Electronics in a hot climate

Raveninghorde · 2011-01-13T21:36:35+00:00

I've got an unknown I can't measure.I've got to put some electronics and battery in a sealed yellowplastic box for outdoor use. This piece of kit has to be able to workin direct sun anywhere in the world.So if the air temperature is 50C what is a likely temperature riseinside the box due to sunlight?

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legg 15 years ago

The amount of sunlight reaching a horizontal surface at Earth's surface is called insolation, measured in units of watts per square meter (W/m2).

See pages 18-21 of Bird's "A Simplified Clear Sky Model for Direct and Diffuse Insolation on Horizontal surfaces"

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Around midday on a summer day in temperate climates, roughly 1 kW/m2 of power reaches Earth's surface. About 57% of that is IR (0.7um or greater).

You'd add this burden to the total power being dissipated by your package.

Solar reflectivity, or albedo, is colour and wavelength dependent. Grey will reflect roughly 25% of most wavelengths between 0.4 and

2.2um; white around 75% up to 1.5um, 50% to 2.2um. Yellow?

A go-anywhere package will have a go-anywhere colour. Point that out to 'he who must be obeyed'.

RL

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Greegor 15 years ago

That often alleviates some problems but creates others. Ability to dissipate heat goes WAY down. As somebody else mentioned, moisture in trapped atmosphere can cause problems.

Will the plastic box deform before the pressure release valve releases?

If the battery vents inside of the sealed box, will that vented gas attack stuff it's trapped with?

Failure analysis for this project would be interesting.

Yup.

That could backfire, keeping moist humid air trapped as the temperature drops at night, creating dew inside the box.

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Don Klipstein 15 years ago

Same 75% from .5 um upwards for brighter/lemon/canary yellow, same 75% from .53-.55 um upwards for "school bus yellow" to amber-orange-yellow.

- Don Klipstein (don@misty.com)

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legg 15 years ago

Power spectra is mostly towards the visible end of the IR spectrum - shorter wavelengths. So, worst case 250W/m^2 is collected by a clean yellow box.

Assuming a surface temperature rise of between 0.8 to 1.2 degrees per mW/cm, that looks like a potential additional rise of 20-30degrees on the surface that is directly exposed at noon, if it cannot be redistributed over the entire package surface area. That would depend on box material. Coated with dust, this could double.

Before a first approximation of internal air temperature can be made, you'd need more info on package shape and mounting orientation, box material, wall thickness and internal power loss budget.

RL

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Phil Allison 15 years ago

"Bill Bowden"

No Phil, f*ck off and die is a confusing term. Most people don't know the procedure. The correct term is "Eat S*it and Die" which everybody understands.

** I beg to differ.

The term " FOAD " is well accepted and understood.

In any case, eating s*it is not guaranteed to prove fatal.

Sticking one's head in a microwave oven might prove fatal - if the door interlocks were over-ridden.

So maybe I should try " Go Fry Your Brains F*****ad"

GFYBF does have a bit of a ring to it......

.... Phil

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