How to Charge Your Cellphone Using Wasted Heat

Ilya writes "Companies such as BMW are investing in Thermoelectric Generators to make their cars more efficient by replacing the alternator. Thermoelectric Generators convert wasted heat from the engine into electrical power. This green instructable shows how you can use the same technology right now at home to harvest expelled heat from home appliances to charge your cellphone and other gadgets. Also features a lego racer powered by the roaring flames of a tea candle."

Comments

Re:BWM?

[Anonymusing]

Seriously: major typo in the summary, folks.

Many years ago, I worked with an ad exec who had (much previously) pitched a campaign to BMW. His agency lost the bid to another agency, even though they thought they had an innovative ad concept. Some months later, he was reviewing the posters and realized they had printed "BWM" in multiple places, in very large type, and nobody at the agency had noticed prior to the presentation. Ooops.

Thermodynamics

[Hatta]

This is something I never quite grasped from physical chemistry class. Obviously you can reclaim some energy from heat, but you can't reclaim it all, as that would break the 3rd law of thermodynamics. How much energy can you actually reclaim from a given amount of heat? Is it a constant fraction, if so where does that number come from? Is it variable? If so, what does that number depend on?

Re:Thermodynamics

[TerranFury]

As other posters have mentioned the physical limit you're concerned with is the Carnot efficiency.

One view of things not yet mentioned by posters is that energy is not what matters but exergy -- the capacity to do work. A bathtub full of lukewarm water contains a great deal of energy, but little exergy. In general, electrical and mechanical energy has a lot of exergy; thermal energy is as low-exergy as you can get, especially at low temperatures.

Note that the above is really just a rephrasing of the idea of entropy.

Re:laptop heat? can that be used to charge it self

[Joe The Dragon]

but you will get longer life out of it then?

Re:laptop heat? can that be used to charge it self

[Anonymous Coward]

Yes, you will get longer battery life if you turn some of the "heat" into electricity. There are some problems to look out for, though. The thermocouples don't really convert heat into electricity. It's the temperature difference between the hot and the cold side which creates the electricity, so you have to have a heat source and a heat-sink capable of sinking the heat without warming up too much. Since the cool side has to stay cool, the temperature difference between the air and the heat-sink is low, which means you need a much bigger heat-sink than normally. (The instructable shows a thermocouple with heat sink mounted on the side of a bike exhaust: the additional drag probably costs more energy than the device can extract from the heat difference...)

Re:BWM?

[DNS-and-BIND]

Haha, good one. How about this? Leftist terrorists were discovered - their plot was to dress as police and then open fire, but they spelled police wrong on their motorbikes, and were arrested when real cops spotted the mistake.

Saw research into much larger scale uses of this

[Jared555]

I was visiting Illinois State University's physics department because I am planning on attending this fall. They were working on a material along these lines with a fairly high efficiency rate but they were just starting actually trying to make small amounts of the material.

Their intended use of the material would be in steel foundries, etc. where millions of dollars are spent on power and even something not very efficient could save a ton of money.

From what I gathered talking to the professor there the same efficiency increasing techniques could be used even with smaller temperature differentials as long as you had different materials used.

Sorry but they don't have too much information on their website. They had a few posters with information in the building but not much online.

http://www.phy.ilstu.edu/programs/research.html

A link to the professors bio:
http://www.phy.ilstu.edu/facandstaff/marx.html

Re:Sipping From a Firehose

[PitaBred]

Some do. Actually, some of them even come with these nifty "thermostats" where you can have them come on only when it gets too hot. And if you look even more, you can find a thermostat coupled with a clock so you can set it to different temperatures at different times! Technology really is amazing.