Trying to understand simple LED circuit for emitter swap

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Cheezman88
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Trying to understand simple LED circuit for emitter swap

Hey all, as the title suggest, i’m trying to understand if what i’m doing is okay. I bought this flashlight on Amazon (link below), with the intention of upgrading the LED emitter. I took it apart and it looks like it’s running to 2x R680 resistors in series. I’m wondering if I can swap the emitter to a Luminous SST-40 N5 and have it work with the existing circuit? I’m using a Sanyo ncr18650ga 18650 li-ion battery in the light. Trying to wrap my head around how to calculate if this would work, i’ve been looking at resistor calculators and the spec sheet for the SST-40 but not really understanding it. Thanks

Flashlight: https://www.amazon.com/GearLight-TAC-Tactical-Flashlight-PACK/dp/B07VNCWZBF/ref=sr_1_13?dchild=1&keywords=gearlight&qid=1596075439&sr=8-13

New emitter: https://www.aliexpress.com/item/4000037561899.html?spm=2114.12010612.814...

toddcshoe
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I don’t have one of those particular lights but I imagine it has some sort of horrible emitter already in it. Which isn’t a bad thing. The bad thing is most likely that the board the emitter is on most likely sits on a shelf with nothing but a hollow void underneath it until you get to the driver press fit into place. So it most likely doesn’t deal with heat well. That board the emitter is on is also most likely aluminum. Not worth trying to reuse. So you have to find a board that will fit on the shelf and takes a 5050 led. Be careful about trying to get that thing pumping out the lumens. It will deal with heat in a spectacular and quite smelly fashion.

So yes, you can use the SST40 and yes you can use the existing circuit. The question is, should you. Depends on how much you like that Gearlight. Smile

"Everywhere I go, there I am"

Cheezman88
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Wow, you’re spot on lol. That’s exactly how it is on the inside. I’m not too familiar with emitter heatsink design, i’m assuming this is a terrible design? Well, I guess more for my own reference. How exactly do I read the specs for the emitter? There’s generally a range of Vf. Do I use the highest number of the range to calculate the resistor? How do I figure out the maximum current it can safely handle? And how would I figure out how much current the emitter will actually see in this type of circuit? Does it depend on the internal losses/resistance of the circuit and how much the battery can supply, and not something you could calculate without actually testing it?

toddcshoe
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Well I won’t overwhelm you with all the details. You will get yourself so caught up trying to redesign a 5 dollar light with $40 worth of components. I will tell you what I did to a very similar light. I found a emitter already on a board I knew I would like. Pick the tint and cri of the emitter. Doesn’t even have to be the SST40, I used a SST20 and had very good results. Both emitters will easily handle the kind of current you can expect from this thing. Trying to keep it under one amp or so unless you do some work on the thermal path. Once you got your board and emitter, get the driver out and see how big it is. Then we can find you a driver to size down a little to fit back in there. I’ve used Convoy Biscotti drivers in those with great success. A 2 or 3 chop driver will run that LED just great. I would also give you a bunch of different mode programming options for you. You could also fill in all that dead space with some thermal compound once you get everything working. It will help with the heat a little bit.

Honestly, if you are going as far as ditching the emitter we’d be better off changing that driver as well.

Are you in the US? If so message me your address and I will throw some parts, emitters, boards, drivers, etc. your way.

Let me go root through the parts boxes.

"Everywhere I go, there I am"

Cheezman88
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Dang, I may just have to forgo this project haha. I was hoping it’d be an easy swap. Although I could learn something or two going through with it. I’m not even sure how to get the board out. It looks like it’s either soldered in there or welded or something. And there’s no easy direct access to it because the head doesn’t come off. And taking off the bezel doesn’t get you close enough.

toddcshoe
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When you get the bezel off does the lens come out with it and is there a press fit ring, plastic or metal, before the LED board? If so you should be able to unscrew or pry out that ring. That should allow you to remove the slide portion of the body. Removal of the LED board should allow you access to the driver board. That driver is probably just pressure fit in place. A little pressing or prying around should get it loose. Then it’s just a process of finding or making new components fit. Again, I don’t have that exact light but I have some similar zoomies that work in a similar fashion. If you are needing a good zoomy that doesn’t really need any messing with I may have one sitting around here you can have. Think I have a true 1000 lumen XPL 18650 one I don’t use anymore. You’d have a good working one while you mess around with that Gearlight.

"Everywhere I go, there I am"

Cheezman88
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I’ll have to do some tinkering. The part im stuck on it just removing the board. Thank you for the offer, you’re super kind to offer a stranger on the internet something like that. But i’ll just stick with this for now hehe, I do have a few other lights around.