Heat problems - Ideas?

[ausbump]

I'm building an LED drop in for a very old torch - but i've encountered a problem. Having just engineered the switch & the head exactly the way i wanted them - and being very happy at the output - i now have heat problems.

Here's the emitter mounted on a small (too small) heatsink:

The emitter is a P4:
http://www.dealextreme.com/details.dx/sku.3475

The barrel of the flashlight is 3.5 cm (1.5 inch) wide.

Any ideas? It gets too hot to hold after 30 seconds of operation - and i have no doubt it would burn out if i kept using it.

 

[alphazeta]

What current are you running through the led?
What's the material of the light you're dropping that into? metal? plastic? :shrug:

I'm sure you catch my drift.
We'll need a little more 411.

 

[ausbump]

What current are you running through the led?
What's the material of the light you're dropping that into? metal? plastic? :shrug:

I'm sure you catch my drift.
We'll need a little more 411.

I believe it's 800mA at 3.7V. But that's the DX specs so i wouldn't believe it too much

The light is metal, but 'old aluminium'. It's corrugated along the length of the light, so nearly impossible to sit something flush with.

 

[havand]

Wow, too hot to handle in 30 seconds?! That's crazy. I guess better heatsinking to body...or more aluminum. If you could do both, the better.If it isn't a sealed light, you could put a very small computer fan on there.

 

[richdsu]

If you use Cree Q4 or Q5 Emitter ( having lower internal resistance) instead of P4 Emitter , it will not generate so much heat at 800mA.


:naughty:

 

[legtu]

you can...
-reduce current
-increase the heatsink size/mass
-find a way for the heatsink to transfer heat into the flashlight body

 

[alphazeta]

I think the current is way too high for that tiny heatsink. I have a Q2 cree running off a USB cable @ just 0.4 ~ 0.5 amps attached to a 3" x 3" x 3" finned copper cpu heatsink & even that gets very hot (in about 2minutes) with just passive heatsinking.

I think your best bet is to really find a way to upgrade the thermal contact to the body. Otherwise, I just don't see it turning out well.
At 350ma or below most crees won't generate much heat at all. However, I'm not sure you would happy with the output. But yes, pumping down the current would be the easiest way to solve your heat problem.

 

[diff_lock2]

If the heat sink is getting hot then the thermal contact should be ok. the only solution is pump less power or use a bigger heatsink.

I had the same prob. i over volted (over amped) a led cause im dumb, and the whole heat sink got super hot. turned it off took 30sec to cool down.

 

[ausbump]

Right.
Is it likely that a CPU heatsink will have enough heat dissipation capacity to passively cool a cree?
I'll try taking down the power, but i don't anticipate much of a change.

Open to more suggestions

 

[havand]

Right.
Is it likely that a CPU heatsink will have enough heat dissipation capacity to passively cool a cree?
I'll try taking down the power, but i don't anticipate much of a change.

Open to more suggestions

Like I said, if the body of the flashlight is metal, you could try to make the heatsink transfer the heat to the body (and ultimately the air and your hand).