Nice demo video but please be aware that thermal images of unpainted
metallic parts can be misleading. A perfect mirror-like surface would
actually show the temperature of the surroundings, not its own temperature.
A real typical clean metal surface will show a weighted average of its
surroundings and its own temperature, with the contribution from its own
temperature being about 30% of what a perfect blackbody would radiate at
the same temperature. A tarnished or oxidized metal surface can have an
emissivity which is much closer to ideal, typically 60 to 80%. However, it
is best to always use an organic material when measuring temperature
thermographically because almost all organic materials are within 10% of a
true blackbody so you don't have to worry about calibrating the camera for
your particular surface.

To make a long story short, the leads of a resistor will usually appear
cooler than they really are in a thermal image.

On Tue, Jan 23, 2018 at 4:55 PM, Forrest Christian (List Account) <
lists@packetflux.com> wrote:

> Since this thread seems to be still alive, I'll add my $0.02:
>
> The degrees rise figure is the typically body temperature, not the
> temperature of the leads at the board, which be much cooler.     Note tha=
t
> on page 10 of the datasheet you linked it shows recommended lead
> termination bending, effectively offseting the resistor off of the board =
by
> 8mm.   I was trying to find a good thermal camera picture to show this, t=
he
> closest was at https://www.youtube.com/watch?v=3D-e-qIjttIIY&t=3D134s , a=
t
> 1:57
> in, there is a thermal camera pic which shows the leads basically being
> cold, while the resistor body itself being hot.   I wouldn't be surprised
> to find that when mounted as recommended, the units will not desolder fro=
m
> the board.
>
> Personally I try to run things as cool as possible, if I was engineering
> for 5W dissipation, I would use at minimum a 7.5W if not a 10W resistor.
> Unless I was *very* sure of the engineering.
>
> Also, be mindful that the rating is at 40*C ambient *around the resistor*=
..
>  If you don't provide adequate airflow around the resistor to eliminate a
> thermal air hotspot around the resistor, you're actually going to have an
> even lower rating.
>
>
>
>
--=20
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