Hi! So this is getting frustrating! I put an xhp70.2 as an upgrade in my s70, and it has been working great now for a couple weeks. Then all of a sudden today it just died when putting on turbo, completely burned out. I have a resistor bypass done so the I was getting around 7 amps at the tail. Led was reflowed on the stock maxtoch board by heating it with a torch, tested and all worked fine and has now for weeks. The board has mx4 thermal paste and is screwed in place as stock. What am I doing wrong here? These leds should be able to handle alot apparantly, or is 7 amps too much? Normally I use the light on mode 2 or 3 between 3-5 amps. Really confused here. What are your thoughts ? I really seem to have bad luck with leds. I bought the xhp70.2 led from lht flashlightstore on aliexpress.
7 Amps should be a joke for the XHP70.2, it can handle a lot more.
During reflow, did you squeeze the emitter into place to ensure that the excess solder is pushed out of the sides?
Not doing that might have caused the emitter not to a direct thermal connection with the pill.
Other than that, you might have gotten a defective emitter.
No I just let it heat up and flow in place, didn't press it. The funny thing is the led worked fine for weeks haha. I wonder if lht flashlightstore(kaidomain of aliexpress) sell real leds? Are they legit? the real thing you think?
I am not sure if not pressing the LED during reflow could result in such bad result but that’s always a possibility.
I haven’t seen any counterfeit XHP70.2 emitters. The only factor that they could scam you on is the actual binning of the emitter.
I bought the xhp70.2 from an other seller before, and those leds were fake burned right up haha, it was from shenzhen ot led, they were half price of the real xhp70.2 too haha. Lht store seems legit to me but don't know.
Here’s why you have to tap them for best solder joint to pcb :+1:
Reflowing XHP70 too fast result in a premature death,
thermal shock is not good, a good reflow with heating up and cooling down should take a few minutes, Cree specifies 1.2K per second above 170dCelsius
ok, is it ok to use regular solder instead of paste?
You think heating with a mini torch is too much? What do you suggest? A small hotplate?
So reflowing badly could cause premature failure? But why did it work for a few weeks fine?
Could I reflow using a cloth iron? Do I need solder paste or can I melt solder on to the board first?
paste or solder wire makes no difference, just make sure enough is below the LED and it bounces, then give the LED a tap to push out too much solder
if you use a small torch that’s OK, but you need to add some mass to heat up slowly like a small plate of aluminum 7x7cm 6mm thick turned out OK for me before I bought a temperature controlled heat plate
best also check temperature with an IR thermometer, so you see how fast temperature is rising and you don’t overheat the LED
how about torch directly under board ? That's what I did. How about using a cloths iron?
A method to kill or badly damage the XHP70 LED in 100% of the cases
The thermal stress on this big LED is way too much if you heat the star with a torch
If you heat the LED up slowly to 200dC within 2-3 minutes and let it cool down slowly the same time, this wont hurt the LED
And never put a cold LED on a hot star
Never tried a cloth iron. I made a heatblock from two heating-elements made for 3D-printers, and a block of aluminium (link).
You can melt some common solder on the board, but you will have to pre-tin the led as well, or at least put flux on the pads. Using solder paste makes life way easier though…
I use a hot reflow station. Initially, I thought the expense would be a waste. After reflowing my first LED I was sold! It literally takes seconds. 100% temperature control (you can use a lot less heat with hot air) and you just add enough flux and paste.
edit: you can also pre-tin with an iron and then use hot air/flux. I recommend Louis Rossmann and similar youtube channels. They do this kind of work every day and their techniques can be helpful.
Yeah, I've seen those too, might be on my list to buy aswell...
7A at 6v or 12v?
If it was at 12v then no wonder it burned up, you need a proper CPU heatsink with fan to cool that.
A Thorfire S70 uses 2 - 26650’s
6v, yeah 12v would be insane at 7amps haha.
yes i know, I use liitokala 26650's