Hugsby P31 - Easy QTC mod host

I purchased a strip of QTC from 18sixfifty a few months back and since then I’ve been looking for a cheap host to try it out on. I prefer clickys to twistys so I was thinking maybe I could rig a light up to still use the clicky for on off and adjust the tail cap or head for light level. Enter the Hugsby P31, might work and cheap enough that I won’t mind if it doesn’t.

First off I need to apologize for the lack of pictures, I just lost my web-site hosting service and until I find a replacement I won’t be posting any pics (also means any pics in my previous posts will be gone as of 10/8). This mod is simple enough that I should be able to explain it.

I started by disassembling the head and stripping the driver down to a contact board. This driver has two boards, I stripped everything off the lower board (battery contact board) and threw the parts in the spares bin.
While I had the head apart I swapped the XR-E out in favor of a Nichia 219b on a filed down Noctigon. An XP-G to XM-L centering disk perfectly centers the Nichia in the reflector.

Now on to the tail cap. The P31 switch uses the usual spring with a brass cap to contact the battery held together with a threaded ring. The spring is not soldered to the switch board but held in place by a plastic spacer between the retaining ring and brass cap.

With the spring remove I reassembled the tail cap and measured the clearance between brass cap (touching the switch contact board) and several different batteries with the tail cap fully installed on the body. The longest of the batteries is a protected AW 14500, the shortest is a Titanium Innovations 14505 Lithium Primary, the difference between them is only about 1.0mm.

Clearance with the AW is about 1.0mm., the QTC is approximately 1.0mm thick uncompressed. All I needed to do was shim the brass cap a bit to compress the QTC.

I over-filled the brass cap with solder then filed-sanded smooth to my final height. I left the height on the high side because I have 4 of the 14505s to use up, once those are dead I’ll file down to AW height.
The QTC strip is 10-11mm wide, I just cut a 10mm round piece and dropped it on the switch board, place the brass cap inside it’s plastic spacer and secure with the retaining ring. There’s no place for the QTC to go and no worry about shorting the battery since it’s on the ground side. As far as I can tell QTC only conducts between the compression points anyway.

To go from full bright (tail cap screwed all the way on) to lowest level is less than 1/2 turn of the tail cap and since the switch is the primary on/off device wear on the QTC should be minimal.

Without the tail cap I placed the QTC on the battery - to check current, 0.38A with the 14505, 1.6A with an UltraFire Protected 14500 and 2.2A with the AW.

Output with the 14505 can be varied between 4-80 lumens, below 4 the light starts to flicker. With the UltraFire I got 40-290 lumens, I couldn’t really check output with the AW due to less thread engagement, that will be remedied when I adjust the brass cap for AW use.

I hope this makes sense without pictures.

Thanks for this. I was wondering which host would be the best for my QTC blocks (much smaller than yours) that I got off eBay UK.

I’m more of a visual learner, so pictures would have been appreciated, but it does still make sense without, just needs, for me, reading 8 times :slight_smile:

Nice mod. So you sound like a fan of this magic stuff. I keep seeing this plastic bag in my parts box thinking I must do something with it one day.

@ Splott-Light

It will make much more sense once you have the light apart in your hand. A word of warning though, taking the head apart is a PIA!

@ MRsDNF

There’s a certain cool factor to it but I don’t really think it’s that practical. There’s a threshold you must reach before current will start to flow, after that you can back it down a bit but not much. I can’t get it into sub-lumen output. If I was planning on using this light regularly I throw in one of those 167 mode, milli to mega lumen drivers the geniuses on this forum keep coming up with.

If the thread was finer do you think that would give better control? Instead of having half a turn from min to maximum say the thread pitch was two thirds smaller that would be 1.5 turns from minimum to maximum.

Yes, I think the finer the thread pitch the better for this purpose.

I also think more thread engagement (say 15 threads engaged when fully seated as opposed to 5) and high quality, close tolerance machining would help. When loosening the tail cap to dim the light the ground path is through the threads which are not providing any clamping force, loose threads provide an intermittent, hard to modulate ground.

Thanks for the info.