So I bought a few of these UV Leds some scorpion hunting.
I should be able to pair them (with their 7.2v vf) with a driver like this and run it with 2x 18650s or 16340s or whatever. As long as I keep the input voltage above the vf of the LED (by half a volt or so), I’ll be golden, right? There is a good chance I’m missing something, so thanks for the double check!
2 18650's in series will have a total voltage ranging from 6V to 8.4V. The regulator needs another 0.9V overhead voltage to stay in regulation. At Vf=7.2, add 0.9 to get 8.1 minimum voltage. The driver will drop out of regulation almost immediately as the battery voltage drops.
You are mentioning only the highest numbers. The ebay-site says Vf of the led is 6.5-7.5V, the driver needs 0.5-0.9V extra. At this current there will not be much voltage loss in the switch or springs, and only minor voltage sag from the batteries . So the driver may not deliver the full 925A all the way, my guess is that the output of the light will be fine for most of the runtime.
Yes, I usually start by looking at the worst case. Best case is a Vf of 6.5 and a driver overhead of .5, meaning you need a minimum of 7V. Two batteries in parallel is 3.5V each meaning it drops out of regulation after the batteries are about half drained. Whether or not that's acceptable is up to you.
First thing I'd do with that LED is measure the voltage and current with a variable power supply and create a plot to see what the line really looks like. Then try it with the driver to see what voltage causes the output to fade.
Also, check that the LED will really fluoresce a scorpion. I've had poor luck with Chinese UV LEDs off eBay. Once an LED listed as 395nm was really around 410nm. Another time it output quite a bit of white light in addition to UV. If this one works well I'd like to know because I have a few scorpion lights in my future (I'm in Phoenix). In the past I've made them with bunches of 5mm LEDs. Bark Scorpions shine nicely at 395nm.
I will certainly let you know. This is my favorite scorp light right now. And it ships from the US warehouse. I find about 5-10 a week with that one (coupled with some yellow UV glasses). I just want to build something more powerful/more ridiculous because I enjoy fighting with my wife or something.
Around 10 years ago I made 2 scorpion lights using Serpac boxes, so they look like remotes (the M6 and A20). One had 12 5mm UV LEDs and 10 white so I could toggle UV/White with a switch. The advantage of a box like this is I'm not constrained to a small round flashlight driver. It opens up a lot of possibilities. The disadvantage is heat dissipation. So I'm thinking of mounting a heatsink on front, with three 700mA emitters (one white) with TIR lenses.
Well, I burnt out the UV LED. I tested the driver over a range of input voltages and it seemed to output a constant .95 amps. I hooked it up to the LED outside of a host and it worked fine. I didn’t do any long term tests (a dumb thing, I admit). But when I put it all together, the LED burnt up. It looks like a couple of the dies in the LED failed. I think each of the little dies inside the LED take around 3.5V and 350ma, and they’re arranged in a 2s2p configuration giving around 7v 700mah. I put 950ma across it and it burnt up. Whoops.
Here is where I confess my ignorance and ask a question: The driver says it can drive 1-4 LEDs. Is that in series or parallel? I assumed it was in series because otherwise “Accepts 3.6~16V input voltage, needs to be 0.5~0.9V higher than total LED VF” wouldn’t make much sense. But if it is in series, how does the driver “know” to output the correct voltage?
Anyway, I’m going to try a different approach. I ordered some UV LEDs with a regular Vf so it won’t be such a pain to drive. Maybe I’ll make a multi-emitter light. Anyone know if I can fit a 17mm driver in a 3t6? I could drive 3 LEDs in parallel with drivers I have laying around.
I’ll try to explain your question. You are correct on the series placement. When an LED driver is constant current, it will try to maintain that current by varying the required voltage to match the emitters’. So when mentioned as 1-4 LED - that would be LED in series. Let’s say one emitter needs 3.5V, two in series needs 7V, therefore 4 of such LED will need 14V and already reaching the limit of the driver.
As you can see, the mention of the LED qty is just an estimation, if you know exactly what Vf you need you can run as many as you can (example you have a red emitter with a low 2V Vf, theoretically you can run 7 of these with 16V input).
For your next buy, yes, I think smaller Vf will make things easier - you can just use 7135s in parallel as driver.
Anyway, I’m going to try a different approach. I ordered some UV LEDs with a regular Vf so it won’t be such a pain to drive. Maybe I’ll make a multi-emitter light. Anyone know if I can fit a 17mm driver in a 3t6? I could drive 3 LEDs in parallel with drivers I have laying around.
Great spirit of determination! I'm currently working on multi-emitter UV too. I purchased 5 3watt 365nm emitters, but I'm thinking of just going with 3. If I go 5, I may get 2 higher frequency emitters to broaden the spectrum.
I don't remember the driver size for the 3t6. I think it is 23mm in diameter. If you have it, you could use the stock driver. 4.5 amps is too high though. So you would want to resistor mod to bring down the current. It is set up for parallel. You can modify a 17mm driver to fit by soldering copper wire or copper braid around the parameter.