I posted about a quad build I did in the what did you mod today thread a few weeks back, but the recent discussion of CCT mixing in a SST-20 thread made me think it worth a new thread.
I’ve been interested in doing something similar to JasonWW’s Supfire L5 XHP70.2 Mod since I first read about it. I acquired a host back in the spring, but I didn’t get any further because I decided I didn’t want to mess with 2x26350s. I initially thought a boost driver would do the trick, but the combined expense of driver + emitter combined with driver power limits + limited choice of e-switch boost drivers and the prospect of new boost drivers from Mtn, Lexel, etc made it hard to pull the trigger.
While I was waiting, I started to wonder if there were higher-power 3v emitters. The SST-90 was an option, though an expensive one. Someone here had modded a (failed?) XHP50 or 70 to be a 3v emitter, which sounded great, if only it was available off-the-shelf. Then I learned about the Luxeon MZ, and that it was available in a 3v version, and high-cri to boot. Problem solved, right? Nope! I hesitated again, I think to wait for Led4Power to start offering higher-binned versions than what was already available in Q1.
And then I stumbled across these odd-ball MCPCB’s on AliExpress: 20mm, DTP, with four footprints for 3535 emitters arranged in a 2x2 array. The first listing I found was only available in 2s2p and 4s configurations, but I later stumbled across some 3v/4p variants. I knew the beam would be problematic with four widely spaced dies, but the MCPCBs were $1/each, and one already populated with XP-G2s was less than $5. I ordered some.
When they arrived, I put the pre-populated one into a dissapointing host. The beam was predictably bad, but promising. I tried stippling the smooth plastic reflector with a mist of clear spray laquer. It definitely helped, but the beam still had an unacceptable dark spot in the center. I figured I needed a better reflector, but didn’t want to waste money on the crummy host, so I set it aside.
A week or two later, still itching to do a compact, inexpensive, high-output light-build I started thinking about the emitter array again. I remembered that I had a OP C8 reflector, as well as a Thorfire C8s acquired for cheap that wasn’t getting much use. I reamed out the reflector, opened up a centering ring to fit the array, and built the light with a FET driver. The results, sadly, were little better than my earlier experiment, but, having come this far, I decided it was worth trying DC Fix. It did the trick! The light formed an even (very floody) beam after ~3-4 inches.
While I had the light apart at some point, I tried holding the stock reflector in place, and found that it too produced a good beam paired with DC fix, so I reamed it out and used it instead.
I was pretty happy with the light, but in the meantime, I’d begun to appreciate high-CRI emitters more, and I’d managed to accumulate a number of LH351’s that were calling out for a quad build. So, I made a solder paste stencil, and reflowed four of them onto one of the MCPCBs. I prefered the tint of the 4000K emitters I had, but I also didn’t want to run through my stock of them too quickly, so I decided to pair two of them with two of the 5000K variety.
The results were great. Looking into the lens, I could distinguish the two different CCTs, but in actual use they blended into a nice neutral high-CRI flood beam, and a rather bright one at that. With spring bypasses and 18AWG driver leads, I’m able to get ~18A on a fully charged 30Q.
Since then, I’ve done another quick build with some cheap 4000K 80+ CRI XP-G3s and a host with a slightly smaller reflector. The DCFix takes care of the XP-G3s ugly/messy beam.
A final build note, the MCPCBs don’t have “solder steelers”, or whatever they are called to help deal with any excess solder, so its more important not to overdo the solder paste than it is with other MCPCBs.
tl;dr
I tried a number of experiments with some unusual quad-3535 MCPCBs. You might be interested in the results:
The MCPCBs have inherent problems, but they can be overcome with DCFix if a floody beam is acceptable. The upsides are that they are inexpensive, enable high-output 3v lights without requiring a specialized host, or major mods beyond opening up the reflector opening, and provide a ready platform for color-mixing.
Links:
- Blog Post
- AliExpress listing for MCPCB. Note, I actually purchased the MCPCBs from HotRed OTLED Store by special request. They only list the 6v & 12v configurations, but they happily filled my request. I wanted to order from them because they’d provided good service and quick shipping on earlier orders.
Update: Some beamshots:
Left: ~4’ from surface. Right: ~8” from surface.
Surfaces are different shades of off-white, so colors aren’t comparable between shots, but they should give an idea of color uniformity at each distance.