Ventilation for the Bela + BBB

papa_sangre

Hi all - happy new year!

I'm mounting the Bela in a plastic box (a tupperware, about 20x10x10 cm), which will be stored in a larger metal flight case (about 100x50x30cm).

The Bela will run a program while stored within these two cases (the plastic box nested within the flight case).

Audio and signal cables will be fed out of the flight case through tightly insulated holes. The entire setup is intended for outdoor use, and must be protected from water damage.

In other words - with the current setup, the Bela is not getting any ventilation while in use. The board will be powered by an RS 5200mAh battery, and will be running for about 2-3 hours at a time

My question is: How necessary is ventilation for the Bela? Do you think it would be sufficient to ventilate the inner plastic box (for instance with air holes, or a small 3cm ventilating fan)? Or must the outer flight case also be ventilated?

I don't want to make any more adaptations unless they're 100% necessary!

Thank you again for your help 🙂

giuliomoro

I think it should be fine to just have ventilation holes in the tupperware. The board absorbs about 2.5W.

Leave it running for a while and then check the temperature and make sure it's safe. I would use a termocouple (which these days comes with many digital multimeters) to measure the temperature of the surface of the big chip on the beaglebone

ryjobil

Is the inside of the flight case metal, or is it lined with something? If you have a decent amount of inside air exposed to the metal then the flight case won't get very hot inside.

A really easy non-technical experiment would be to put the Bela + BBB in the tupperware and leave it powered for a couple hours. Come back and touch the tupperware.

If the tupperware is only warm to touch, it's probably ok. You can take it a step further by taking it out of the tupperware and immediately stick your finger on the top of the CPU on the BBB. If it's uncomfortably hot, then you should poke some holes in the tupperware. If you can hold your finger on the CPU without discomfort you have nothing to worry about and you can leave it all sealed off.

Just making sure the tupperware box has good contact with metal in the flight case could make a notable difference. Another thing could be to wrap the tupperware box with aluminum foil with a crumpled outer surface (maximum surface area to air in the flight case. These are simple things that don't require making holes.

Ultimately this is a thermal conductivity and heat capacity consideration. If thermal conductivity was, say, 20C/Watt, then the air inside the tupperware would eventually end up at about 50C higher than the surrounding (outdoor) air temperature. This would be ok, but not good for long-term reliability.

Heat capacity consideration defines how much time it takes for the BBB to reach the final temperature. For example, it may have the 20C/Watt thermal resistance, but it might take 3 hours to get there, so operating for 3 hours at a time this would not be a problem since most of the 3 hours would not be very hot.

Finally, outdoor temperature will make a difference. It might be ok when it is 20C outside, but is it ok when it is 35C outside or if it is exposed to direct sunlight?

You can keep sheltered from direct sunlight, but if you operate it on a hot day, you should take it out at the end of the event and stick your finger on the CPU to see how hot it gets.

A thermocouple is more scientific, but you will know it is operating at a safe temperature as long as it isn't uncomfortable to touch the CPU.

papa_sangre

Thank you both for the advice - this is immeasurably helpful. I'll report back once I've run a few tests on the completed prototype.