightly used VTC5D for 144kcd - way more satisfying than the shaved SST-20’s that were in there before.

Nice contactcr, I wondered how those would work in such a light…

[quote=DB Custom]
Nice contactcr, I wondered how those would work in such a light… ;)[/quote

+1!!

beam shot?

I went stripping again

I just couldn’t take the “baby blue” of my EDC01 anymore (nor my wife saying “awww… that’s cute”).

I took out the internals and stuck a cotton ball coated in Vaseline inside at the business end and covered the threads with it as well. I wiped the excess off with IPA and then have it a bath in lye (a solution prepared from granulated drain cleaner crystals).

I haven’t decided yet it I’m going to polish it. I think I’ll leave it for a while and see what happens.

Oh yeah, and I swapped a 4000K Luxeon V2 in it. Makes for a great “around the house” light.

Kinda cold for stripping. I like. I use suspension clip on my SAK

Put a new MOSFET on an odd driver this evening. Been a LONG time since I’ve done this! Why? It’s the huge 70N02!

Nearly doubled the output over their FET. Still a very long way from their claim of 100,000 lumens. lol

Sorry for off topic but needs opinions from the regulars here.

Looking for high quality angled tweezers. Ones that could remove a retaining ring if they had to.

Im replacing this model, only because i tried to pry with them and messed up the tip. They were otherwise very good. Just seeing if something else is out there

https://www.hozan.co.jp/E/catalog/Tweezers/P-887.html

Yesterday i was at the workshop from a friend (to weld a few parts together) and he had a Duracel LED light on his bench. Terrible led color (very white and for sure not high CRI) but a interesting reflector for a worklight. Would be interesting to see how a beamshot from a LED like the XHP50, LMZ9. . . looks like with this kind of reflector. I tryed to get one (it was very cheap and something interesting to play with) but the shop he bought the light (it was from the bargain bin) did not have the light anymore.

XHP50 does not look good in this flashlight.
I have bought mine from banggood.com, but it is no more avialbe: http://www.banggood.com/CREE-XM-L2-1A-1000LM-5modes-Long-Range-Tactical-LED-Flashlight-p-945461.html

Here I have some Info of my modding on this flashlight. I had different drivers and LEDs in it. XHP50, MT-G2, 2 burned XHP50.2.
Look in the text, there are some more informations as in this post, if you search for “banggood”:

If some one want to see the pictures an is not member of the TLF, please tell me.

If I compare your picture and my flashlight, I am not ready shure if it is the same flashlight, but my flashlight as a similar reflector with OP in the bottom and SMO at the top.

Put some XP-L V6 3D Leds on the RovyVon E300s!

Before (XP-G3 CW ) >>>>> After (XP-L V6 3D).

I brought my smashed led E14 back to life by throwing in a Mtn17dd driver combined with a triple xpl hi 5000k led setup. Fun first mod.

Nice pocket rocket! Way better than my first mod

Astrolux Ti3A Luxeon V2 5070 - FET 10 - 10440 - Fw Clicky Tail Sw - 930lm.

So this SupwildFire is a 7 XM-L T6 light with a pretty nice reflector, made in the form of a C8 but a big brother… it takes a 26650 cell. Has a lighted side switch that shows power level when running and has a micro USB charging port.

Oddly put together though. The emitters are on a pretty thick aluminum MCPCB that sits on a shelf, hollow pill… the driver is secured with 3 screws from INSIDE the light, down below the MCPCB. So, I swapped the MOSFET to the 70N02 which is more efficient, changed the leads to 18ga, cut an aluminum emitter shelf that is press fit into the top portion of the driver bay (cut the press fit area into the driver bay) replaced the XM-L T6’s with XM-L2’s in a mix of color tints… 3 warm white 3 cool white and a de-domed cool white in the center. Also bypassed the springs.

So now, after having seen 1368 lumens on a Basen cell straight from it’s twin still in stock form, this one makes 4823 on the same Basen and if I put a 30T in the fat tube it does 6603 lumens. It makes enough heat now to heat up the head in about 2 minutes.

L and M modes are quite high, with (on the Basen) Low coming at 1597 lumens and Medium at 2497. (Yes, it’s the typical driver UI the Chinese favor, H-M-L-S-SOS-Beacon.)

Pretty cool light, good price, nice reflector, just needs some tweaking to make it more productive. Of course, there’s nothing I can do to make it produce the 100,000 lumens they claim it makes…

Pics so it happened…

Straight out of the box… there are two of these so I attacked one and allowed the other one to watch.

Size comparison… I was talking to my buddy on the phone (he ordered these and had them sent here) as all this transpired so forgive me the sloppy nature of these pics, they were “on the fly” as it were…

So above you see the HD2010 and Convoy C8, here’s beside a Convoy L2…

Plastic threaded housing around the switch lights green when the light is on and the battery is at a fairly full level…

Same area lights red when charging via the micro USB port…

Will you look at this Monster spring in the tail? Steel, uncoated, won’t even accept solder. Had to wrap the bypass around the spring and solder to itself…

A look into the 7 cups of the reflector at the XM-L T6 emitters. The thick Aluminum MCPCB is at least made right such that the emitters are well centered, the centering rings are unusual, never seen their like, but they work well…

Showing the MCPCB with it’s emitters, some of the centering rings, and the white Fujik type glue holding the MCPCB onto the shelf…

The driver is secured with 3 screws from the inside, here’s the battery side view…

Fortunately they left an open slot where the charger boot plug comes into the driver bay, used this opening to punch the MCPCB up from underneath with a screwdriver…

The driver, with it’s new 70N02 applied… their FET has a 15mOhm Rds on time, the new one is 4mOhm Rds On. This is the one that started the FET craze with Comfychair leading the way what seems like forever ago…

Purple Haze, purple haze… an UV induced look into the new XM-L2’s arranged in a staggered WW/CW configuration with a CW de-domed center emitter…

A look into the reflector showing the new XM-L2’s without the UV light…

So, the plan is to build the other one better with a threaded thermal shelf and SST-40 emitters, probably on 20mm SinkPAD’s and tediously hand installed to match the reflector. Most likely with a piggybacked FET+1 driver running the show to get rid of this semi-horrid UI (this one at least lets you turn it off with a press and hold to avoid the cycle of blinkies, but you do have to wander through them at some point)

I think this was about \$23 on fleabay. My buddy saw them (18 emitters to 3, and everything in between) and of course he wanted me to try to hit the claims… on a single cell? Yeah, right!

Try harder

Sounds like a classic BLF mod Dale. Even without pictures