Monthly Archives: May 2018

Custom Triple LED MCPCB Technique

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I’m trying to build a triple emitter flashlight, but not just any triple emitter flashlight. I am not taking the path of least resistance, which has presented some challenges. But first, these are some of the salient details of what I’m trying to build:

  • SST-40 Emitters
    • Same 5050 footprint as the common XM-L & XM-L2 emitters.
    • Better beam, less tint shift than an XM-L2 when used with a reflector,
    • More efficient than an XM-L, XM-L2 or XP-L.
    • Lower forward voltage than XM-L, XM-L2 and XP-L
    • Only available in cold-white (6500K or 7000K), but the tint is pretty neutral
    • Taken together, these characteristics make for an emitter than can be pushed to almost 2300lm @ 7.5A/27W off a single Lithium ion battery.
  • Triple reflector: The simple path to a triple-emitter build is to use a triple-optic, but the available options don’t really give the spot+spill beam pattern I’m after.
  • 26650 battery: Sofirn sells a great reflector-based triple emitter C8F host for just ~$14, MCPCB included. I have one. There are two problems with it. First, the provided MCPCB is for 3535 form-factor emitters. Second, it can drain any cell in no time, but 18650s have ~2/3rds the capacity of a 26650.

I have a reflector, and a host I can fit it to without much trouble. What I don’t have, and haven’t been able to find, is an MCPCB I can mount 5050 emitters to in such a way that they’ll line up with the reflector. I think the Noctigon XP32 has the right spacing for the reflector, but it only takes 3535 emitters. I thought I might have found a 32mm MaxToch PCB that would work, but it doesn’t.

My fallback plan is to solder some 11mm Sinkpad MCPCBs to a copper disc. The difficulty is getting them positioned properly and then keeping them in position while soldering them down. I’ve explored various ideas as to how to manage this feat, and I tried one yesterday.

I started by making a template in inkscape. It was a little tedious. Inkscape isn’t really made for technical drawings, so I had to double check dimensions and adjust alignment and sizes repeatedly. Once I had something I thought would work, I printed it onto some index card stock. Next, I smeared some non-corrosive silicone adhesive on the template, and positioned the little MCPCBs face down on the template. I pushed them down firmly, scraped away the glue around them with a toothpick so I could get a better view of the template, and then adjusted them until they were aligned as best I could.

A few hours later, after the glue had set, I double-checked the alignment, then I cut most of the paper away, to clear the way for my soldering iron.

I prepped the copper disc and the exposed metal bottoms of the MCPCBs by tinning them. I used lead free solder because I wanted something with a higher melting point than the eutectic sn63pb37 solder paste I use to reflow the emitters on to the MCPCB. I had trouble getting a nice even, thin, layer on the copper disc, so I filed and sanded the solder surface down before continuing.

I put a thin coat of rosin flux on the tinned surfaces of the copper disc and MCPCBs, and centered the MCPCB cluster on the disc. Then I heated the disc with my soldering iron. Once it was hot enough to melt solder, I fed solder wire to each MCPCB while keeping the copper disc hot with my soldering iron. Once they were all nicely flooded with solder, I tweaked the alignment with the center of the disc. Removed the heat, and pressed down evenly with a block of wood to get a nice close fit between the copper surfaces. Once it cooled down, I removed the block.

The first time I tried, the alignment of the MCPCBs was off center a bit, so I heated things up and tried again. This time the results were a little better. As you can see, the paper charred a bit, but I think it still did its job of keeping the three MCPCBs positioned relative to each other during the process of soldering them to the copper disc.

I peeled the paper and silicone adhesive off with tweezers, and then rubbed the remaining adhesive off with a cloth. This is the result. I’m pretty happy with it. Or I would be, if, after all that, everything was aligned properly with the reflector. It’s not.

I’m not sure what, exactly, went wrong. I think I had the spacing right on the template. I think the main source of error was probably in getting the MCPCBs aligned to the template while glueing them down to it.

I think that I’m just going to try reheating the assembly again and adjusting things until they line up better. If that works well enough, I’m just going to call it good and finish building the light.

If I can’t rework it well enough, I’ll probably desolder everything, clean it up, and use some thermal epoxy. It won’t be as good as the solder, probably, but it should be a very thin layer, so hopefully the thermal transfer will still be pretty good.

Update:

I reheated the assembly and adjusted the position of each MCPCB. I checked their positioning using the reflector before moving on to the next one, then one last time before removing the heat and letting the solder cool. It’s pretty good, but most importantly, it’s good enough. Now I have to figure out how to do the electrical hookups.

Amutorch AX1 Quick Look

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I just received a newly-released flashlight from Banggood. It’s called the AX1 and it’s made by Amutorch.

It has a thoughtful, attractive design, and the overall execution is great. But the example I received has a few flaws that really detract from the experience.

First though, some quick observations:

  • Unusual, attractive, well executed, two-color design.
  • Attractive body form, with thoughtful, unconventional, functional details.
  • Large, 22mm, reflector for a 18650 tube light without significant added exterior bulk.  I measured the outer diameter as 25mm, which is just ~1mm larger than a Convoy s2+. The inner diameter of S2+ reflector, though is ~17mm, 5mm smaller than the AX1s. As another point of reference, the Zanflare F1 has an ~20mm reflector, while the OD of the bezel is about 27mm, and the max OD of the whole light is closer to 30mm.
  • Good action on the reverse-clicky switch.
  • Modes seem good. The AX1’s low is pretty close to the low on a Convoy S2+ with an 8×7150 3/5 mode driver. The high/turbo is similar to other ~3A ~1000 lumen lights. There is strobe, but it is pretty well hidden. It has mode memory.
  • The beam pattern is quite nice. Much less floody than a standard S2+ with an XM-L2 emitter and an OP reflector. At 10-15′, the hotspot and spill are much closer to an S2+ I modded with an XP-L HI and a SMO reflector, but the AX1 has nicer smoother, corona with less tint shift, though not as nice as it would be with an OP reflector.
  • I’d call the color temperature neutral white and without an objectionable tint.

Now, for the big problem with the AX6 I received: The surface texture on the blue head and tail pieces is visibly, glaringly, uneven. I had some trouble photographing it, but it is quite apparent when you have the light in hand. When I first saw it, I thought/hoped that it was some surface schmutz. It isn’t, it’s the metal.

Note the machine marks on part of the piece. This is one of multiple areas where the surface texture is inconsistent/in-complete.

It looks like it was supposed to receive some sort of uniform finish, like bead or sand blasting, but some areas were barely touched, so the machining marks are obvious. It doesn’t seem very even over the length of the head either, nor is it consistent around the axis. The problem is most obvious on the head of my light, but the tailcap also has similar but more subtle problems.

In addition, there were a few nicks on the body. The photo above shows the largest of them. These are unfortunate, but the truth is with a weeks use, I probably won’t be able to distinguish them from other wear and tear. The inconsistent finish is going to be obvious for a long, long time.

So, bottom line, this is a nice flashlight for $20-25 if the surface finish is as it should be. Mine isn’t. So I’ll be asking them to replace the faulty parts, if not the whole flashlight.