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Hibernating device

First draft of a hibernating device

For the past few days, I've been thinking over and over about an electronic device that could hibernate. One thing that strikes me here is the very fast pace at which weather and illumination change throughout the year. At this time of the year, daylength is about 14 hours. It will drop by 5 minutes every day until it reaches about only 5 hours by mid-december...

At that time, temperature will go down to -30 °C and even lower, according to locals. The lowest recorded temperature was -55.8 (February 11, 1979). Given these conditions, combined with the inhabitants' reputation as being heavy drinkers, it is not a big surprise to learn that people often lose toes due to frostbites around here. It has even given to a local, absolutely disgusting attraction, involving "drinking" a real human toe.

Anyway, coming back to the subject at scope, I thought it could be interesting to think about how an electronic device could survive through winter. I started with the idea of using a "pole" (like, a PVC tube would be perfect) part of which would be under the ground, to help for insulation against the cold. I thought about several ideas, I'm still hesitating between using sound, light, or both. Soundwise, I'd like to have the device emit a "whistling" sound from under the earth, there's kind of a creepy feeling to that, I like that. I also like the idea of using LEDs, maybe somehow mimicking the Northern lights. I like this mood lamp among other things.

After a lot of thinking and a long chat exchange on the AVR Freaks IRC channel, I came up with a few notes and strategies.

  • There should not be much thermal problems if I burrow the device 36'' (90 cm) under the ground.
  • Use a lot of insulations.
  • Don't use electrolytic capacitors (use ceramic, plastic, etc).
  • Batteries lose efficiency in cold, preferably use NiCd instead of NiMH or use ultracaps.
  • LEDs work fine in cold conditions.
  • Speakers should work, preferably use a plastic one. It might be a bit tricky though, the cold can kill it even if it's not being used during winter.
  • Making a heater circuit can be tricky, should try to avoid it. Peltier device or element could work, but the main problem is that all of these require a lot of power.

Statistics about daylength and illumination in Whitehorse (in French)

For the past few days, I've been thinking over and over about an electronic device that could hibernate. One thing that strikes me here is the very fast pace at which weather and illumination change throughout the year. At this time of the year, daylength is about 14 hours. It will drop by 5 minutes every day until it reaches about only 5 hours by mid-december...

NiMH datasheet

Duracell' NiMH datasheet explains in details the consequences of temperature on NiMH batteries.

Another graph I found elsewhere on the web that seems to confirm my experiments:

That sounds like it could be

That sounds like it could be actually helpful in a way. During winter, the solar panels are expected to generate a lower voltage, which means that they couldn't help in recharging full batteries for instance. But since the temperature drops, so does the apparent voltage from the batteries, allowing the electricity from the solar panels to flow even if they generate a lower voltage. I believe the batteries' charging efficiency also decreases, though, but at least it could allow them to "stay put" through the harsh winter.

Li-on

Li-on batteries are supposed to withstand cold weather without any problem. I think they require a much more complex charging circuit though. Still, it's something to investigate.

NiMH in cold weather

I ran some tests with NiMH in the freezer and fridge today. NiCad would be better I guess but they're pretty nasty environment-wise.

I found a few discussions about NiMH from different sources.

Cold Weather Battery Performance: NIMH vs. Lithium from a photographers' forum.

Some interesting replies:
"I use 1300 mAH NiMH batteries in my EOS 3 power booster. In December at Bosque I shot 15-20 rolls per day, with battery-sucking 500/4.5 and 300/4 IS lenses at 6 FPS and AI Servo AF mode. Typically it would go above freezing as the day progressed, but it started out very cold, probably below 20 F.

I wouldn't hesitate to use NiMH batteries in the cold, so long as you can recharge them each day."

"At -4 degrees F both NIMH AA and Lithium CR5 batteries are down to 1/2 normal capacities. At 32 degrees F both are down to between 90% - 95% of capacity. Alkaline AA cells are down to 65% at 32 degrees F and useless at -4 F. "

"I am in North Dakota and shot the lunar eclipse last month in -12F temperatures using a 2CR5 battery in my ElanIIe. It was subjected to these temperatures for over 3 hours and I still had power to shoot to the end."

NiMH reduced performance in cold weather from an EV forum

Replies:
"It´s because of the chemistriy of NiMh-Batteries. The internal resistance of the batteries becomes higher at temperatures below 0°C so they "seem" to be empty earlier. Onother problem is that the batteries which are "hit" by very cold cooling-air "seem" to be empty earlier than the other warmer ones."

"I've red on a RC forum here in Holland that NiMH behave like this:

15-30 degrees Celsius (100% SoC)
10 degrees Celsius it is 80%
0 degrees Celsius it is only 60%
-10 degrees Celsius it is only 15%!!"

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