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Power for an outdoors project
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

Power for an outdoors project

by stephanie on Wed Jan 19, 2011 9:27 am

I'm putting together a few sensors and a stripped-down Arduino and an XBee that I want to set up outside. It'll be periodically transmitting the sensor signals to another Arduino & XBee indoors. The 'stripped-down Arduino' is basically just an Atmega168 with the Lillypad 168 bootloader on it, so it's running at 8MHz with internal oscillator. This is to keep the parts count down, and also because I happened to have a spare 168 laying around. :)

The conditions outside, over the course of a year, can range from -40 celcius (rare but it happens) to +40 celcius (also rare, but it happens). From what I've been able to find, the components are ok with this temperature range (though it might get iffy at the worst of the cold weather). I was thinking to run the whole thing at 3.3v so that I don't need to worry about multiple voltages and level shifting etc.

There is a power outlet that I could use, if I can find a weather-proof power adaptor. I don't know if adaptors are suitable though, for that wide of a temperature swing? The other option is batteries. I could wire 2 or 3 "D" cells in series and run that through a regulator.

My concern is to maintain the 3.3v consistantly - some of the sensors rely on the ADC and if the supply voltage varies then the readings will be inconsistant.

Any thoughts, suggestions, comments, would be most-welcome.

Thanks!
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Re: Power for an outdoors project

by adafruit_support_bill on Wed Jan 19, 2011 9:48 am

Batteries are not going to do well at those extremes, but if you have a power outlet there I'd use it. For industrial and transportation applications, it is not unusual to put heaters and/or coolers in the enclosures to keep the instrumentation within operating limits. Heating can be cheap and compact. Cooling options are more expensive.

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Re: Power for an outdoors project

by stephanie on Wed Jan 19, 2011 12:22 pm

Thanks for the info!

Actually one of the sensors is temperature, so I wouldn't want to have heating or cooling in there...

The reason I had considered batteries is that I have one of those clocks that reads the outside temp and it does so with a little transmitter that runs on 3 AA batteries. It tends to run about 12 to 18 months on a set and it seems to survive. It sometimes stops working, eg. at the extreme cold, but it starts up again when it gets warmer.
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Re: Power for an outdoors project

by zener on Wed Jan 19, 2011 1:14 pm

As I recall the best low temp rechargeable battery chemistry is NiCd which is -25C (from my menory...) I don't think I ever researched primary batteries (non-rechargeable). However, it doesn't mean it dies at that temperature, just loses capacity. So if your draw is minute then probably OK. You can find a lot of info around on this subject.

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Re: Power for an outdoors project

by franklin97355 on Wed Jan 19, 2011 1:17 pm

Actually one of the sensors is temperature, so I wouldn't want to have heating or cooling in there...
Actually you would not want your sensor in there. It should be outside the enclosure to get a valid reading.

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Re: Power for an outdoors project

by stephanie on Wed Jan 19, 2011 1:29 pm

franklin97355 wrote:Actually you would not want your sensor in there. It should be outside the enclosure to get a valid reading.


Hmm good point. I had been thinking of making the enclosure slotted or not putting a bottom on it, to allow air flow in and out, but that might not be good enough. I'll have to think about how to weather proof the temperature sensor on its own. Maybe just coat it in epoxy or something like that.

Actually - I wonder how long the leads could be on the sensor... it'd solve the whole outdoor power supply problem if I could leave the arduino indoors and just run a length of cable outside. Hmmm...
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Re: Power for an outdoors project

by adafruit_support_bill on Wed Jan 19, 2011 1:59 pm

For an outdoor installation, you will want the enclosure to be sealed up good. Weather is only one concern. Nesting insects and possibly other critters would be another. You will want the temp sensor outside the enclosure so that it won't be influenced by the waste heat of the batteries and circuitry. You can dip your sensor in epoxy or seal it in a tube.

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Re: Power for an outdoors project

by uoip on Wed Jan 19, 2011 3:02 pm

Some random thoughts of various alternatives:

Lithium AA cells have very good cold weather performance. And long life.

Hardware stores sell weather-resistant outdoor outlet covers. They may be big enough to protect a small wall-wart style plug adapter from moderate rain. Here's the first picture of one I found on google (this is not an endorsement of the supplier)

http://www.smarthome.com/25501/1-Gang-I ... HMC/p.aspx

You could put an adapter indoors, and run some low-voltage lighting cable out to your project. There may be some voltage drop in the cable if you have a long run, but if you have a linear voltage regulator out at the site where the arduino is, you don't care much about voltage drop in the wiring. For the types of low current requirements I'd expect from an Arduino, xbee and a few sensors, I'd just use a 12VDC adapter and put a 3.3v linear regulator at the other end. The cable sold at hardware stores for 12V landscape lighting is suitable for above ground use outdoors in the sunlight, or suitable for burial under a few inches of dirt.
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Re: Power for an outdoors project

by Entropy on Wed Jan 19, 2011 4:45 pm

Stephanie wrote:
franklin97355 wrote:Actually you would not want your sensor in there. It should be outside the enclosure to get a valid reading.


Hmm good point. I had been thinking of making the enclosure slotted or not putting a bottom on it, to allow air flow in and out, but that might not be good enough. I'll have to think about how to weather proof the temperature sensor on its own. Maybe just coat it in epoxy or something like that.

Actually - I wonder how long the leads could be on the sensor... it'd solve the whole outdoor power supply problem if I could leave the arduino indoors and just run a length of cable outside. Hmmm...

What you might be able to do is run power/ground on some of the pairs of a Cat5 cable, and then use a differential driver chip (such as a SN75176) to send serial data over another pair using RS485 differential signaling.

Wireless is nice, but when you start having to worry about power like this, it may be easier to just run some Cat5.
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Re: Power for an outdoors project

by franklin97355 on Wed Jan 19, 2011 10:25 pm


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Re: Power for an outdoors project

by mike31416 on Thu Jan 20, 2011 7:59 am

Hey,

Actually - I wonder how long the leads could be on the sensor... it'd solve the whole outdoor power supply problem if I could leave the arduino indoors and just run a length of cable outside. Hmmm...


I put a TMP36 Temperature sensor (-40�C to +150�C) in a 2 foot piece of copper tubing (leftover from a line run to my refrigerator ice maker). I crimped and sealed one end and slid the sensor and wire to the bottom of the tube and then sealed the top around the wire with silicon sealant. The sensor just fits in the tube's diameter. I have about 8 feet of wire connecting that to the controller's analog input. I had to add a capacitor at the input because I was seeing noise when the usb or wall wart was connected to the controller.

Don't know what the maximum length could be, but you could try the length you need in a test setup before you commit to making the end product.

I use this for a beer homebrew time and temperature monitor program.

Mike

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Re: Power for an outdoors project

by stephanie on Thu Jan 20, 2011 8:56 am

Thanks for all the suggestions! I've got lots to think about now.
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Re: Power for an outdoors project

by Ramjet1 on Wed Jan 26, 2011 11:04 am

You could put all the goodies in a NEMA weatherproof box and epoxy or silicone any through holes for wires, sensors, etc. A small solar cell pushing an internal nicad charger might do the trick.
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Re: Power for an outdoors project

by Ramjet1 on Wed Jan 26, 2011 11:07 am

Look into a peltier device to deal with heating/cooling inside the box. An internal temp sensor and a couple components could reverse the opacity based on internal temp.
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Re: Power for an outdoors project

by Ramjet1 on Wed Jan 26, 2011 12:21 pm

Should have sai ' reverse the polarity'
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Please be positive and constructive with your questions and comments.