P7 i'll killed another one HELP

[DocD]

ok i burnt up yet one more P7 i have built 23. and 11 regulated 3d mags and never had this problem two DMM to check Forward volts and amps yet the past 3 have burnt up under 30 seconds two have burnt out the neg side of the P7 and the other the pos the only difference is I bins and not j bins.
Also i solder my wires to the P7 without it being attached to a heat sink
i'm at a total loss i don't know what i am now doing wrong can any one shead some light?
cheers DocD

 

[steve6690]

Hi Doc. How are you driving the P7's, and what heatsinking are you using. What you're describing is more than likely to be caused by either too high a voltage or insufficient heatsinking. My testbed bare MC-E overheated recently and I think the problem was caused by using the cheapo DX thermal glue too thickly.

 

[Norm]

I think the problem was caused by using the cheapo DX thermal glue too thickly.

The DX thermal glue isn't suitable for P7s no matter how thinly you apply it, you really do need to use Arctic Alumina epoxy.
Sorry to hear about your problem Doc.
Norm

 

[steve6690]

The DX thermal glue isn't suitable for P7s no matter how thinly you apply it, you really do need to use Arctic Alumina epoxy.
Sorry to hear about your problem Doc.
Norm

Yep, I learnt this the hard way . I have a new MC-E 'M' bin going in a prototype light today....with AA epoxy

 

[DocD]

hi, thanks norm
i,m using AA thermal adhesive or should i be using ceramic type?
How and when do you solder on your wires ? cheers DocD

 

[geek4christ]

I can heartily recommend the AA. In a pinch, you could use Arctic Silver mixed with regular old 5 minute epoxy (like Devcon brand found at Wal-Mart). If you do that just mix equal parts Arctic Silver, Hardener and Resin. It won't conduct heat quite as well as the Arctic Alumina will, though.

It's also a good idea to use the thermal epoxy first, then solder the wires on. That way you don't have the force of the wires tugging up on your epoxy while it cures.

Sorry about your burned emitters.

 

[mudman cj]

Use the ceramic type when you need to electrically isolate the slug from the heat sink. In order to be sure it is isolated, it is best to first apply one very thin layer and let that cure before you mount it with a second thin layer. You can also use the hair trick to mount in one step by placing a hair on either side of the slug (after applying the epoxy) to created a separation between the slug and heat sink when mounted. I try to use the silver epoxy or silver thermal grease with a dab of super glue to hold the emitter in place whenever electrical isolation is not necessary.

 

[DocD]

cheers for the info can any one throw some light on when i should be soldering my wires to the P7 like be for i glue it too the heat sink or after. i,m using flux, clean tips, super HQ solder, and tinning the wire and feet on the led,
i just for the life of me see were i,m going wrong all of a sudden :thinking:

 

[Norm]

I find it easier to solder after mounting the LED, it's not on a star so not too much heat gets dragged away while soldering the legs.

It's also a good idea to use the thermal epoxy first, then solder the wires on. That way you don't have the force of the wires tugging up on your epoxy while it cures.

Norm

 

[yellow]

whatever thermal glue one uses, skip it,
use thermal GREASE when You have to get heat away.

there will be no differenence at all between AA and "some cheap DX thermal glue crap", or simple epoxy adhesive, when all are applied thinly, because all are just epoxy glues.

--> thermal grease for heat,
then screws on star, or epoxy glue around emitter/Star to mount the led
AA is only expensive, nothing else


Other pros except for much less cost and considerably better heat transfer:
the led can be applied in place and stay there semi-glued. But can still be moved, while with glue, are bond after a few mins.


PS: as to the soldering.
a Guess: too much heat for too long time. The contacts heat up and melt out of the emitter.
as has been mentionned: 1st place the led, then use a low power iron (instead of my expensive soldering station which I skipped, I now use a plain 15 W iron. Works much better) and quick soldering.
Maybe heat the contacts 1st and put a small amount of solder on them, same with the wires, then put them together, move iron on them and do the final soldering.