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Cold box power problem

  1. Mar 14, 2008 #1
    Hello all,

    I'm having a bit of a problem on a class design project. We have to design a mini-fridge for developing coutries that runs on its own power and must cost under $100 ideally (it can go over if necessary). My group decided to use a hand-crank powered thermoelectric module and fan assembly to cool down a 5ml vial inside a foam-filled food jar smaller than a lunchbox. We're having problems running it though, because our cranks produce barely enough current to run only the TE module, and there is only a slightest cooling effect.

    My idea is to use solar panels to operate an op-amp that can amplify the power from the hand crank to run both devices. It's been a few years since I took circuits so I don't even know if this makes physical sense. I'm just wondering whether it can be done within or without the monetary constraints.

    I'm also open to any other ideas for powering this thing. Other constraints include portability and a cooling capability down to below 10 celcius. It should ideally stay that way for up to 12 hours, but again, these are bendable constraints.

    I'd really appreciate the help. Thanks in advance.
  2. jcsd
  3. Mar 14, 2008 #2


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    Geez, and I thought that I had a weird avatar... :rolleyes:
    My only suggestion, since I don't know anything about refrigeration, is to build in a very flexible power system. Ideally, given the purpose, it should be able to use a water wheel, a mule on a tether, maybe solar and wind power, fire...
    The more adaptable it is (without incurring horrendous construction costs), the more useful it will be on a large scale.
  4. Mar 14, 2008 #3
    The op-amp idea doesn't make physical sense to me. Op amps are amplifiers, but they amplify or isolate signals, not power. If you're using solar panels, you might as well use the power generated by the solar panels to run the equipment, and supplement the power with the hand crank. I know absolutely nothing about thermoelectric modules, but I know enough to ask the question: How sensitive is it to input current/voltage? If the thermoelectric module is sensitive to inputs, then there is a chance you will need some kind of voltage regulator to ensure that someone cranking away doesn't overpower a circuit.

    Danger's idea is a good one, and from my limited knowledge of refrigeration and circuits, you'll probably just need a regulated power supply to ensure you get usable power. The bugs or microcircuits that you need can be had for cheap, especially for something that size.


    Also, some power storage mechanism would also be very useful (this doesn't need to be a chemical battery necessarily). In fact, I remember seeing an ad for a lamp that was powered by weights that the user lifted. As the weights gradually fell afterward, they powered the lamp. Recharging just required lifting the weights.
    Last edited: Mar 14, 2008
  5. Mar 22, 2008 #4
    Well...I'm actually doing the exact same project as ye for my final year project! Did ye get the project specification from the engineering world health organisation?? I was wondering if ye got anywhere with the power source for the T.E. module?? I think i will be using photovoltaic/battery system in my design because cranking or shaking d'ont seem to provide enough power as you mentioned.

    I d'ont think i will be using a fan in my design as i came across a study that found that using a natural chimney to reject the heat could improve the performance of the refrigerator and the fan current could then be used for cooling. The name of the journal is "Heat rejection alternatives for thermoelectric refrigerators" by H.Sofrata.

    I can't seem to find good information on cranking or shaking applications..would ye mind telling me how much power it takes to run your refrigerator, is it around 4 watts?? and how much power ye generated from the cranking system..and would ye have to crank it constantly to power the T.E. module?

    Anyways...might as well keep in touch...could help eachother out with this project!!
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