jrperry
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Enclosure for sub-zero temperature

Sat Oct 05, 2013 5:59 pm

Hello,

I am looking at using a RPi for a year round outdoor application. The only problem is the temperature drops below 0 C in the winter. The average daily low temperature in my area is about -10 C and we have seen temperatures below -20 C even though they are not common.

I am planning on mounting the RPi in a Pelican case and using waterproof fittings for any wires leaving the box. The entire project is going to be run off solar. The only problem is I have no experience with doing outdoor projects. Do I need a heater? If so what kind of heater should I be using? Is mounting it in a Pelican case the right route? are there any issues I need to think about because I am going to have batteries in the enclosure? On the opposite end of the year. Is there anything I need to worry about through the summer? Should I vent it?

Does anyone have resources to help keep a RPi running outside in the winter????
I do not need all the answers to the list of questions I am willing to learn the hard way but I am interested if anyone has resources or knowledge to help me along the way!

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Hove
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Re: Enclosure for sub-zero temperature

Sat Oct 05, 2013 8:24 pm

Low temperature doesn't sound like a problem; high temperature may be, but keeping the case in the shade so the sun can't warm it's innards to 80 degrees is all that's needed - no venting necessary for the RPi itself. You'll need to watch condensing humidity, but as long as your case it closed in low humidity conditions (and assuming this is the same kind of Pelican case that provides full immersion protection I used for my DLSR collection and lenses), then not a problem except for leading wires out of the case - some silicone sealant should solve that. Of course, that's assuming the case stays shut!

Which leaves battery power - many high power batteries (like Lithium variants) don't like the cold, and become inefficient - what kind of batteries is the solar charging? Again, this may well not be a problem as for the solar charging to work, the sun needs to be out, so the inside of the case may well be within the working temperature range of the batteries - I guess you'd want to add a temperature sensor to monitor it to make sure.
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jrperry
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Re: Enclosure for sub-zero temperature

Sat Oct 05, 2013 9:31 pm

I found some info on the FAQ page. The Ethernet module is only rated for use from 0 C to 70 C, but the processor is rated for use from -40 C to 85 C. I may look up the other parts and see what they are rated for. I am not sure how much I will even use the Ethernet connection since it wont be near my wired network. You bring up a good point about the sun warming things up. I was only thinking about the bottom end. I am planning on putting the case up on a pole that is out in the open. I may want to think about finding a way to shade it.

As for the enclosure, yes that is the same case. I am also thinking of using a junction box used for outdoor wiring since it may be cheaper and will still be air and water tight. I am still looking at my options and want to make sure I have thought of as much as possible before I start to build.

I was thinking of using Lithium-ion batteries but have a friend who is into solar so I was going to consult him before I got too far into the project.

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rurwin
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Re: Enclosure for sub-zero temperature

Sat Oct 05, 2013 10:36 pm

You need to make sure the case is airtight, even with different air pressures inside and outside, or you need to drill a small hole in the bottom of the case.

During the day, the air in the case expands. If the case is not airtight, that excess pressure escapes. At night the air in the case contracts. If the case is not airtight, air flows in from outside to equalise the pressure.

That would be OK except for water vapour. In hot weather the air going into the case has a high humidity. Overnight it cools and the water condenses out. Only tiny amounts condense each night, but very frequently, you can open a case after a year, that is supposed to be airtight and water-tight, and find an inch of water inside.

If there is a hole in the bottom of the case, in a place that doesn't allow water to splash, then any accumulated water can drain out. Unless you are actually going to immerse it in water, a small hole in the bottom does not allow rain to get in.

Having a hole might cause more corrosion than having a truly airtight case, but you need to over-engineer that airtight case.

jrperry
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Re: Enclosure for sub-zero temperature

Mon Oct 07, 2013 2:06 pm

Personally I think I would be too concerned about the corrosion: so, I guess I am going to see how air tight I can make the case.

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Lob0426
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Re: Enclosure for sub-zero temperature

Wed Oct 23, 2013 2:43 am

For those low temperatures I would suggest some closed cell foam insulation. Styrofoam or such. With enough insulation, the heat of the RasPi should work until it gets real cold. So get a pelican case that will allow at least three inches (75mm) of insulation, four inches (100mm) would be better.

I think I would use a sealed lead acid battery as long as weight will not be a problem. The battery will act as a thermal mass to help stabilize temperatures. A small incandescent bulb, attached to a thermostat, could be used to add additional heat inside the case in low temperatures.
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karlkiste
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Re: Enclosure for sub-zero temperature

Wed Oct 23, 2013 5:50 am

Lob0426 wrote:I think I would use a sealed lead acid battery as long as weight will not be a problem.
I'd like to point two things out: In summer, the pi might not want to sit behind 4" styrofoam. Heat is a common problem, cold is not. Just put the pi in the deep freeze and see if it keeps working: I bet it will.

About sealed lead acid batteries: They are not as "sealed" as one might think. They have valves, so in certain cases gas (oxygen and hydrogen) can escape the "sealed" battery. Therefore, it's strictly forbidden (and usually printed that way on the battery itself) to charge lead acid batteries in a gas-tight container. Also, lead acid batteries don't like the cold. If discharged, they can even freeze.

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Lob0426
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Re: Enclosure for sub-zero temperature

Wed Oct 23, 2013 6:41 am

Sealed lead acid does not freeze very easily, if kept charged (and he stated he is going to charge them with solar), and it does not put out as much hydrogen, most is reabsorbed at discharge. A vented motorcycle battery would also work, they have a tube for ventilation that could be passed through the box. On the other hand LiPo's lose performance very quickly below about 40F (4C). NiCad or NiMh would be better than the LiPo but not better than the lead acid. Also cost is a consideration. My preference would be a marine deep cycle (Jet ski battery). It would give years of service without any trouble.

The hard foam can be easily removed when warmer weather comes around. Also remember that the RasPi can take high (85C(185F)) temperatures better than low temperatures (-20C (-4F)). So even if you waited until early summer to remove the foam it will still be within its temp range. The foam would also protect the battery from the cold.

At -4F the heat from the RasPi alone plus an inch or so of foam would probably take care of it. When you have low temps and are running off a solar charged battery you do not want that bulb to come on very often or for very long. That is why I would err on the side of too much insulation rather than a little too less.

It often gets to -17C (0F) here (or more) and car batteries never freeze if they are kept charged. I have had to head for work in -20F (-28C) temps and not had starting problems. I have had NiCad batteries refuse to work at 0F.

Mount the RasPi on one piece of the foam with some standoffs, then you only have to remove the foam on the sides and the top for summer.
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Re: Enclosure for sub-zero temperature

Fri Oct 25, 2013 9:59 am

I am planning on mounting the RPi in a Pelican case
It would be a good idea not to take a black model as it will heat more when exposed to the sun.

karlkiste
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Re: Enclosure for sub-zero temperature

Sun Oct 27, 2013 5:40 am

I'm planning to use pis outdoor as well, so I've tried it. After a night in the freezer at -30°C (-22°F), the (uncased) pi started without a problem, network and USB doing well.

Right after booting raspbian, the core temperature reported -20171. After half an hour running under no-load condition, core temperature has stabilized to about -5000.

This makes me very confident, that the pi can be run at low temperatures. Heat can easily permanently damage silicon. Cold can not. Therefore I would first think of how to survive a hot summer day in the sunshine, and wouldn't worry about cold winter nights.

And, I'd definetly prefer risking the pi to temporarily stop working at -40° (C or F) from the case exploding from battery gases, ripping someone's head off.

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ragnarjensen
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Re: Enclosure for sub-zero temperature

Sun Oct 27, 2013 9:58 pm

jrperry wrote: I was thinking of using Lithium-ion batteries but have a friend who is into solar so I was going to consult him before I got too far into the project.
Be aware that you shouldn't charge lithium batteries at temperatures below freezing.
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klevasseur
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Re: Enclosure for sub-zero temperature

Wed Jan 08, 2014 2:28 pm

FYI: I've set up my RasPi in my garage to measure temperatures that have been in the -18C to 0C range for the past 3.5 days. It's been measuring and tweeting temps (@WeatherAt03031) every hour over that period without a problem. I've got it in a simple plastic enclosure, which is in a small cardboard box without insulation. A DS18B20 Digital temperature sensor is sticking outside the garage.

A few days earlier, it got down to -25C at 6AM and I still got measurements, but when it warmed to -5, I lost my SSH connection. I'm not sure if that was related to cold.

troylanes
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Re: Enclosure for sub-zero temperature

Sat Aug 13, 2016 2:19 am

This thread is a little old, however, I've currently got a Pi 3 in a thermal chamber at -40C. It'll be doing a soak for about an hour and stepping up through 80C over the next few days along for the ride with some other experiements. Presently, the temp chamber has settled to -40C and the internal temperature sensor [ /opt/vc/bin/vcgencmd measure_temp ] is reading -21C. It's still communicating over ethernet via SSH. I'll update this thread with the final results.

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rpdom
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Re: Enclosure for sub-zero temperature

Sat Aug 13, 2016 3:35 am

troylanes wrote:This thread is a little old
So old that it pre-dates this blog post about Pis being used to monitor penguins in temperatures below -42°C :)

jrperry
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Re: Enclosure for sub-zero temperature

Sat Aug 13, 2016 6:39 am

Thanks for the post I look forward to hearing your results. If you publish them online could I get a link.

Cheers

Jason

troylanes
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Re: Enclosure for sub-zero temperature

Fri Aug 19, 2016 3:36 am

The thermal ramp completed just fine. It started with a long soak at -40C [ approx 8 hours ] with the Pi running the entire time and communicating over ethernet. Over the next several days the temperature was stepped in 5C increments and soaked at each step for multiple hours. The test completed at 80C and the Pi operated nominally the entire time. There'll probably be some thermal shock tests done in the near future [-40C to 80C back and forth as quickly as possible ] and he can ride along as well. I'll post any results to this thread.

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