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Hardware Hacking Power

How to Charge Your Cellphone Using Wasted Heat 214

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."
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How to Charge Your Cellphone Using Wasted Heat

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  • BWM? (Score:2, Informative)

    by brian0918 ( 638904 )
    Bill Winston Ministries?
    • Re:BWM? (Score:5, Interesting)

      by Anonymusing ( 1450747 ) on Monday April 20, 2009 @05:09PM (#27652523)

      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.

  • by Anonymous Coward
    BWM makes awesome cars
  • by thomasdz ( 178114 ) on Monday April 20, 2009 @04:56PM (#27652315)

    I like to work out in my rec. room with various exercise equipment. My favorite? The Carnot cycle (
    I just hop on and convert all the waste heat in the room to useful energy

  • by Finallyjoined!!! ( 1158431 ) on Monday April 20, 2009 @04:57PM (#27652321)
    I could probably power a small village :-)
  • by lobiusmoop ( 305328 ) on Monday April 20, 2009 @05:02PM (#27652403) Homepage

    Given that the average American consumes 13,500KWh per year [], getting a couple of Watt-hours into your phone from wasted heat instead of the grid isn't going to make a damn bit of difference.

    • Re: (Score:2, Insightful)

      Everything starts somewhere.
      • by Toonol ( 1057698 ) on Monday April 20, 2009 @05:18PM (#27652633)
        It's vastly more efficient, and probably less expensive, to redesign the Dryer/Air Conditioner/whatever to waste less heat in the first place. So I'm not really disagreeing with you, but I feel that it's a bit more of a feel good effort than an actual relevant solution.
        • by chromas ( 1085949 ) on Monday April 20, 2009 @05:39PM (#27652965)
          I used to have neighbors who would leave their air conditioners running all day, then, when they came home, they'd let the doors hang open for a while to let some warm in. Less stupid people could help, too.
          • Re: (Score:3, Funny)

            by camperdave ( 969942 )
            Why do air conditioners not come with clocks, so they can be set to be on at specific times?
            • Are you being serious or facetious?

            • by afidel ( 530433 )
              $20 thermostats ARE programmable and pay for themselves in the first month or two, people are just too lazy to use them.
              • by kpainter ( 901021 ) on Monday April 20, 2009 @08:24PM (#27654629)
                I have my thermostat programmed to get me a beer since she is half-way to the kitchen anyways.
              • Those kinds of thermostats hook up to your home HVAC system, not to an air conditioner [].
                • by afidel ( 530433 )
                  What the heck do you think the AC in HVAC stand for? Plus there are programmable wall units, in fact it's even more important with wall units since the lower efficiency means the power savings are greater (less than 10 SEER vs 13+ for whole house units).
            • Because that costs a couple extra cents per unit and causes people to call in because they can not set there clock or return them to stores because they are two complicated. Same logic as to why they still sell microwaves with just a dial. People are generally stupid and making a commercial product requires it to be idiot proof.

            • Re: (Score:3, Interesting)

              by PitaBred ( 632671 )
              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.
          • Fewer [] and less [] mean similar but very distinct things. Precision in language really helps people take you more seriously.
        • by Rich0 ( 548339 ) on Monday April 20, 2009 @06:28PM (#27653603) Homepage

          Additionally, such waste heat might not actually be "free" - depending on some of the implementation details.

          The engine works by generating heat and then converting it to mechanical motion while dissipating that heat to a cold sink. If you don't "waste" that heat by sending it to a cold sink then the engine operates less efficiently.

          Again, it depends on the details - the energy might be "free," or it might just rob the engine of power just as an alternator does. You can't get around the laws of thermodynamics, though...

          • by DirtyUncleRon69 ( 1492865 ) on Monday April 20, 2009 @07:05PM (#27653915)

            I worked at Toyota for a while we have been talking about this for at least a year. The technology has been around for a long time, but we usually call them thermocouples. It's exactly the same concept, except they need to be much larger, and have a much higher temperature differential to be useful. The main problem is the size and weight. The weight is significant when you're looking to reduce mass to improve fuel economy, and obviously it adds cost to the vehicle.

            As for extracted heat reducing the efficiency of the engine, after heat leaves the cylinder head, unless it is used to do work (as in a turbocharger) it is waste.

          • by green1 ( 322787 ) on Monday April 20, 2009 @07:09PM (#27653975)

            Currently automotive engines use a radiator to get rid of excess heat (internal combustion engines generate quite a bit of unwanted heat) usually the combination of a fan, and the movement of the car through the air, serve to cool the radiator so that it can accept more heat from the engine. Without a radiator the car would quickly overheat, which can cause (among other issues) cracked heads and/or engine blocks.

            The alternator currently makes the engine work slightly harder (using more fuel and generating even more heat) to create electricity. By replacing it with a device like this which does not require the work of an alternator, and using the abundant "waste" heat, a vehicle would be more fuel efficient, and as an added bonus, the cooling system would be more efficient.

            The bigger question than whether the engine will be more efficient or not, is whether the extra efficiency gained outweighs the extra costs and complications, and whether the new system can generate enough electricity to power all the accessories and charge the battery, especially on short trips on cold days where it takes longer for the engine to warm up (and therefore start producing electricity) and where the load demanded to start the engine drains the battery further.

          • Again, it depends on the details - the energy might be "free," or it might just rob the engine of power just as an alternator does. You can't get around the laws of thermodynamics, though...

            Thoughtful reply, but it's still likely to be significant. Personally I'd instrument the fool thing to save a few years of controversy, i.e. measure the total effect on an engine with and without this mod. Of course that would be an empirical approach and might offend the theorists (grin).

            I'd also like to think of whether you could get away with a smaller coolant pump if you transferred some of the engine's waste heat through this mechanism rather than simply dumped it through the radiator. I'd also be

        • It's vastly more efficient, and probably less expensive, to redesign the Dryer/Air Conditioner/whatever to waste less heat in the first place.

          If you're living in a cold climate, the exhaust from the dryer ought to go to a heat exchanger to help heat up your house.

          If you're living in a hot climate, it's a waste of energy to use anything other than clotheslines and drying racks.

    • by Hognoxious ( 631665 ) on Monday April 20, 2009 @05:12PM (#27652551) Homepage Journal
      How many cheeseburgers per cubic library of congress is that?
    • Re: (Score:3, Insightful)

      by Anonymous Coward

      Yes, since we can't solve the problem in one step, we should never proceed

      To restate your premise:

      Given that the average American drives 8500 miles per year, spending one day a month bicycling to work isn't going to make a damn bit of difference.

      • by lobiusmoop ( 305328 ) on Monday April 20, 2009 @08:46PM (#27654761) Homepage

        OK fine I will run the numbers for you:
        One day a month is statistically significant at around 3%.

        My cellphone battery is 3.V, 750mAh, or about 3Watt-hours capacity. Emptying/charging it every week of the year gives about 150Wh consumption then, compared to 13,500,000Wh an American uses a year, or about 0.001%. This is statistically insignificant.

        Hopefully that makes things a bit clearer for you.

    • by afidel ( 530433 )
      How about running the AC and all onboard electronics and going to electric power steering, that would probably increase efficiency by ~10%, the equivilant of pulling millions of vehicles off the road if done industry wide (electric power assist is already moving down market due to being an easy fuel efficiency gain).
      • and going to electric power steering

        Why would electric power steering help? If you've got enough torque to run an alternator, you've got enough torque to run a hydraulic pump.

        • by afidel ( 530433 )
          I think it has to do with the fact that you increase friction full time for something that is used some small percentage of the time.
        • The hydraulic pump is running all the time, even if you're not turning. It's much more efficient to have the electric power steering (which is much easier to make variable assistance too) only kick in when you need to turn.
    • One person clapping in an audience of 2,000 doesn't make a damn bit of difference. So why do you bother to clap?

    • Most "eco-friendly" energy sources in fact either cause the same amount of pollution per energy unit or often more, such as biodiesel, ethanol, geothermal, and most wind farms barely break even after huge investment and CO2 emmissions from building them. Solar-thermal is the best renewable source for truly beneficial energy production (except for hydro-turbine of course). All other eco-friendly power projects are just political boondoggles.

      In case you're wondering - boondoogle: a project funded by a gove

    • Maybe not.

      But if we added up all the ideas we are tempted to dismiss due to apparently trivial benefits, we'd probably see a worthwhile dent in overall usage.

  • At last! (Score:5, Funny)

    by goombah99 ( 560566 ) on Monday April 20, 2009 @05:04PM (#27652439)

    finally someone invents a use for the formerly useless lego mindstorms thermal sensor. Use it to let your mindstorms bot find a recharging stations

  • by Joe The Dragon ( 967727 ) on Monday April 20, 2009 @05:06PM (#27652473)

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

  • Thermodynamics (Score:3, Interesting)

    by Hatta ( 162192 ) on Monday April 20, 2009 @05:13PM (#27652567) Journal

    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: (Score:3, Informative)

      by edittard ( 805475 )

      It depends on the temperature difference between the heat source and the heat sink; the higher the difference, the more efficient the conversion.

      P.S. Ever heard of google?

    • by CSMatt ( 1175471 )

      Third law? I thought it was the second law of thermodynamics that says that not all heat can be converted back into energy.

      • by HTH NE1 ( 675604 )

        At least it's easier than constantly muttering block transfer computations into charged vacuum emboitments to hold back the inevitable heat death of the universe.

    • Re: (Score:3, Informative)

      by mmontour ( 2208 )

      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? []

      For each unit of heat energy, the maximum amount of work (useful energy extracted) is (1 - Tc/Th), where Tc and Th are the temperatures of the cold and hot side of the process.

    • by Toonol ( 1057698 )
      For some reason, I vaguely remember that the efficiency of extracting energy from heat is proportional to some power (4th?) of the relative difference in temperature between the object and its surroundings. As a practical matter, I think energy is generally reclaimed by using variations on the mechanical work expansion/contraction performs when temperature changes.

      I'm sure somebody will come by in a few minutes to prove me wrong about everything I said.
    • we obey the laws of Thermodynamics!" -- Homer Simpson

      That would be the second law, that would be broken if you could recover all the heat. The third law is a bit more obscure and basically means that the first two laws apply to everything.

      The amount you can recover varies according to the efficiency of the device you use to recover it, and depends completely on the details of your setup. Obviously no device is 100% efficient (that's the second law again), so you will never be able to recover all of the

    • by AnotherBlackHat ( 265897 ) on Monday April 20, 2009 @05:27PM (#27652787) Homepage

      Obviously you can reclaim some energy from heat, but you can't reclaim it all, as that would break the 3rd law of thermodynamics.

      That's the 2nd law, not 3rd.

      1st law - You can't win.
      2nd law - You can't even tie.
      3rd law - You can't get out of the game.

    • Re:Thermodynamics (Score:4, Interesting)

      by TerranFury ( 726743 ) on Monday April 20, 2009 @05:36PM (#27652919)

      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.

      • by vlm ( 69642 )

        Another point not mentioned is the economics of the situation.
        Inherently the home device is going to raise the temperature of the appliance.
        Higher temp appliance means it wears out faster.
        Wears out faster means lots of energy spent on replacement.
        So, at first glance, what has been designed is a way to save cents of electricity at a cost of dollars of repair work.

        I don't think the car makers will like replacing an alternator with thermoelectrics, because they are immensely big and heavy for the power require

    • by blueg3 ( 192743 )

      It's a constant fraction depending on the temperature difference between the heat source and heat sink. (Plus, many factors that come into play in real system.) This figure comes from thermodynamics.

  • While my own knowledge of thermodynamics is minimal to say the least (never really studied physics at university, got stuck deep in comp sci instead), I seem to remember something about heat tapping generators reducing the thermodynamic efficiency of an internal combustion engine. If an additional load is introduced on an internal combustion engine, whether that be a direct load such as an extra belt on the output shaft to run the alternator or an indirect one such as a "waste" heat conversion alternator, t
    • by eepok ( 545733 )

      It's not "wasted" energy until we refrain from harnessing it. It's not free since we paid for it (by using the product that creates heat as a by-product).

      What this is like, is the "5-second rule". This is scooping up perfectly edible M&Ms off the floor before they rot or the dog gets to it. This heat that is a by-product of reaction is still energy, so it's great that we have a way to pick it up and use it before it dissipates.

      In the end, since we still want to eat M&Ms, we can reduce the overall nu

    • There's no free lunch unless the food was going into the dumpster anyway. Practical engines throw away tons of heat. Heck, that's what your radiator is explicitly for. So since heat is leaking out of your engine at a prodigious rate anyway, you might as well use that flow to power another heat engine (a thermocouple in this case, I guess).

    • If you're taking heat away before said heat moves the piston down, then yes, you're reducing the efficiency, and therefore power output.

      If you're taking heat out of the upper radiator hose, or the exhaust pipe, both of which are just dumped out to the atmosphere, anyway, then it really is waste heat, and you're not reducing the efficiency of anything.
      Recover enough heat, and you might be able to do with a smaller radiator and cooling fan, though, which, while it wouldn't increase the efficiency of the engin

    • Yes.
      There's a post above about the carnot cycle which is theoretically the most efficient engine for turning heat into useful energy. The carnot cycle efficiency is equal to 1-Tc/Th

      Basically, the hotter your furnace and the colder your exhaust, the more efficient your system is. So if you have some powerplant's waste heat, it's not useful to you unless you have some reservoir of cold to dump that heat into while running your cycle. Obviously, it is more efficient to apply that cold reservoir to the original

  • by mc1138 ( 718275 )
    I totally made a joke about this a few days ago... []
  • How much energy is produced? I'd imagine not a lot. How much does it weigh? Does it cost more in fuel to lug these around than they can produce? You'd need one at the exhaust, one at the engine, one at the brakes..

    Is this another deal where I spend $1000 and get 5w/hour?

    • More importantly, how does it compare to a $50 dash-mounted solar cel?
    • Devices like these are usually silicon wafers.
      They will weigh less than your alternator.

      And you'll only need one. Probably connected to your coolant line before the radiator to get it good and hot.

    • by blueg3 ( 192743 )

      I'm not familiar with the specific technology here, but most of these heat-recapture systems are Peltier systems. Compared to their power output, for something the size of a car, they're fairly light. Some of them are cheap enough to make -- they're what runs solid-state cooler chests -- but I'm only really familiar with research models (which are hard to price).

  • JTEC []. Use this, drop the alternator as well as the serpentine belt and move towards an all electric system. This would allow them to move a GAS car to an electric powered steering (or perhaps a motor driving hydraulic pump), a heatpump that would also go into an electric car. This would allow a car company to more easily move towards electric cars.
  • "It was the G1-1.4-219-1.14 $75 from tellurex."
    Using "waste" sure is expensive...
  • 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 sa

  • Cooking [] on your car's engine.

  • by macraig ( 621737 ) <> on Monday April 20, 2009 @07:01PM (#27653883)

    I wanna use my huge bank of toasty little wall warts to charge my cell phone. If I can do that the lazy little power-sucking tribbles might finally justify their existence.

  • by kheldan ( 1460303 ) on Monday April 20, 2009 @07:06PM (#27653925) Journal
    Peltier Junctions are really old news, they're not very efficient at all, they don't last forever, and they're not particularly cheap. TFA doesn't have anything new to say or any links that have anything new to say. Mod the entire post down to -1, Useless post and move on.
    • by blueg3 ( 192743 )

      they're not very efficient at all, they don't last forever, and they're not particularly cheap

      So... like an internal combustion engine, then?

  • How %efficient are these thermoelectric devices in outputting electric power W from the power W extracted by cooling the wastefully hot devices? And how much power does it take to manufacture one of these thermoelectric devices?

  • by anwyn ( 266338 ) on Monday April 20, 2009 @09:42PM (#27655193)
    I have a secret plan to run ipods off of the Cosmic microwave background radiation.

To avoid criticism, do nothing, say nothing, be nothing. -- Elbert Hubbard