SST-90 smokes?

[Eddie-M]

Hey, I just built my SST-90 mag flashlight. I am running it through der wichtels 9A buck driver.

With fresh batteries, a thin trail of smoke exits around the emmiter. On dead(ish) batteries, there is no smoke. I have not noticed a shift in color to the blue side when it happens, it only takes a few seconds, then I turn it off out of fear.

Is it possible the heat from the LED is just burning away extra solder flux left over on the wires soldered to the LED? I used arctic silver epoxy to glue it to the heatsink, any chance the epoxy might smoke a bit until it cures, I only glued the emmiter a couple hours ago but the glue sets in like 10 minutes.

I don't want to my SST-90, speaking of which, do they just burn out or do they make a noise too, like a "pop" or something?

Thanks

 

[Eddie-M]

I just read the other thread about that guys SST-90 turning blue. I compared the color of mine vs a SSC P7 and mine is blueish off the bat even though I bought 5700K neutral tint bin. I'm going to try to remove and redo the mount, I think my layer of arctic silver is too thick. As for the smoke, no idea, it smells like soldering though.

 

[350xfire]

No noise they just stop working... I've burned up 3 of them and about 4 Ostars! Plus countless P7, MCE and XRE! Boy, this hobby is expensive!

 

[Eddie-M]

No noise they just stop working... I've burned up 3 of them and about 4 Ostars! Plus countless P7, MCE and XRE! Boy, this hobby is expensive!

Thats good. I'm not a fan of things that go bang; baloons, champagne bottles, ect

Update: Remounted the SST-90 and left it clamped. OK, this time Its a much thinner layer, one side wasn't seated all the way upon examining the left over paste after prying off the emitter.

 

[Eddie-M]

Success, no more smoke, and the tint went from blueish to more yellow than my ssc-p7

Still don't know where the heck the smoke was comming from lol

 

[irv_usc]

probably your LED got so hot it was cooking the dome.

 

[Eddie-M]

probably your LED got so hot it was cooking the dome.

Do you think I caused permanent damage? I can run the LED for long periods now, no smoke, no tint shift, I run it until I feel the maglite is getting too warm in my grip. I don't like that thought that I cooked the dome

 

[Aircraft800]

Why Arctic Silver? Arctic Silver Compound is very slightly capacitive and could potentially cause problems if it bridges two close-proximity electrical paths.

A better choice would be Arctic Alumina Adhesive, it's a pure electrical insulator, neither electrically conductive nor capacitive.

 

[saabluster]

Do you think I caused permanent damage? I can run the LED for long periods now, no smoke, no tint shift, I run it until I feel the maglite is getting too warm in my grip. I don't like that thought that I cooked the dome

I imagine things will be fine from here on out. You were probably cooking the epoxy. I'm sure that's where the smoke was coming from. Good thing is you learned a valuable lesson without having to lose an emitter in the process.

 

[CKOD]

Why Arctic Silver? Arctic Silver Compound is very slightly capacitive and could potentially cause problems if it bridges two close-proximity electrical paths.

A better choice would be Arctic Alumina Adhesive, it's a pure electrical insulator, neither electrically conductive nor capacitive.

No, arctic silver should never be a problem on power LED. Slight capacitance shouldnt be a problem at all, as you can already add an unknown slight capacitance with your leads running to the LED. What they are addressing is when people use ASTA for video cards or attaching RAM heatsinks. When you have a whole line of parallel traces running at 900MHz + feeding some ram chips, capaitance matters, when you have a impedance controlled differential PCI-Express trace running at 5 Ghz and a few hundred mV, then capacitance matters. When you have DC power to a device consuming somewhere between 1-35 watts, a few stray pF or nF (what you would likely see from the ASTA) dont matter, a few uF should generally be safe, with excess capacitance (tens of uF plus) possibly causing stability issues if the driver wasnt meant to handle that capacitance on the output.

However, I would avoid using it on driver boards, as there, you do have high impedance high frequency singals being passed around, and adding capacitance to a feedback trace would change the feedback circuit and possbily cause instability.

Slather it on the leds, dont be afraid :naughty:

 

[ma_sha1]

Why Arctic Silver? Arctic Silver Compound is very slightly capacitive and could potentially cause problems if it bridges two close-proximity electrical paths.

A better choice would be Arctic Alumina Adhesive, it's a pure electrical insulator, neither electrically conductive nor capacitive.

For bare heat sink, may be. But for Anodized heat sink where no worries of conducting electricity, Arctic Silver has almost 2x better than Arctic Alumina on heat transfer, assume same thickness of the glue layer were used.

Arctic Silver thermal conductivity is >7.5 W/mK.
Arctic Alumina is rated at >4 W/mK.

Unless one is directly soldering led to the heat sink (solder is in the 30-40 W/mK range depends on brands), the Arctic Silver is as good as it gets within reasonable price range.

 

[Eddie-M]

I imagine things will be fine from here on out. You were probably cooking the epoxy. I'm sure that's where the smoke was coming from. Good thing is you learned a valuable lesson without having to lose an emitter in the process.

Lesson learned. By epoxy, did you mean the epoxy I used to glue the emmiter, or whatever epoxy holds the dome onto the sst-90? Thanks.

No, arctic silver should never be a problem on power LED. Slight capacitance shouldnt be a problem at all, as you can already add an unknown slight capacitance with your leads running to the LED. What they are addressing is when people use ASTA for video cards or attaching RAM heatsinks. When you have a whole line of parallel traces running at 900MHz + feeding some ram chips, capaitance matters, when you have a impedance controlled differential PCI-Express trace running at 5 Ghz and a few hundred mV, then capacitance matters. When you have DC power to a device consuming somewhere between 1-35 watts, a few stray pF or nF (what you would likely see from the ASTA) dont matter, a few uF should generally be safe, with excess capacitance (tens of uF plus) possibly causing stability issues if the driver wasnt meant to handle that capacitance on the output.

However, I would avoid using it on driver boards, as there, you do have high impedance high frequency singals being passed around, and adding capacitance to a feedback trace would change the feedback circuit and possbily cause instability.

Slather it on the leds, dont be afraid :naughty:

I wasn't too worried about arctic silvers capacitance when glueing the LED. I did however use 3 carefull drops around the perimeter of the driver to hold in the heatsink. I placed it on parts of the board where there were no electric connections. I kept them well away from any solder points ect.

 

[saabluster]

Lesson learned. By epoxy, did you mean the epoxy I used to glue the emmiter, or whatever epoxy holds the dome onto the sst-90? Thanks.

The silicone used to hold the dome will not smoke unless it got far hotter than is even possible with that LED. I was referring to the epoxy you used. All that heat was dumping into that layer of epoxy but had nowhere to go since it could not transmit it fast enough to matter with it being as thick as it was.

 

[Eddie-M]

The silicone used to hold the dome will not smoke unless it got far hotter than is even possible with that LED. I was referring to the epoxy you used. All that heat was dumping into that layer of epoxy but had nowhere to go since it could not transmit it fast enough to matter with it being as thick as it was.

Ah, that makes sense. Thank you for the info!