heat dissipation

I need to put the Diecimilla and an ethernet shield (Freeduino ethernet) into an enclosure (box). I’d like to keep it as compact and simple as possible… It is to be an autonomous data collection device, indoor, but I have little control over the temperature in the “room”.

The box is to have holes for the connectors (USB, power, ethernet, and a stereo headphone). The box is to be as small as possible. (The one I currently have is ~57 mm wide, ~70 mm long and ~ 33 mm high – just enough to accomodate the components; and it is made of plastic (about 1.5 mm thick)).

I estimate the generated heat to be around 0.5W (AVR ~300 mA/5V=~150mW, power regulator (7.5 or 9Vs input) <200 mW, ethernet controller <150 mW).

  • Am I about right in the power consumption estimate?
  • Does any of you have any relevant experience if and how this kind of config can be put in an enclosure with about these attributes?
  • Do you think I can stay with the box as-is, should I simply drill more holes into in, should I install a small fan, or something else?

Oh, yes, and an extra one: Arduino is designed so that shields can only go above the processor board (which – in many cases – is the most power-intensive part). Why is it so? Would it not make sense to have a (perhaps optionally inserted) set of connector pins on the downside? (I see, it is not a problem as long as it is only a development board dangling around the end of pieces of wire on a desk. It may, however, become an issue in cases when it turns into one-of-a-kind production device.)

In the grand schema of things this is a very low power system and I wouldn’t bother taking any precautions. Electronics will normally work quite haply in an ambient of 50 C, most chips are rated to work at 70 C which translates to a junction temperature of 100 C.
Depending on the ambient the box is in it might pay to keep it in the shade as direct sunlight into a sealed plastic box can up the temperature a lot.
The regulators produce the most heat and you can reduce this by feeding them with about 7.5 V rather than 12, the extra power is just burned.
This setup defiantly does not need fans, and at most would need some small vent holes top and bottom.

Thanks a lot.