Just how much hotter will a black enclosure be?

[DSGarcia]

The problem... the standard enclosure color for a cast aluminum box I want to use (about 4" x 8") only comes in black (or unfinished). Just how much hotter will the inside of the box be when the box is used outdoors? I am using industrial temperature range parts, but am very concerned about heat on a hot summer day. Usually, the box will be in the shade, and perhaps I can see that it is always shaded. Unfortunately, I think sometimes it could be placed in direct sun, but not often. I do need to plan for worst case, but I can try to make sure worst case is in the shade if being in the direct sun is too hot.

The enclosure manufacturer is adding the cutouts and doing the silkscreen. If not for the silkscreen, I could have it powder coat painted. I do like the looks of the black box except for the heat concerns.
Thanks,
Dale

 

[RadioRon]

It seems to me that you could use data from the heatsink industry. They know the relative effectiveness of an aluminum heatsink when black anodized vs not black in the situation where there is no forced air flow (what they call natural convection). I think this relative difference would translate directly to your situation. Unfortunately, in my brief review of online technical info from Aavid-Thermalloy and Wakefield I did not find a number you could use. You should contact one of them to get this number.

 

[justDIY]

black not only absorbs radiation better, it also radiates it better. so provided your black enclosure is not subjected to radiation (you mention shade), then it will radiate internal heat better than virgin or other color enclosure.

 

[DSGarcia]

black not only absorbs radiation better, it also radiates it better. so provided your black enclosure is not subjected to radiation (you mention shade), then it will radiate internal heat better than virgin or other color enclosure.

justDIY,
So you are saying that if there is not direct sunlight on the enclosure, I am in good shape and perhaps even better?

However, I still have the question of in case one were to not pay attention and allow direct sun light to shine on the enclosure, how much of a problem might it be? I do not have control over the users other than explaining the rules.

I'm thinking of just buying a couple of thermometers at the Wal*Mart and leaving it out on a hot sunny day. I presume if the outside air temperature were 90 degrees on the day I do the test, I should add 30 degrees to the result for the hottest day of 120 degrees though one usually would not be out working with the equipment when the temperature was over about 100 degrees.

hmmm... now you have me worried about the sub-freezing winter days. I was hoping the heat from the equipment would keep things warm enough inside.

Thanks,
Dale

 

[justDIY]

what kind of equipment are you working with. if it's temperature sensitive, you could add a thermal cutoff or protection device to cut power should the temp exceed some set point.

if you're using industrial (extended) temperature parts, they should be able to handle working in whatever temperatures you're likely to encounter. some parts are rather limited, a chip I recently ran across is rated for 0 to 85C ... not sure why the lower rating is only 0C, that's not very cold, in my region we're lucky to have temperatures above 0C during winter.

 

[kjennejohn]

Heat is removed by convection or radiation. Most of the heat from your circuitry is collected in the air sorrounding the components, so you have convection cooling. This heated air then has to pass the heat off to the metal to reach the outside world, where it is eliminated by both convection and radiation. The black surface affects the radiation capabilities.

Anyways, if the enclosure doesn't have to be sealed, consider using louvres (cooling slots) and/or attaching large heat devices like the regulator(s) to the case's walls to get rid of heat faster.

'Luck with your project!
kenjj

 

[Hero999]

How much heat does your project give off?

If it barely uses any power and the components are all rated to >100 degrees C then it's unlikely that it will overheat, there again it depends on how hot it is where you live. What's the typical maximum summer temperature?

 

[stevez]

I think your idea to actually test the enclosure is probably best. If you can't install the circuits to be powered in the enclosure you might simulate the heat with a power supply and some resistors.

 

[DSGarcia]

Unfortunately, the enclosure is sealed (to protect against weather and wash-down) so venting is not possible. The main component is a single board computer rated from -20C to +70C (-4F to +158F) so I think I will be alright if I don't get more than a total 40F temperature rise. The computer uses 2.8 watts maximum. I will be using an external power supply so that will be a big help.

I did not want to sink a lot of money into a batch of enclosures without some idea that they were not going to have to be tossed out.
Thanks,
Dale

 

[sam2]

Cant you paint it white?
On a hot summer day, in direct sun ,a black metal box will be almost too hot to touch(with no electronics heat).
Maybe 130 degres, it does not give much room.
If you paint it white, it wont be much above the ambient temperature.
sam

 

[DSGarcia]

Cant you paint it white?
On a hot summer day, in direct sun ,a black metal box will be almost too hot to touch(with no electronics heat).
Maybe 130 degres, it does not give much room.
If you paint it white, it wont be much above the ambient temperature.
sam

Sam2,
Good point, but for custom colors [i.e. other than black], I need to order a minimum of 200 units and normally I will only be ordering perhaps 20 at a time. I could have the boxes powder coat painted myself, but then the vendor will not take the boxes back to be subsequently silk-screened.

So, I only have two choices: the Henry Ford option--get black boxes with the silk screen or the painful option--to get unpainted boxes, ship them to be painted (the nearest vendor is about 50 miles away), then find a silk screen vendor and ship them to be silk-screened (the local vendors only do T-shirts and such)--all of which adds time and expense.

I think I will have to live with the black--I do like the looks. About 98% of the time I have control over making sure the box is installed in the shade--usually in a large metal building. I'll just need to manage the last 2% and hope for the best.

Thanks,
Dale

 

[Frosty_47]

Black metallic objects tend to heat up quite a lot above ambient temperature when exposed to direct sunlight. If I were to build an exterior enclosure, I would wrap it in cotton (old T-shirt should do). That way, your project will still maintain its rug ness while a layer of white cotton around your project should do a good job at repelling sun rays. Oh, and you can also make your "silk-printing" easier by wrapping the your enclosure with the pre-printed cotton.

 

[Frosty_47]

A Good quality wrapping should be as good as a paintjob. And more interesting too…

 

[DSGarcia]

Black metallic objects tend to heat up quite a lot above ambient temperature when exposed to direct sunlight. If I were to build an exterior enclosure, I would wrap it in cotton (old T-shirt should do). That way, your project will still maintain its rug ness while a layer of white cotton around your project should do a good job at repelling sun rays. Oh, and you can also make your "silk-printing" easier by wrapping the your enclosure with the pre-printed cotton.

Sorry Frosty nice try--had me thinking I could silkscreen a T-shirt and wrap up my box. The silkscreen is to label 12 connectors plus company name, etc. There is also a color touch-screen display, two push buttons (including emergency stop), a USB port with snap cover, and mounting hardware (RAM-Mount), keyboard, and speakers.

My best solution when not inside a building is to use shade or if outside on a hot day to just sip on a lemonade instead of working.
Thanks,
Dale

 

[Hero999]

Painting it white might not make any difference as the white paint might still absorb in the infrared range which is what really makes the difference.

You could try bolting a large heat sink to the shady side of the box.

 

[justDIY]

the paint is only but a thin skin, the black box is still underneath, some of the visible light will be reflected by the paint, but most of it will still be absorbed by the box.

white paint on a virgin color box will work better, but that sounds like a lot of trouble. how about searching out another enclosure vendor?

 

[DSGarcia]

Painting it white might not make any difference as the white paint might still absorb in the infrared range which is what really makes the difference.

You could try bolting a large heat sink to the shady side of the box.

Hero,
Thanks for the advice. Unfortunately, with everything there is on the enclosure, there is almost no room at all for heat sinks and no guarantee that the tiny strip that is available will be out of the sun when used outside. Shade is my answer when outdoors in the open (less than 2% of the time and only for part of the year).
Thanks,
Dale

the paint is only but a thin skin, the black box is still underneath, some of the visible light will be reflected by the paint, but most of it will still be absorbed by the box.

white paint on a virgin color box will work better, but that sounds like a lot of trouble. how about searching out another enclosure vendor?

JustDIY,
In this case, the only color available is black (or unpainted) unless I order 200 or more boxes at a time. I have checked enclosure suppliers for Mouser, Newark, and Allied and this is the 'perfect' box other than the color issue. I actually have two boxes (4 counting minature waterproof speakers)--one for the computer and another for the miniature keyboard and they are exactly the same except for the depth. The equipment needs to be compact to stay out of the way of the operator.

I was originally planning on a custom made stainless steel enclosure, but using cast aluminum will save me a couple hundred bucks per system. For the rare instance of an open sunlight installation, I will demand the shade. It is not worth the hassle for such a small percentage of the time this could possibly be a problem. Most installations will be inside a large metal building.
Thanks,
Dale

 

[DSGarcia]

Question: I edited my reply twice and in the "edit" version, miniature is spelled "miniature", but in the post it is "minature". Is this a conspiracy intended to make me look illiterate?
Thanks,
Dale

 

[mneary]

Is your color touch-screen display rated for this kind of temperature?

 

[DSGarcia]

Is your color touch-screen display rated for this kind of temperature?

-20C to +70C