Mod: Quad dedomed XPG2 C8 with 20700-bored tube

Man that looks really good. Nice work!

Nice work EasyB! Impressive LED work with the wiring and reshaping of the MCPCBs. Looks like and awesome flashlight.

Thanks for the comments.

By the way, I got the idea to bore out the C8 tube from DB custom: 20700 Batteries What is real? - #195 by EasyB

I bored the tube to about 0.810” ID. This leaves only about 0.008” wall thickness at the thinnest part which is the o-ring seat. :open_mouth:

Very nice mod EasyB. This is certainly different to the run of the mill C8. :+1:

Awesome work EasyB. :+1:

very nice!

Good stuff :+1:

Impressive!

Nice work on getting the MCPCBs and optics to fit. Good stuff indeed!

Thanks for the comments. :slight_smile:

I received the 20700 cell today. With this NCR20700B cell it pulls 9.7A instead of 10A with the 30Q. The tube is just long enough to accommodate the longer cell.

I am confused about something now, though. I measured the output again and the measurements are inconsistent with previous measurements. When I first built the light I took a measurement before I bored out the bezel or received the AR lens. With a 30Q this initial measurement was 2880 lumens at 15s and 77Kcd at 30s. Then I bored out the bezel, installed the AR lens, and adjusted the focus of the TIRs some because I noticed the focus was not optimized. I then did a measurement with the same 30Q cell (after recharging) and got 3040 lumens at 15s and 90Kcd at 30s, the numbers I quoted in the first post. The output increased by 6%, which is consistent with the change to the AR lens. The throw increased by more, which is consistent with the additional focus adjustment which would increase the throw but not the output.

Today, with nothing changed in the light I did another measurement with the same 30Q and got numbers very similar to the lower initial measurements. The measured current is the same as before. I tried another tailcap/switch just in case something changed in the switch to lower the current with the tailcap installed, but it didn’t change anything. So, I can’t explain why the measurement is lower now. Measuring other lights suggests my meter is reading fine now.

Wow, i didn’t think it was possible at all, to bore a C8 out for a 20700.
How did you do it?

Using a boring bar tool on a lathe. Like I noted above, the tube wall is pretty thin now in some places. It is definitely not possible for lots of 18650 tubes. It turns out I didn’t have to bore the tube out as much as I did, though. The 20700 cell rattles just a little bit now.

It takes a bit of time but a drill bit wrapped with tape and 180-220 sandpaper will work just fine. Wrap the tube with tape for a better grip and wear gloves, mask, and eye protection as it gets hot with fine aluminum dust. You want a snug enough fit that you can just get the tube over the sandpaper and hold it still against the torque. Add tape under the paper as the bore increases and figure on using most of a sheet.

I have used a spade drill bit in the past, which works quite fast, but it’s a bit dodgy… :smiley:

Probably the nicest c8 mod I’ve seen.

Very cool mod :sunglasses:

Shame the measurements are not consistent, sorry I can’t help with that.

I replaced the dedomed XPG2s with sliced SST20s, hoping to get some more output. It pulls 15.3A (with VTC5A) measured using a 10mOhm shunt replacing the tail cap. It does around 3900 lumens at start and 3700 lumens at 5s and 92kcd at 10s.

Right after I changed the emitters I measured the current and it was only 12A. Based on the emitter forward voltage and estimated circuit resistances I estimated it should pull around 16A, so I suspected there was some extra resistance somewhere, around 16mOhms. Sure enough I found it the first place I checked, between the driver ground and the head/tube threads; 15mOhms. This driver is one with the thinner PCBs from mtnelectronics. I had put solder blobs on the ground ring so it made good contact with the retaining ring, and it seemed like it was making good contact, but apparently it wasn’t. I beefed up these blobs with pieces of copper wire and got the resistance down to 1mOhm. I think the bad ground ring connection must have been the reason for the inconsistent measurements I described in earlier posts. Anyway I am very happy to have boosted the output of this light and to have figured out the source of the low/inconsistent performance I saw before. :slight_smile:

The oxide layer that forms on most solder is likely a cause for the increased contact resistance. For this reason, I’ve stopped using solder blobs for contacts wherever possible. Instead, I’ll solder on little brass or copper discs/bb’s to make the contact surface less oxidation/abrasion sensitive. DeOxit D100 works great as well.

8mm x 2mm magnets with grey paste (GD460) under seem to work fine too.
I’ve got several flat tops using them.

Copper and brass certainly tarnish, maybe faster than leaded solder?

Neodymium magnets can add a lot of resistance. You might want to take some measurements to make sure they are doing what you expect. If they work good enough for your needs, then that seems fine.