Heatsink thermal resistance

[Sceadwian]

Can anyone hazzard a guess as to the heatsink to ambient thermal resistance of a heatsink like this little guy? I have a bunch similar to it, some slightly larger, I'm looking for a ball park estimate.

Without information on the heatsinks I've recovered any tips anyone can give on how to estimate thermal resistance would be appreciated.

I'm sure it's better than the case to ambient of 80 C/W but would like to get a +/- 5-10 degree estimate.

 

[JimB]

Similar to these:

https://www.electro-tech-online.com/custompdfs/2012/05/0900766b80077715.pdf

About 7°C/W at an inspired guess.

JimB

 

[bountyhunter]

Can anyone hazzard a guess as to the heatsink to ambient thermal resistance of a heatsink like this little guy? I have a bunch similar to it, some slightly larger, I'm looking for a ball park estimate.

Without information on the heatsinks I've recovered any tips anyone can give on how to estimate thermal resistance would be appreciated.

It's easy to measure using a TO-220 diode attached to the sink. Measure the diode drop at room temp then let it heat up with a known current through it and forward voltage (to calculate the power) then measure the VBE hot and calculate temp rise estimating 2mV change per degree C.

 

[Sceadwian]

Thanks for the empirical testing info bountyhunter ironically this is for a constant current driver, so after I build this I may be able to do what what you suggest =) JimB's info seems to be just what I was looking for as far as a ballpark for thermal resistance. Just trying not to blatantly fry the thing from over current with low resistance loads when I test it after build (a version of it has already been breadboard successfully up to 1amp)

Every time I ask a question like this I kick myself for buying the thermal gun I have, which is a 1 inch port that has a 1:9 spot ratio. As I found a close focus one (.1 inch spot at 1 inch) which is what I actually need to quickly thermally monitor things like this.

 

[Sceadwian]

Jim, based on the PDF you just posted being so close to what I have, I think 10 C/W is closer. Gives me about 7-8watts of dissipation, and that's on the safe side.

 

[rumpfy]

Go online and have a look in RS Australia. <www.rsaustralia.com>. In their catalog they have hundreds of heatsinks for which the thermal resistance is given. They are an international company based in the UK. Element14 is another company.