So, my friend is making an escape room for her brother's birthday. I offered to make a prop for her: a skull with UV lights in the eyes that lights up when placed on a base with a hidden magnet.
I've been flying by the seat of my pants so far, but it's gone fairly well, aside from a couple of mistakes (which are what I come to you for help with).
Basically, I modified a skull 3d model to accommodate the pill and lens from some super-cheap 18650 flashlights (I believe they're sometimes referred to as 'battery holders') from Amazon. That part went well. The print, that is:
Anyway, I gutted two of the flashlights (huge pain. Clearly not intended to be disassembled that way. A hacksaw was involved) and replaced the LEDs with 365nm LEDs I got on Aliexpress (probably mistake #2 at least). Overall, it mostly works as expected. The problem is that the LEDs keep shifting color/wavelength after very little use. I've replaced each of them a couple of times already, and they seem okay at first, but then get whiter/yellower, even without much use.
My strong suspicion is that this is caused by a combination of poor-quality LEDs and effectively no heat dissipation from the hollow aluminum pill taken from the donor flashlights causing them to overheat (there might also be a voltage issue, since I neglected to check the voltage being output by the donor light boards, and the UV LEDs are rated 3.2v-3.6v).
Anyway, I'd appreciate some suggestions on relatively inexpensive "good enough" donors and replacement LEDs. I also have UV pass filters for each eye, but don't currently have them in, as they basically block all of the light since the LEDs aren't putting out 365nm anymore.
(Also, would it help if I actually soldered the edges of the star UV LED boards to the aluminum pill? I can't imagine that would transfer enough heat, but … shrug)
Thanks!
(if you saw this just a second ago, I deleted and am reposting with a title that sucks less)
by rootyb
1 Comment
What you describe does sound a thermal issue (unless the zoomie lens is made of plastic which absorbs a lot of UV!), but sadly I don’t think there is a good solution.
The problem with your LEDs is not that they’re from Aliexpress; it’s that they have (1) no thermal pad and therefore a very poor thermal path, and (2) a very tiny emitting surface, which pushes up power density and causes localized overheating. If there’s still time, I would re-order some 3535 or 5050 LEDs, reflowed on a MCPCB that has a dedicated thermal pad. The LEDs themselves should resemble these:
https://preview.redd.it/0stx1x4inpmg1.png?width=291&format=png&auto=webp&s=aef252032d7ce6482973a12c9dc1abbc8abb1027
To improve heatsinking once you have better LEDs, get some thermal paste; even pasting the LED boards to a stack of coins (or any flat metallic object) is better than nothing at all, which is what the hollow pill offers. If you have the money, you can get some Convoy S2+ type lights as donors.
BTW, you can’t solder to aluminum. The oxide layer of aluminum is very tough and won’t let the solder/flux get through.