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Air conditioning on a budget

Discussion in 'General Electronics Discussion' started by Harald Kapp, Mar 31, 2014.

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  1. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Normally noise is an annoying feature of electronic circuits. As designers strive to minimize power consumption, voltages and currents decrease while resistances within the circuits increase. At the same time, operating frequencies and with them bandwidth increase.

    As we know, the thermal noise voltage of a resistor is given by this simple relationship:

    Vnoise= √(k*T*B*R)

    k= 1.38*10^-23 J/K = Boltzman constant
    T = absolute temperature in degrees Kelvin
    B = bandwidth in Hertz
    R = resistance in Ohm.

    Example: at room temperature (~300 °K), a bandwidth of 1 GHz (not uncommon for modern processors) a resistor of 1 MOhm will develop an RMS noise voltage of ~4mV (RMS).
    Let’s turn this unwanted noise to our advantage with this little circuit:


    An RMS voltage of 4mV is not enough to get the diode conducting (although some peaks of the noise will be well above 4mV due to the statistical distribution of the noise voltage. But we can easily use a 10GOhm resistor creating ~400mV (RMS) noise voltage, just enough to open a Schottky diode. If we put a few of these resistors in series, e.g. 10 resistors, we create a 100GOhm resistor which will supply ~1.3V (RMS) of noise voltage. Subtracting 0.3V for the Schottky diode, the capacitor will be charged to ~1V, enough to drive some low energy circuit.

    Alternatively, a high Ohm resistor can easily be constructed from two parallel wires laid out in a few centimeters distance in air without actually touching each other. Resistance and therefore output voltage can easily be adjusted trimming the distance between the wires. Take care not to overload the diode and capacitor!

    The resistor will be cooled since the energy drawn from it in form of electrical charge is taken from the input of thermal energy to the resistor.

    Now for the fun part: Build a few of these generators, e.g. 12, and power a fan, e.g. a 12V PC fan, from them. Use the fan to blow warm air to the resistors to compensate the loss from the conversion of thermal to electrical energy. The air will be cooled (because thermal energy is transferred to the resistors) and you have free air conditioning. The hotter it gets, the more electrical energy is created by the resistors, the better the air conditioning will work.

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  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    For those in colder climates, using a very high resistance (say the 100Gohm mentioned above) and then force this voltage through a 1 ohm resistor. You can use the resulting heat to warm the resistor, further heating it.

    The end result is that both resistors get very hot and the surplus heat can be used to warm your house or even to boil water and run a stem turbine to generate electricity.

    Incidentally this is a reason why you should never place a low resistance in parallel with a high resistance. People doing this have started fires and runaway thermal processes.

  3. BobK


    Jan 5, 2010
    Isn't April 1 tomorrow?

  4. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    What has the date to do with that clever invention?
  5. flippineck


    Sep 8, 2013

    You just rig up an antenna, any old antenna will do, it's going to resonate at some frequency or other right?

    Then just stick a diode in the transmission line. Rig up say a few hundred, and feed the resultant pulses into a battery. end up with a battery full of electrons in no time yea?
  6. davenn

    davenn Moderator

    Sep 5, 2009
    hahaha :)

    that brings up the other issue of misunderstanding

    Its amazing how many people out there believe that a full battery is full of electrons and that the reason the battery goes flat is because all the electrons are used up !

  7. flippineck


    Sep 8, 2013
    well you're half right (as Morrissey said)
  8. shumifan50


    Jan 16, 2014
    A bit like spaghetti trees on BBC then.
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Except the spaghetti trees are real (I saw them on you-tube)
  10. shumifan50


    Jan 16, 2014
    I saw then on the BBC news channel LOL. They even explained how long it took to cultivate the trees to produce the exact lengths to fit the boxes.

    But this aircon is also true. It is on
  11. jpanhalt


    Nov 12, 2013
    1957 -- I had just started high school. The Los Angeles Times ran a picture of the Queen Mary in the LA River. We heard nothing about the spaghetti tree.

    The Brits did a much better job:

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