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Author Topic: minimum temperature for electronics/mini-heater  (Read 1109 times)
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Hi!

I need a device which works under 0 degrees Fahrenheit. I suspect for all the parts I intend to use (Arduino, touch-LCD-display, battery (Li-Po?)) this is a bit too cold. On the other hand, I know there are things which do work in these conditions.

I know, there are datasheets which say in which temperature ranges these devices work, but if I order such a LCD, there are so many components on it which I dont know and can't see, I won't know what their temperature range is. So probably a mini-heater or something in the case would be the good solution. So what do I have to look for? Does something like this exist?
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Most electronics will work fine around 0 degrees F.  The ATmega chip is rated to -40 degrees C*.   But, I wouldn't trust the "average" LCD, and batteries don't usually work "perfectly" when cold either.

A Mini-heater should be easy to build.   You can just use resistors (probably 2W resistors or bigger... 10W (or more) resistors are common too, so it wouldn't be hard to make a 100W heater..    All of the power dissipated in a resistor is converted to heat. 

The hard part is calculating how much power you need.   If you have a small insulated box, less than 10W will probably be enough...   You'll probably just have to experiment to see what kind of heat-rise you can get.   In case you don't know, you can calculate power (Watts) as Voltage squared divided by resistance.   (And, the power dissipated in parallel resistors simply sums-up.)  As a rule-of-thumb, you should use a resistor rated at twice the actual continuous-power.   

Since this thing is apparently battery powered, all of the power is going to come from your battery!   The heater is most-likely going to take more power than the circuit.   

Are you going to run the heater full-time, or will you have a temperaure sensor and turn it on only when needed? 


* WOW!  I just realized that -40 is an "interesting" number when converting between Fahrenheit and Centegrade!  smiley-grin
« Last Edit: October 10, 2012, 05:58:21 pm by DVDdoug » Logged

Ayer, Massachusetts, USA
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Also note that batteries tend to have discharge faster at colder tempertures (http://chemistry.about.com/od/howthingsworkfaqs/f/coldbattery.htm)
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Quote
* WOW!  I just realized that -40 is an "interesting" number when converting between Fahrenheit and Centegrade! 

It's the only one Fahrenheit got right. I only know this because I live in a place that gets -40 temperatures on occasion.

People used to Centigrade often don't realize how cold 0 Fahrenheit is. (-18C - a chilly day, better wear a touque)
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I think that for low temperature performance, nickle-cadmium is the best rechargeable chemistry that is readily available to a consumer.
For primary cell chemistry, 1.5V lithium cells have a great reputation for performance in the cold.

My personal experience is that lithium rechargeables are a waste of time below about 5C.
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As a liquid crystal physicist, I can tell you that LCDs don't work at that low temperature. You may consider LED display on the other hand.
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Thanks for your replies. Yes, I will have to use NiMh batteries, no problem. For the temperature, i would probably use a PID and a temperature sensor.

But I think it wont work to heat an LCD from behind. The heat wont arrive on the front side without heating extremely. To make it a bit clearer, I am a Hot Air Balloon pilot, and we do have instruments with huge LCDs (although black and white and without touchscreen, but they are 15x8cm) which work under these conditions. Since it is an device for flight safety I wont open it to look how they're doing it.

Do there exist like LCDs that are made for these conditions? Any other solutions?
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Just for the record, I know from experience that you can get some electronics to work at a few milliKelvin.

Not LCD's, though!
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As a liquid crystal physicist, I can tell you that LCDs don't work at that low temperature. You may consider LED display on the other hand.

There were a few days last winter were the liquid crystal display in my truck turned into a solid-crystal display. Seemed to work fine after it thawed though.
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As a liquid crystal physicist, I can tell you that LCDs don't work at that low temperature. You may consider LED display on the other hand.

There were a few days last winter were the liquid crystal display in my truck turned into a solid-crystal display. Seemed to work fine after it thawed though.

Yes, exactly what I was talking about. Liquids solidify. You are lucky the process didn't damage liquid crystal alignment too much. It will damage alignment in general. Then the display will be more white washed than before until the thing just can't be read anymore.
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To make it a bit clearer, I am a Hot Air Balloon pilot, and we do have instruments with huge LCDs (although black and white and without touchscreen, but they are 15x8cm) which work under these conditions. Since it is an device for flight safety I wont open it to look how they're doing it.

I bet they do have heaters. Have you looked into Kapton flexible heaters? Very nice to have around electronics. Some batteries even have heaters to maintain operating temperature.
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A Vacuum Fluorescent Display will work down to -40.

Finding small VFD displays won't be hard but finding one with a touchscreen probably will be.
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