Safe current for unheatsinked Cree?

[AvPD]

Can anyone tell me from experience what currents produce damaging temperatures for a Cree P4 without a heatsink? This datasheet says that 200mA results in 50 degrees centigrade but will this dramatically shorten the life of the LED?

 

[Jarl]

When you say "dramatically shorten" how much does this matter? They're rated for 50,000 hours!

Just bear in mind that the hotter the junction temperature, the less light they output. So, as nonsensical as it sounds, you may be better with a lower drive current where the LED wouldn't warm up so much.

 

[LukeA]

When you say "dramatically shorten" how much does this matter? They're rated for 50,000 hours!

Just bear in mind that the hotter the junction temperature, the less light they output. So, as nonsensical as it sounds, you may be better with a lower drive current where the LED wouldn't warm up so much.

You could shorten the life of the LED to 10 or 20 hours.

 

[mds82]

I just simply wouldn't recommend doing it at all. i had a junk XR-E laying around once, so i ran it at 700ma with no heatsinking and it didnt even last 1 minute.

 

[LukeA]

I just simply wouldn't recommend doing it at all. i had a junk XR-E laying around once, so i ran it at 700ma with no heatsinking and it didnt even last 1 minute.

I'm not even sure what kind of project would call for an unheatsinked emitter.

 

[cdosrun]

I'm not even sure what kind of project would call for an unheatsinked emitter.

I did consider it for my car, my heater control panel had two little tiny incand lamps in that blew and I couldn't find replacements. I threw four Nichia CS 5mms in but that was a couple of years ago and the connection on one of them is not brilliant. I was considering opening up the console again and putting in a couple of XREs at a low current, there doesn't appear to be anywhere to heatsink them to though :-( So, I would be interested in a current that might be 'safe' for a prolonged period, 50-75ma?

Andrew

 

[LukeA]

I did consider it for my car, my heater control panel had two little tiny incand lamps in that blew and I couldn't find replacements. I threw four Nichia CS 5mms in but that was a couple of years ago and the connection on one of them is not brilliant. I was considering opening up the console again and putting in a couple of XREs at a low current, there doesn't appear to be anywhere to heatsink them to though :-( So, I would be interested in a current that might be 'safe' for a prolonged period, 50-75ma?

Andrew

Is they're star-mounted, 50-75mA will be fine.

 

[AvPD]

I'm not even sure what kind of project would call for an unheatsinked emitter.

I replaced the unheatsinked LED of this type in a torch like this one with a Cree P4 mounted on a 16mm base. By experimenting with a multimeter (10A socket, dial set to 10A, removing the tailcap and completing the circuit) I got a reading of between 0.400 and 0.500 on a fresh battery, which I assume corresponds to 400mA-500mA. I had been hoping the circuit board would only deliver between 100-200mA, given the original LED. There's not enough access to do something like thermal glue the board of the LED to the case (and I might want to reuse it), and I'm not sure how effective sticking something to the back of the LED would be.

Yesterday I tried running it (without the head) with various batteries and touching the back of the LED's board after some heat had built up, it didn't get too warm at currents under 250mA, which partially drained batteries provide. Interestingly the heat didn't spread through the whole board (even at 500mA), only the centre directly under the LED got warm.