I just swapped out the older driver with Sofirn’s replacement driver and measured it with both Samsung 40T and 30T and got 2,870 lumens at 1s. Basically no difference at all 
Check if the driver ring is making good contact like Jason noticed on his? Solder blob or shim it if not. I would probably redo the spring bypasses too with 20g
First of all, we can’t expect a 920 lumen boost just by going from an 18650 to a 21700 battery. Sofirn seems to have overrated it at 3500. A more accurate rating would be 2900 to 3000 lumen.
I wonder if there was nothing wrong with the original FET? Maybe it was just a bad connection with the driver retaining ring?
When I swapped my FET, I of course retightened the retaining ring. I saw 2 extra amps at the tail. I assume this is from the new FET.
With the Sofirn battery:
Stock driver about 7.2A at tail
After FET swap about 9.3A at tail
Later I measured 7.7A
I fiddled with the retaining ring and got 9.6A
So did the new FET help or was it just the retaining ring?
At 9.6A I was getting about 2900 lumen so that is about all that can be expected. Let’s say 3000 lumen at Turn On.
Yours seems to be performing pretty close to what I would expect. Only 300 lumen less at Turn On with the 30T. Try messing with the retaining ring to see if you can get a few more hundred lumens.
I can see your results are inconsistent. The VTC5D is a good high drain cell. I don’t think it should be 400 lumen less. All 3 of your tests should be about 3155 lumen. My guess is it’s the retaining ring. Get it tight.
If you want an extra 200 to 300 lumen boost, try swapping the led wires to 18ga. I was seeing 3300-3400 lumen with this change.
Upgrading the driver spring bypass wire might squeeze a bit more.
Ps, I see in my notes that the driver retaining ring had a little bit of glue on the threads from the factory. Maybe this glue residue is hurting electrial contact?
I wasnt trying to compare difference between 40T and 30T. The replacement driver did absolutely nothing. I couldnt fet tje reflector out to replace the wires. The reflector is glued tight. I will try playing with the retaining ring
Just in case you missed it the reflector is screwed in. Take out the driver and its dead center in the shelf from the underside.
oh you’re right. Oh well, I’m too lazy to redo it now.
Neither was I. Sorry if I gave you that impression.
Hmmm the ramping on this is weird.
If I double click to Turbo I can’t hold to ramp down, I first must click to return to previous mode or press & hold switches it off. If Turbo is reached through ramping then it behaves as expected. Also while on Turbo any additional double presses causes a drop and fast rise to turbo again. It shouldn’t do anything if already on Turbo.
Very annoying
It’s seems to be designed to give a smooth ramp up to turbo over a second or two when double clicked. There’s not much of a need to double click if you are already ramped to the top, so that shouldn’t be an issue. I do prefer an instant jump to turbo. I’m not sure why they did this.
I haven’t tried to ramp down after double clicking to turbo. I guess I haven’t needed to. I usually use it at a lower level, then double click to turbo for a very short time then single click back to the memorized level.
No UI is perfect. If it’s really bothersome, Lexel should be offering some 21mm drivers soon. A 20mm will fit if you modify the retaining ring. Then you’ll have some other UI options. :+1:
I guess it’s not too bad, just took a bit to get used to after using the Q8. On the NarsilM you double click to Turbo and can ramp down from it.
I imported the new C8F to sell so wasn’t sure what to make of the double click flickering at Turbo.
What’s the red stuff they’ve covered over the solder on the driver for the switch wires?
I have no idea. I haven’t looked at it close.
It looks like strain relief for the joints.
The replacement drivers do not have that red covering.
Kawi, your brite work a little bit back is stunning! Excellent work man! Really slicks up the all black light, for sure….
Thanks Dale! 
Got bored during a 24hr machine endurance run and the shop lathe was in the isle next to it. Didn’t notice the plant manager was standing behind me, he’s like a Ninja, scared the hell out of me, when I heard somebody say behind me…wow that’s beautiful… I jumped he jumped 
He’s cool, borrows lights from me all the time, needs to buy a couple the money he makes…… :money_mouth_face: I let him borrow it the weekend before opening day, he brought it back, this is way too much light for me, got anything smaller? He loved the MH20GT… sent him a link and code, he can get his own. 
Agree, that C8F 21700 treatment is awesome! I got 351D 4000K 90 CRI's is my first 21700 host, just ordered a 2nd host. Really like how the XPL HI V2 5D's look in a triple, probably will do them in the next. Ohh - just noticed Richard is low on them - order 6 of last 8 just now...
I doubt the problem was the original FET.
According to the markings (2D030L) the old one is the NXP PSMN2R0-30YLD, which has a Rdson of about 2mOhm. That’s already really low. No way changing that to any other FET could gain 2 Amps, except the 2D030L
- is fake,
- is defect or
- was soldered badly.
But I assume you found the real flaw with the retaining ring. And I lift my hat for that, because that would be a design flaw that’s very easy to overlook.
My fix would be to file down the lower part of the threading of the retaining ring in a 45° angle, so that enough threading is left but the ring can sit lower. That should give good contact.
Hey Tom, nice to see you… hope everything’s been all right… been a while! 
I have a C8F v2 host I ordered right when they first became available. I haven’t managed to finish building a light with it, but I check the driver I plan to use with it for fit. The PCB is one of the Oshpark 2oz copper boards, which are really thin (0.8mm). The retaining ring clamps down nice and tight.
So, bad driver/ring fitment may be a problem for some lights, but not all of them.
Regarding the “filing down the lower part of the threading of the retaining ring” — may I request a photo or illustration of which part should be done? Sorry, I’m not really into modding and have not-so-good skills but would like to see if that can help the relatively low amps on the C8F 21700. Thank you.