Electronics in a hot climate

[Raveninghorde]

I've got an unknown I can't measure.

I've got to put some electronics and battery in a sealed yellow
plastic box for outdoor use. This piece of kit has to be able to work
in direct sun anywhere in the world.

So if the air temperature is 50C what is a likely temperature rise
inside the box due to sunlight?

 

[Raveninghorde]

Completely insufficient data to answer the question... there are
*multiple* unknowns that you have not characterized:

- Actual spectral behavior of the yellow box, and whether it *must*
remain yellow or could be painted a different color.

Thanks for the response.

Yellow is specified by the customer

- Power dissipation of whatever is inside the box.

Minimal, less than 0.25W

- Thickness of the box walls, and their thermal resistance (e.g.
degrees C per watt).

5mm, 0.2" walls. The material is PBT with glass fibre, 30% from
memory. I'll have to set up a test to measure thermal resistance.

 

[Phil Allison]

"Raveninghorde"

I've got an unknown I can't measure.

** Sure you can.

I've got to put some electronics and battery in a sealed yellow
plastic box for outdoor use. This piece of kit has to be able to work
in direct sun anywhere in the world.

So if the air temperature is 50C what is a likely temperature rise
inside the box due to sunlight?

** The temperature of the surface of the box facing the sun is the highest
and unlikely to exceed 70C in direct sunlight. At around 70C, the rate of
heat absorption by the surface become equal to the art of re-radiation by
that same surface. The colour of the surface matters too - black being the
worst case. The outside air will also have a cooling effect on the box.

Take 70C as the worst case the electronics have to survive, long term.

The battery is gonna be your downfall - many of them will not take that
sort of temperature without suffering deterioration or damage.

Better start looking for cell technologies that feature high storage temps
in the specs.



...... Phil

 

[Joerg]

I've got an unknown I can't measure.

I've got to put some electronics and battery in a sealed yellow
plastic box for outdoor use. This piece of kit has to be able to work
in direct sun anywhere in the world.

So if the air temperature is 50C what is a likely temperature rise
inside the box due to sunlight?

Mechanical and aerospace guys are usually quite good at simulating this.
But whatever you do, personally I would not use electrolytics in there.
Even the 105C and 125C types would not be happy campers.

At to "anywhere in the world": If that includes places like Alaska you
need to also consider ultra-low temperatures. For example, crystals can
become like molasses when the temps go to -30C or below. Oscillators
might squarely refuse to start oscillating. And the sun ain't gonna
shine much of the time up there.

Then there's weather. Golf ball sized hail stones, ice pieces flying
about, chunks of trees hitting the box. And in Iceland you might hear a
gigantic *PHOOMP* upon which the box goes flying, along with a chunk of
mountain, lava, smoke, ash, but I guess you can get an exemption from
that

 

[Phil Allison]

"Joerg"

Mechanical and aerospace guys are usually quite good at simulating this.
But whatever you do, personally I would not use electrolytics in there.
Even the 105C and 125C types would not be happy campers.

** How does this bullshitting wanker imagine ordinary electros have been
working inside tube amplifiers and tube TV sets for the last 70 odd years
??

The ambients in some cases are over 90C.


..... Phil

 

[Martin Riddle]

I've got an unknown I can't measure.

I've got to put some electronics and battery in a sealed yellow
plastic box for outdoor use. This piece of kit has to be able to work
in direct sun anywhere in the world.

So if the air temperature is 50C what is a likely temperature rise
inside the box due to sunlight?

Capacitors have an awful temperature coefficient. Make sure your
compensate for that.

Cheers

 

[Phil Allison]

"Martin Riddle"

Capacitors have an awful temperature coefficient.

** One should avoid emotional terms like "awful" when discussing
electronics.

Only a few cap type have poor tempcos - notably electros and high K
ceramics.

Most poly caps are likely to remain within +/-1 % within the range of 0 -
60 C.

Make sure your compensate for that.

** Not necessary at all in the vast majority of cases - like coupling,
decoupling and PSU filtering. Electros actually work better when hot as
their ESR goes down by several times.

Polystyrene caps have the best tempco and polypropylene types have a small,
negative tempco.



...... Phil

 

[Raveninghorde]

Don't forget mist blowing in any vents,
sub-zero temperatures or
blowing snow sandblasting effects.

Vents or no vents?
100% humidity?
Damned if you do, damned if you don't.

It is a sealed unit pressure tested for 1 metre immersion.

Hot, cold and humidity can be tested in a chamber.

On one project I tested abrasion in a gravel filled cement mixer.

 

[Raveninghorde]

Mechanical and aerospace guys are usually quite good at simulating this.
But whatever you do, personally I would not use electrolytics in there.
Even the 105C and 125C types would not be happy campers.

At to "anywhere in the world": If that includes places like Alaska you
need to also consider ultra-low temperatures. For example, crystals can
become like molasses when the temps go to -30C or below. Oscillators
might squarely refuse to start oscillating. And the sun ain't gonna
shine much of the time up there.

Then there's weather. Golf ball sized hail stones, ice pieces flying
about, chunks of trees hitting the box. And in Iceland you might hear a
gigantic *PHOOMP* upon which the box goes flying, along with a chunk of
mountain, lava, smoke, ash, but I guess you can get an exemption from
that

No aluminium elctrolytics. There are 2 tants. The MCU is specified to
-40C with internal oscillator and I can test that.

Hot and cold I can test in a chamber. Solar irradiation is not as
easy.

 

[Raveninghorde]

"Raveninghorde"

** Sure you can.



** The temperature of the surface of the box facing the sun is the highest
and unlikely to exceed 70C in direct sunlight. At around 70C, the rate of
heat absorption by the surface become equal to the art of re-radiation by
that same surface. The colour of the surface matters too - black being the
worst case. The outside air will also have a cooling effect on the box.

Take 70C as the worst case the electronics have to survive, long term.

The battery is gonna be your downfall - many of them will not take that
sort of temperature without suffering deterioration or damage.

The battery is my main concern.

Competitors seem to be using lithium polymer but they are only
specified up to about 60C.

 

[Martin Brown]

Yellow is probably close enough to black as far as longwave thermal
radiation is concerned so I wouldn't worry about the visible colour too
much. White would be better still.

Do you have any control of the shape of the box or its physical design?

A second skin designed to take the suns direct heat and lose some of it
by convection might keep things from getting too hot. As Phil said it
isn't likely to get much above 70C in direct sun but that is bad for
batteries.

ISTR that after ~55C thermal radiation losses begin to dominate over
passive convective cooling so that rate of the temperature climb slows
after that.

An outer shell with ribs or fins designed to be self shading (think
cactus body) and/or with an insulator behind it covered in foil will
significantly slow down ingress of solar heating. A Stephenson screen
used in meteorology for air temperatures gives you a rough idea.

If the internal power consumption is small you might be able to buy
enough time by lining the box interior with the stuff sold for putting
behind radiators (ie foil backed polystyrene foil facing inwards).

The battery is my main concern.

Competitors seem to be using lithium polymer but they are only
specified up to about 60C.

You might be able to limit the enclosure temperature rise over the
typical daytime to something like 10C above ambient. Do you have the
option of having a passive heat shunt inside? Some of the most
aggressive challenging hot sunny climates also have cold desert nights.

Regards,
Martin Brown

 

[Uwe Hercksen]

It is a sealed unit pressure tested for 1 metre immersion.

Hot, cold and humidity can be tested in a chamber.

On one project I tested abrasion in a gravel filled cement mixer.

Hello,

But it should be filled with dry nitrogen before sealing to prevent
condensation.

Bye

 

[Joerg]

"Martin Riddle"


** One should avoid emotional terms ...

ROFL!

 

[[email protected]]

In very cold conditions, the blowing snow can create some nasty static
electricity build up.

Or cover the went with some suitable material letting the air pressure
stabilize, put preventing water from penetrating.

It is a sealed unit pressure tested for 1 metre immersion.

That is only 1.1 bar.

How would that device survive a transport in a non pressurized cargo
bay at 10000 m ? Would it explode due to the internal 1 bar pressure ?

 

[Raveninghorde]

In very cold conditions, the blowing snow can create some nasty static
electricity build up.
Understood.


Or cover the went with some suitable material letting the air pressure
stabilize, put preventing water from penetrating.


That is only 1.1 bar.

How would that device survive a transport in a non pressurized cargo
bay at 10000 m ? Would it explode due to the internal 1 bar pressure ?

I have a pressure release valve. I never fit a battery in a sealed
unit without a pressure release valve.

 

[Phil Allison]

"Joerg is a Snipping **** "

ROFL!

** Wot a fuckwit jerk off.



..... Phil

 

[legg]

I've got an unknown I can't measure.

I've got to put some electronics and battery in a sealed yellow
plastic box for outdoor use. This piece of kit has to be able to work
in direct sun anywhere in the world.

So if the air temperature is 50C what is a likely temperature rise
inside the box due to sunlight?

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"

http://rredc.nrel.gov/solar/pubs/PDFs/TR-642-761.pdf

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

 

[TheGlimmerMan]

What the matter Archie?

Phil and I both should get together, and hunt your retarded ass down,
so that we can then facilitate making the world a better place by our
being here, and you NOT being here any more.

That is what we *should* do.

 

[Don Klipstein]

"Joerg"


** How does this bullshitting wanker imagine ordinary electros have been
working inside tube amplifiers and tube TV sets for the last 70 odd years
??

The ambients in some cases are over 90C.

90 C or more is in local hot spots or in "some cases", not general
ambient in those devices. For general ambient inside, figure more like
25-30 degrees C warmer than outside even in TVs consuming 200-300-+ watts,
even less in high power tube amps that put their main heat-makers outside
what encloses most of their components.

Were there TV sets 70 years ago? It appears to me that we did not have
TV in 1941.

 

[Don Klipstein]

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"

http://rredc.nrel.gov/solar/pubs/PDFs/TR-642-761.pdf

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?

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.