Already on an MCPCB. I just squashed it down into the thermal paste left after removing the original MCPCB and emitter, I didn’t screw it down. Which would explain why it died in a fraction of a second of full blast.
Having had a little practice reflowing that FET, now I’m thinking I’m probably able to reflow my own LED’s now.
Not a skill I was planning on acquiring but I guess it will be useful … haha. I’m an idiot.
Oh, so you didn’t have any pressure pushing the mcpcb onto the flashlight shelf. Yeah, it won’t last long like that. Normally the reflector/centering ring presses it down nice and uniform around the led.
The screws are for anti-rotation. They might work decent for heat transfer, but I wouldn’t trust full power to them. Not with a FET driver and a 70.2.
Over heating explains the 2nd led going bad. I wonder why the first one went bad? Maybe it’s reflow onto the mcpcb was not so good. The middle pad of the xhp70/70.2 is just for heat transfer. If they didn’t have enough solder there it may not have transferred the heat quick enough.
Reflowing the emitter is not too hard. You just need something to hold the mcpcb while you blow the hot air up from the bottom. I hold the hot air gun between my legs and hold the mcpcb with some pliers. I raise and lower the mcpcb to change the temperature. My free hand can use tweezers to remove the led.
Then I use my solder iron to remove the old solder and apply new solder. Then you heat it up again over a minute or two with the new led sitting on top of the solder and a dab of extra flux. This will preheat the new led slowly avoiding thermal shock. Once the solder goes liquid I make sure it’s centered and push it down so any excess solder comes out the sides. Then remove from heat and let it solidify.
It can happen with any LED I think, I have seen it with several brands and models thus far.
Not sure on the exact cause but I am guessing the LED just fries itself internally and after that the internal “resistance” is such that only a small amount of light can be made. I have noticed the Vf increases drastically on LED’s that have this issue.
Isn’t cutter in AU? I think you could get a replacement LED form them that is better then what lumintop uses much easier. They have good prices as well if you live in AU and don’t have to pay the shipping.
But then we wouldn’t have had this wonderful adventure together now would we?
I tried looking for an au seller for an led but came up with nothing particularly good. I just ordered a couple more from mntnelectronics. And I asked lumintop if I could have another on an mcpcb just incase I bugger it up with the reflow…… covering all bases. Already spent silly $ why stop now…
Great! Thanks!
Did you have trouble opening the head? I haven’t tried yet…
Are 8 cells recommended or does it work the same on 4? - i’ve got a choice of 35E (actually in my GT) or 30Qs… I’m assuming 4 is enough to power a single 70.2?
The head was kinda tight, not too bad. I used a rubber strap oil filter remover tool to unscrew the head.
On 4 cell’s 30Qs are recommended due to high amp draw (for high power-on lumens) Should work fine, but lower runtimes obviously.
On 8 cells 35Es will be fine.
I removed the switch cover so I could clamp it in a vise. Pieces of wood with a depression for the switch will also work. I found that loosening the upper head from the lower head removes tension on the bezel rubber seal which makes the bezel a bit easier to unscrew.
I had to use a lot of force and slowly unscrew the pieces. They are tight.
@Jason: Thanks for the picts - i think i saw them somewhere some while ago… Damn, it does not look easy. I would have to get the rubber tools and a bigger vise… Not sure i’ll get into this mod.
How about heating the bezel wish a hair drier? It should dilate a little more then the head and become easier to unscrew? That may damage the lens though?
I clamped the flattened part with the button on it in a work-mate. Unscrewed the whole top including reflector with a simple rubber strap shown in JasonWW’s pictures. I didn’t really need the tool I think. Mine came loose easily, so I guess there is a lot of variation.
