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Q & A: Powering a clock with the weather

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Most recent answer: 10/22/2007
Q:
About clock mechanisms. Is there a system by which the constant change in atmosphere pressure will power a clock? How is this accomplished?
- Rich Gerhard
CoeurdíAlene, Idaho USA
A:

  Hi Rich,

  Well, I guess you could do it.  The atmosphereís pressure changes due to varying weather patterns as you say.  Since the weather is variable, sometimes it may even stubbornly refuse to vary for a while, but usually, in most places, you can anticipate small changes in atmospheric pressure.  You could get a large can with a piston in it, and seal it up so that the contents of the can never change.  Then the piston should go up and down as the ambient pressure changes, and you might be able to extract some work from that (Iím not sure how to to it the best, since the displacements are likely to be small for reasonably-sized cans, and electrical generators like circular motion). You might be able to put some kind of ratchet system for winding a spring up using this arrangement, too, but your clock has to use very little energy.  A mechanical barometer uses this kind of approach for moving a dial around -- there isnít much energy available this way, though.

Perhaps the most practical system I can think of is in a noisy environment, you might be able to extract enough energy from the acoustical waves impinging on a microphone (or even just use an ordinary speaker).  Use a rectifier and charge up a capacitor or battery.  Find one of those little LCD watches which lasts five or more years on a tiny battery, and you probably have enough energy from that to power it.  You might have to take care to make sure that the voltage is regulated so as not to fry the electronics, so the battery approach might be better.

You can get more energy out of air motion with a windmill, of course, but perhaps thatís not what you were asking.

  Tom

(published on 10/22/2007)

Follow-Up #1: Atmos Clocks

Q:
I believe that the question of powering a clock with changes in atmospheric pressure can and has been best answered with the "Atmos Clock" fully functional clocks that are powered by changes in atmospheric pressure. Examples of this clock, and more information about how it works can be found at:

http://www.compadapt.com/atmos.html
http://www.compadapt.com/howitworks.html

Arthur Beverly also designed a clock that has been running (except for cleaning, moving, etc.) without winding since 1864.

Hope this helps.
- Arthur Spafford
Hidden Hills, CA, USA
A:

  Hi Arthur,

  Thanks for the follow-up!  The clocks depicted on that website are truly amazing, and lots of fun -- interested people should definitely take a look at them.

  The explanation and the advertising seem to point rather to temperature variations as the source of energy needed to run the clocks.  I neglected these in my previous answer -- sorry -- they are probably more important than external pressure variations.  As temperature increases, gas pressure goes up, or expands if it can, or does a little of both, according to PV=nRT, the ideal gas law, where P=pressure, V=volume, n=number of moles of gas, R=gas constant, and T is the absolute temperature (in degrees Kelvin).  A change in the ambient temperature will make the gas inside the can and outside expand, but the gas outside has someplace to go (external winds equalize pressure over large areas), while the pressure in the can changes a lot.  Itís the change in the pressure in the can relative to its surroundings which allows work to be done (however tiny an amount).  Quite clever!

  You could experiment with one to see if pressure variations alone are sufficient to power it.  Put an Atmos clock in a temperature-controlled room and see if it runs out of energy.  Of course they donít need much of a temperature change -- one advertisement says a 2-degree change in temperature is enough to power it for 48 hours.  There might be enough energy in the pressure changes alone to do it.

  Iíve seen advertisements of watches that wind themselves up with everyday wrist movements.  Typing answers to Physics Van questions would be more than enough for one of these.

  Clocks and calculators take very little power to run, and so they are great playgrounds for engineers to come up with all sorts of clever energy sources.  The advertising line that they are "more ecological" than other clocks is not right, however.  All the clocks on the page are bulky, have big pieces of metal and glass, and are very costly.  Just transporting one from the factory to your house takes lots of fuel, not to mention whatís needed to smelt the metal ores.  If you want to be ecological, get a wind-up clock or a cheap, tiny LCD battery-powered clock.

Tom

(published on 10/22/2007)

Follow-up on this answer.