LED burning?

[MrNaz]

I have recently modified a Princeton Tec Miniwave LED to replace the existing emitters with 3 x SSC P4 emitters. In the process I removed the existing low quality wiring and replaced it with short lengths of the inner strands of a CAT5 cable. I then simply de-soldered the old emitters and replaced them. The result works, but one of the new LEDs is turning blue after a few seconds of burn time. I turn it off soon after, as I suspect this is happening due to overheating of the pill. Is this just a heat sink mating problem, or does this suggest voltage/current issues? As far as I can tell, they are all being direct driven from 4C batteries in series, thus delivering 4.8V

Am I on the right track here, or am I being a total noob? This is my first attempted mod, the emitters arrived from DX yesterday and I bought my first soldering iron and multimeter from the shop this afternoon.

 

[datiLED]

If you have one SSC emitter turning blue, while the others do not, it is related to the LED not being well sinked. You may have an air bubble under the LED, or it is nor glued down. Remove that LED and clean the epoxy, and reseat it. Also watch out for the LED's base, as it is tied to the anode.

There is no way that an SSC P4 could be direct driven from 4.8V. There must be resistors, or a buck circuit.

 

[MrNaz]

You are correct, there are resistors. Would I be better off replacing this with something more sophisticated? Getting a regulated output would be great, if that's possible.

What is a good thermal compound to use? I have arctic silver from my work on PCs, but I would like to confirm that it is suitable for use on LED pills. Is this OK?

 

[yellow]

arctic is a thermal glue, when You come from the PC-world, You should be used to use thermal paste (because it is much better in getting heat away)
... do this to the led as well!

as datiled has mentionned, the one Seoul will not be placed good.
If You got them on a Star: there have been some incidents a few time ago, where the Seouls were mounted with even an air gap between slug and Star.
Check for it.

 

[smflorkey]

I have arctic silver from my work on PCs, but I would like to confirm that it is suitable for use on LED pills. Is this OK?

Arctic Silver is a great heat transfer compound. You probably want the adhesive version to attach bare P4 emitters to your Miniwave.

If you have P4 stars which you screw to your Miniwave you could use Arctic Silver or Arctic Alumina thermal compound (heat sink grease) so the stars could be replaced later. Well, technically, you can remove stars that you glued down, but the 'thermal compound' is a lot easier.

Hope that helps,
Steve

 

[saabluster]

arctic is a thermal glue, when You come from the PC-world, You should be used to use thermal paste (because it is much better in getting heat away)
... do this to the led as well!

as datiled has mentionned, the one Seoul will not be placed good.
If You got them on a Star: there have been some incidents a few time ago, where the Seouls were mounted with even an air gap between slug and Star.
Check for it.

Arctic is a brand. They have several types of both adhesives and compounds.