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I am trying to understand the heatsink datasheet provided in the following link:

https://www.fischerelektronik.de/web_fischer/en_GB/PR/SK434_/datasheet.xhtml?branch=heatsinks

My problem is that the heatsink is available for lengths:

50 mm / 75 mm / 100 mm / 1000 mm

I am trying to find the thermal resistance for the 1000mm one. From the graph you can see that the thermal resistance is only given on the interval from 40-200mm. How can I find the thermal resistance for 1000mm?

Thermal resistance plotted against length of heatsink

If anyone know I would really appreciate the help:)

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  • \$\begingroup\$ 1000mm is quite a large heatsink, are you sure? Maybe you're meant to cut it up into smaller sections. \$\endgroup\$
    – user253751
    Oct 16, 2020 at 11:07
  • \$\begingroup\$ Yeah, I am not going to use the 1000mm heatsink I am currently designing a PFC and trying to minimize the volume of the PFC. Therefore, I have made a program that takes a given switching frequency then calculates the total volume, I just want to visualize the drastic change in volume that happens when the frequency is high. \$\endgroup\$
    – FluidProblem
    Oct 16, 2020 at 11:25
  • \$\begingroup\$ If it doesn't have to be entirely accurate then I would approximate it as a reciprocal function (some number divided by the length). A 1000mm section is just 5 200mm sections in parallel. (In reality that's not true because the heat has to travel farther which adds extra thermal resistance) \$\endgroup\$
    – user253751
    Oct 16, 2020 at 11:27
  • \$\begingroup\$ Thats a good idea, thank you! \$\endgroup\$
    – FluidProblem
    Oct 16, 2020 at 11:31
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    \$\begingroup\$ They don't expect you to use a 1000mm heatsink : they supply it in 1m lengths so you can cut it into N pieces of any length you want. \$\endgroup\$
    – user16324
    Oct 16, 2020 at 12:19

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Curve fitting your data led to this answer. However it might very well be possible that extrapolating the data like this is not a good way to find out what the thermal resistance is at 1000mm. For further reference, here is the data gathered from elsenaju:

Curve Fitting Data

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