Mail Archives: geda-user/2020/01/15/16:11:49
Hello Nick,
Op 15-01-20 om 18:28 schreef Nick Bowler (nbowler AT draconx DOT ca) [via
geda-user AT delorie DOT com]:
> On 1/15/20, Richard Rasker (rasker AT linetec DOT nl) [via
> geda-user AT delorie DOT com] <geda-user AT delorie DOT com> wrote:
>> [snip]
>>
>> Still, I wonder what the approximate current capacity of these thermals
>> is? I know from experience that a few amps is no problem at all, but I'm
>> pretty certain that they'll fail upwards of 25A or so. If possible, I
>> prefer thermals for easier soldering, so a more accurate estimate of the
>> limits would be appreciated.
> Resistivity of copper ρ is about 1.7 × 10^-8 ohm*m at 20°C, with
> temperature coefficient α about 3.9 × 10^-3 / °C.
> [snip calculations]
>
> 25A: each thermal will dissipate 20mW or 80mW altogether.
> 50A: each thermal will dissipate 80mW or 0.3W altogether.
> 100A: each thermal will dissipate 0.3W or 1.2W altogether.
This is about as far as I got too...
> How hot the thermals will get is a system design question of
> how well you are heatsinking that generated heat away. They are
> presumably connected to a large copper plane which will help.
And this is the main problem. Even a few dozen milliwatts can be too
much if the heat isn't conducted away as fast as it's generated. But
indeed we're talking about a large copper plane, so the heat can spread
out pretty fast -- and I never actually experienced anything below 100
mW giving problems in any way.
Based on the numbers so far, I'd say that 25A isn't a problem at all,
but 100A will probably cause trouble, and pretty fast, at that. And I'll
also have to look at inrush current (two terminal blocks connect to a
pretty beefy 1 kVA SMPS).
OK, thanks, it seems that these thermals are more resilient than I
thought, and 16A should not be a problem at all.
Best regards,
Richard
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