amatbrewer
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RPI cooling while sealed in a plastic case...

Wed Dec 07, 2016 10:57 pm

I am looking for ideas/suggestions.
Note: I have been searching around the forum for ideas and while there are plenty of discussions on cooling, I could find none that were very relevant to my question. I will apologize in advance if I missed finding where this has already been discussed.

I have built a RPI3 based controller for a small greenhouse. In the summer the air temperatures will often exceed 100F (it can be over 120F). There is no place to put the device that it will not be exposed to at least some spray from the irrigation (it is a very small greenhouse) and being in a greenhouse the humidity tends to be quite high most of the time. The Pi along with a power supply, relay and AC outlet are enclosed in a plastic case (about 8”X5”X3”) with minimal openings. My fear is that it will overheat during the summer months and I am thinking about ways to cool it. I would like to avoid moving air in/out as much as possible to protect the device from the high humidity. I would also like to avoid using a different enclosure if I can. And since it is linked to my network via the on board WiFi, a metal box is out of the question.

FYI I have harvested the heatsink/fan from an old graphics board. One idea I have considered is to cut away part of the box and cover the opening with the heatsink. I am just not sure how effective that would be without some method of getting the air inside the box moving. There is also not that much surface area on that side of the heatsink, and there is not enough room inside the box to mount the heatsink/fan inside. I have also already considered a peltier heat pump, but based on the expense, complexity, and relatively high power usage, I have mostly ruled it out as an option.

Has anyone encountered this and if so come up with any good solutions?

ElEscalador
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Elescalador

Wed Dec 07, 2016 11:39 pm

Not what you asked, but sounds like a good application for a pi zero that likely wouldn't need any cooling.

I think even the 3 should be ok if you dont minds the cpu throttling when it's warm. Maybe.
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jbeale
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Re: RPI cooling while sealed in a plastic case...

Thu Dec 08, 2016 12:18 am

> And since it is linked to my network via the on board WiFi, a metal box is out of the question.

Or not. There is a case (mostly aluminum, with plastic bottom lid plus cosmetic / optional top lid) that has almost no effect on the wifi. I have one of them, they weren't too expensive, about $14 each. The case has a metal protrusion that reaches down to contact the SOC and also has an adhesive thermal pad to make good thermal contact, so the whole metal portion acts as a heatsink. It is this item: Flirc Raspberry Pi 3, 2 and B+ Case https://www.amazon.com/gp/product/B00QB6F9I0

Another comment: your case temperature doesn't have to use the air ambient as the heatsink. Wouldn't the ground (soil) be cooler on average than 120 F? Seems like a hollow concrete block sitting on (or partly sunk into) the ground could maintain a cooler climate for your R-Pi.

amatbrewer
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Re: RPI cooling while sealed in a plastic case...

Thu Dec 08, 2016 4:50 am

Thanks for the suggestions.

I have been looking for an excuse to get a Pi Zero but not sure why it would be better able to handle the heat. Can you elaborate?

Using earth to help regulate the temperature is interesting, but since the greenhouse has a concrete floor, it would be difficult to do.

ElEscalador
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Elescalador

Thu Dec 08, 2016 3:00 pm

120 is not too hot on it's own. The zero will add much less than a 2 or 3 would and it so low power it may just stay under the 80deg C throttling threshhold. The wifi adapter may add more heat than the zero...but I'd still try it - no matter what it'll need much less cooling across the barrier that is the case.
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alphanumeric
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Re: RPI cooling while sealed in a plastic case...

Mon Dec 12, 2016 1:54 pm

Why not mount the enclosure on the outside of the green house, then run a cable inside to the sensors etc? Then put something above it to deflect any rain way and keep direct sunlight off of it. If you keep the rain from hitting it you can then put vent holes in the bottom to let some air in and some of the heat out.

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HawaiianPi
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Re: RPI cooling while sealed in a plastic case...

Thu Dec 15, 2016 7:51 pm

There are a couple of different ideas that come to mind.

The first would be to use a metal block or dowel large enough to cover the CPU and stick out of the case slightly. Use a good thermal epoxy to bond it to the CPU and silicone RTV to seal the opening in the case around the block or dowel. The purpose if this is to move heat out of the case, so copper would be good because it conducts heat very well. Then you attached a large heatsink to the outside end of the block or dowel, something with a lot of surface area so that you won't need a fan. Aluminum would work well for that because it radiates heat better than copper. Use thermal epoxy to bond the heatsink to the block/dowel.

Another option would be to use a heat-pipe type cooler. Some desktop computer, and many laptop coolers use heat-pipes to quickly move the heat away from the CPU to a heatsink located elsewhere. These can be extremely effective, but they are not something you could easily make yourself, so you would have to find an existing one that would fit your needs. Sealing the case around the heat-pipes could also prove challenging.

Suggestions above about using a Pi-Zero are also worth considering. If the software you are running doesn't require the power of a Pi3, a Zero will generate less heat. Of course it also only has a single USB port (which would be used for a WiFi dongle).
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omegaman477
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Re: RPI cooling while sealed in a plastic case...

Tue Feb 28, 2017 2:51 pm

I do a lot of harsh environment work, and over heating is always an issue. Ideas..

1. Potting the RPI in a heat conductive silicone is often very effective, use a solid aluminium case with external fins as the pot. But this is a one way trip. Some silicones a pickable.

2. Use an oversized aluminium SEALED case, and install a small internal fan. Back to back mount fin style heat sinks to the internal and external case. The fan prevents hotspots, and heat will always dissipate to the cooler exterior.

3. Peltier cold plates will 'suck' the heat away from the cold side, but will need ample fans and fins on the hot side, they are also power hungry. http://www.ebay.com.au/itm/like/161953068502

4. a lot of liquid cooling systems around for the gamer PC market. Never keen on water in the equipment enclosure.

5. Thermally couple the RPI CPU chip (70% of the heat) to the inside of the metal case with a block of aluminium or copper.
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omegaman477
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Re: RPI cooling while sealed in a plastic case...

Tue Feb 28, 2017 2:56 pm

Interestingly enough the new GreenIQ smart irrigation controller, which is in a swanky plastic case is built on a RPI. Ihave mine in the Aussie summer sun (over 80C on case external) with no issues. But I have a sun shade for it.
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Flypi
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Re: RPI cooling while sealed in a plastic case...

Sun Dec 10, 2017 1:10 pm

I know it's an old thread but i just wanted to add:

How i would fix this:
So from what i understand, you have the RPI in a greenhouse and inside an enclosed box.
I would make a pipe going from the box to ouside of the greenhouse. Then add a fan that sucks air from the outside and blows it trough the RPI and out a second pipe that has a second fan that blows air outside.

That way, you could have cooler air recirculating and blowing hot air out and keeping the RPI much more cooler.
Ofcourse add a filter material to filter out bugs and dirt.

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