# Just killed another sst-90...



## Fichtenelch (Aug 18, 2010)

Hi,
just wired up a d2flex in a 3C Mag with an sst-90 on a britelumens heatsink. attached the sst-90 with some 2-compound heatsink glue (which was intended for computers and never did a bad job yet (except on the 1.st sst-90 that died the same way)...
It was pretty bright, but started to smoke...turned blue, i switched it off...

now, what would you guys do? I'm a bit fed up of sst's and i want an ssr now, since the wiring below the led needs to be thick for max current and thin to not interfer with the heatsink....i think i'll just file it down and glue a ssr-90 on it...good idea? And any cheap sources for a good ssr + intl shipping/shipping in germany?

Thanks


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## Fichtenelch (Aug 18, 2010)

Does anyone know if the SST-90 fits on a cree-star?


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## DM51 (Aug 18, 2010)

I think this will do better in the LED (emitters) section. I'll move it there for you.


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## HarryN (Aug 18, 2010)

Hi, I can understand your frustration. I have a long history of consuming LEDs during development myself. At least the price of LEDs is relatively low now days vs 7-8 years ago.

The blue color is an indication that the drive current was a tad high. Keep in mind you are trying to run a 30 or so watt LED here, and the "on time" of such an LED will tend to be short in a hand held light or it will overheat.

Perhaps you can help us understand a bit more of your setup? What cells are you running? I am guessing that they were not C size NiMH.

The D2Flex is an excellent driver, but it is not a current limiter. The concept of that driver is that it turns "on and off" very fast. It is up to the end user to make sure that the "peak" on current is less than the LED max, which does not seem to be the case here or it would not have turned blue.


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## Fichtenelch (Aug 18, 2010)

I think that overheating was the problem, lets say it like that. it was not turning very blue (like my 1.st sst 90)...
and yes, i drive it with 3xni-mh, 3500 mAh stated capacity.
I asked the guys from taskled if they think that i should limit the current and they told me, that i propably have enough internal resistance...so, i think i'll try with an ssr...

The led is not completely dead, a small piece of it, maybe 1x1mm is still illuminating and also switching modes. (i haven't figured out completely how i configure my d2flex, since the led only worked for max. 3 minutes with 2:20 of it switched off.....


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## pepko (Aug 18, 2010)

))

sst-90 has no problem with 12-15A current ... I use 4x AA nimh direct drive here :
https://www.candlepowerforums.com/threads/280018

I think that your heatsink or thermal path is very very bad ...


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## Fichtenelch (Aug 18, 2010)

I think i'm going to grind down the heatsink and glue+screw a ssr-90 on it...


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## nailbender (Aug 18, 2010)

Hi 

I have used many of britelumens heat sinks both P7 and SST 50 & 90 and one thing I have learned is use good quality heat sink epoxy and use very little of it. 

I remember a member that burned several p7 leds up and when he used less no more problems.

I have had problems with a couple of 90's and those heat sinks and when I re-mounted with very thin films of epoxy I had no problem. you need to make sure the led is firmly seated all the way down, if even slightly above edge compound is too thick. Make sure the wires allow for led to seat down. I do coat wires and total bottom surface but very thinly.
I myself have better luck with AA than AS but that is me. 

As for Cree boards they will fit but not well, they are best on Luminus boards which are some of the best MCPCB's I have used. 
The SST 50 fits Cree boards perfectly.


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## Curt R (Aug 18, 2010)

At Peak we solder a brass 8-32 screw directly to the heat pad on the SST-50/90 LED. The circuit board that 
the screw passes through is for electrical contact only. The LED assembly is then screwed into the the 
heat sink using thermal paste and then stacked in place. Thermal transfer is very important with any 
high power LED, and this will also include the new Cree XM-L with it's very small pad. A similar approach 
may be required to drive it at 2.5 Amps. 

Curt


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## Fichtenelch (Aug 18, 2010)

nailbender said:


> As for Cree boards they will fit but not well, they are best on Luminus boards which are some of the best MCPCB's I have used.
> The SST 50 fits Cree boards perfectly.




Are there stars for SST-90 available somewhere?

Thanks


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## nailbender (Aug 18, 2010)

Fichtenelch said:


> Are there stars for SST-90 available somewhere?
> 
> Thanks




Hi 

Avnet has them listed with the SST 90's. When you run a search on SST 90 tick the *in stock box* and they will be on the first page. 

Fred in market place usually stocks 90's on boards and may have some boards only but don't know for sure. 

Dave


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## MikeAusC (Aug 18, 2010)

The Thermal Resistance of even the best thermal compound is MANY TIMES higher than a metal to metal path.

The area under the SST90 is still very small, and if you don't do a perfect job, there will be a very high temperature rise.

I've been doing fine electronics soldering for fortyfive years, but I still decided to get an SSR90 ( a mounted SST90 ) because of the strict conditions to get reliability from soldering an LED - read the data sheet !


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## moviles (Aug 19, 2010)

I prefer the sst-90 with star and good screws
photonfanatic have the stars at 3.5$

I have buy 3 stars


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