-The 20mm KaiDomain MCPCB is not shaped the same as most others, so if your host has MCPCB hold down screws, the wire holes may not line up perfectly, they may be partially covered.
-The mtn 17mm fet driver comes with a >6mOhm resistance fet (IRLR8726TRLPBF) which is not ideal for such a high amperage application. I’d suggest a <2mOhm one: Sir178DP, BSC009NE2LS5ATMA1, Sir404, etc. Mtn used to have Sir404 on hand so you could try and request that. I’d assume mtn’s boards use 1oz copper. Ideally you’d want 2oz traces for this application. The mtn boards also do not have transient suppression (aka R5) so the MCU is going to see a pretty large voltage spike when turbo kicks on.
-Building a Del driver or Texas_Ace driver may be a good way to go. If you buy a 2oz board from Osh Park, they are 30 mil thick instead of 60 mil. Soldering a solid core wire around the rim can make up the difference, in lieu of a machined spacer.
-The Omten 1288 switch (found in S2, C8, etc.) isn’t exactly built for 20 amps. Ideally you’d build a fet tail switch like GFS16, but this is not the easiest thing to accomplish. Acquiring the components requires purchasing from two to three different sources, and it’s tricky to solder. The easier alternative is to use an E-switch host.
-You’ll need to bypass your springs so they don’t melt.
-A 21700 E-switch host would probably be the best way to go. I’m not sure what the options are for such a host.
People have pushed the Omten 1288 really hard and it survives. I suppose it’s a question of how long it will survive. IIRC, one of the lights being sold with the SFN55.2 LED in it has a mechanical tail switch, a 1.5A rated forward clicky. I’m not sure where I saw that.
The Sfn55.2 draws 30 amps easy with a stout battery, good current path, and a low resistance fet. That current will just about instantly overwhelm a C8 and you will pretty much be limited to any mode but Turbo. I’ve tested a few of these and they’re no joke. Even big hosts like the Nightwatch NI03 heats up really quick. You could try the sfq 60.2. It’s a 7070 size xhp70.3 HI clone. It’s still plenty bright and runs on 3v. If you must use the sfn55.2, grab a host like the L21A or M21D. The Omten 1288 (if genuine) is a sturdy switch. The PBS101 is a 125v 2 A switch that will hold up much better.
Another option with regards to the switch situation is to bypass the switch PCB and use the light as a twisty. The tailcap and/or body threads of the host need to be anodized. A zero res switch is another solution, as Matt shows here.
Thanks, I ended up ordering a M21C with a mountain 22mm 7135+FET driver. Initially I’m going to use the bypassed stock switch, but at some point I do want to try building a zero resistance switch. I have a few spare clickies and not a lot of spare time at the moment. I never did get an answer from mountain about a lower resistance switch (edit: driver) but that’s something I’ll consider changing in the future as well.
I recommend an omten pbs101. It holds up under the 50 amps of the NS59V1 just fine. The FET in that mountain driver isn’t the greatest will limit output a bit. You won’t reach 50 amps with a single snf55.2
There aren’t many off shelf 20A drivers around. Lexel used to be the source for those, but he’s been absent from BLF for over a year. Mtn is the only place I know of for pure fet drivers capable of more than 10A. You are limited to a 17mm driver in the host, so that doesn’t help either. You may try to source one from another flashlight like a Sofirn, Astrolux/Mateminco, but those are mostly 20mm and up.
Kaidomain delayed delivery of the SFN55 for a bit, but in the meantime I did receive my M21C host and some PBS101s. I’m happy to say that the PBS101 does (barely) fit!
Here’s the original switch sitting on the 20mm board.
And here’s that same shot with the PBS101 mocked up.
I managed to get one attached without melting the case too much. I don’t think you could fit anything bigger than a PBS101 on this board.
Bypassed the spring while I was at it.
The whole thing barely fits in the tail cap for the M21C. I had to remove the spacer from the switch assembly to get the retaining ring on, so the button actually sits in the silicone boot. I’m sure this makes the boot less water resistant but the button makes contact across most of the surface so I’m not too worried about durability. I ordered another board and still have some PBS101s so I’ll try to build a cleaner one later, but hopefully this will be good enough to drop the SFN55 in when it arrives, at least for proof of concept.
I finally got this light all together! It’s not a pretty beam, but the output is pretty intense. In the M21C I think it’s a great balance between throw and flood.
Mountain 22mm 7135+FET with Bistro. I lost moonlight shortly after installation. Maybe too much current? It doesn’t matter much with this light but I do wish I had gotten a picture of the 9 cores lit dimly.
Fisheye shot. There’s a lot of purple from the Convoy AR lens, and a distinct ring from the stainless bezel. I don’t mind it in use on this light though.
Not much depth on this shot but it does throw far.