Heatsink design....

[Tim Carleton]

I've noticed the heatsinks I've bought were relatively thin across the diameter other than the led post, is this to wick away heat? Would a thicker heatsink store heat rather than conduct it away?

 

[Tim Carleton]

I'll add that I'm having trouble with some dswoi p-7s from amilite overheating, I'm dd'ing them with 3 nimh d cells. I built a heatsink before and used it in a csxoi and no problems on that one, this one I left thicker, not as much off the back....


and can also add that the thing was getting heat to the outside of the maglight pretty quick, but like it was just drawing more current or something.... I pulled the batts out of my csxoi driven mag.

 

[DocD]

Hi,
take a read of this http://www.candlepowerforums.com/vb/showthread.php?t=214712
and i hope gives you something you can use cheers DocD

 

[Tim Carleton]

I checked my amps this morning, it starts off cold at 2.8 amps on 3/4 charged d's (nimh) and after about 30 seconds the amps start to climb... I shut it down at 3.2 amps. So more mass/less mass across the diameter does not have anything to do with wicking heat away from the led?:shrug:

 

[Tim Carleton]

well I unsoldered the leads from the led, put it back into the lathe and trimmed some more off of the rear under the led, it definitely helped, It's not overheating now, so I answered my own question and I hope this helps someone else who is thinking more mass is necessarily better on a heat sink.

 

[Oznog]

Thermal mass is of little use. I mean if you had an 8oz block of aluminum inside the flashlight with no way to get the heat out, it would take awhile to heat up but it'll still be hot. Well in theory if you had a block so huge it wouldn't heat up before the batteries ran down that would help, except no practical size of aluminum has a mass that would resist heating up for more than a few minutes when heated with 1W-5W.

Aluminum must be thick enough to conduct heat to the fins/case external cooling surfaces with minimal resistance. While the calcs are complicated, conducting heat over short distances with 1/16" thick aluminum is probably more than adequate. The edge of the sink has to make good contact with the case and that requires a thicker edge to increase contact surface. The center may require screw mounts and that requires a certain thickness to hold the threads and not distort under the pressure of the screws.

Copper is a superior material, nearly twice the thermal conductivity of aluminum. It's softer and somewhat more limited in minimal thickness due to mechanical stiffness. It's solderable which is really excellent for some emitters.

Anyhow most flashlight designs have no problem getting the needed thickness and trying to shave the sink just slightly thinner may have no practical benefit, since it might only gain a mm for all the trouble and questions.

 

[Tim Carleton]

Thanks for the thoughts Oz.. this was my first trouble with making heatsinks, and I admit I've been making them progressively heavier, but the tolerance to the case in all have been very snug, they will push in snugly, yet come out by wedging a knife blade on the lip and prying upwards. I use very little thermal grease as most of it pushes out the top and to the bottom of the sink anyways.