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Caframo ecofan thermoelectric device

  1. Jan 30, 2009 #1
    I have an ecofan that sits on top of my woodstove. It is powered by the thermo reaction between 2 metals, thus exciting electrons which then power the fan. Great device for moving air around the cabin. Living off the grid in rural Alaska, I'm in search of a larger device that could produce 12 volts to charge the battery bank. The woodstove is in near constant operation for the winter months. Wondering if anyone has ideas how this could work, or seen a product out there?
  2. jcsd
  3. Jan 31, 2009 #2


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    Staff: Mentor

    A steam engine would be much more efficient. Thermoelectric converters have a very low efficiency. You can search at wikipedia.org for more info on the efficiency of different kinds of engines and converters.

    Welcome to the PF!
  4. Feb 1, 2009 #3
    Hi Berkeman. Efficiency may not be the issue here, because any waste heat ends up heating the room, as was the original intent anyway. The issues might be cost, practicality, if the OP can implement it, and if enough energy can be stored to make it worth while.

    Come to think of it, could it be located in the flue?
  5. Feb 1, 2009 #4


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    Thermoelectric devices work from there being a difference in temperature between two different metals or semiconductors. If you could have one side outside in the cold and the other side on the stove, you might be able to get enough current for battery charging. For example, you could get 3.5 amps at 4.2 volts but you would need a 200 °C temperature difference. http://www.customthermoelectric.com/powergen.html?gclid=CPm8gPnVu5gCFR0SagodRT-0bA
  6. Feb 1, 2009 #5


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    Excellent! The last time I was to their site, they didn't list a price for their power generating modules.

    mikealaska, I don't know your background so I'll just do a little stream of consciousness post, so please ignore anything you already know:

    12 volt batteries are fully charged at around 12.7 volts. So you will need at least 4 of the devices listed(@$108.50 each) for a charging system. My solar panels run at a no-load voltage of between 16 and 18 volts DC. This seemingly high difference in voltage(18VDC source vs 12.7VDC battery) is required because of internal resistance of both the battery and power supply.
    The the voltage generated by the peltier stack is linearly proportional to the temperature difference so you will have to maintain the 200 °C delta T, otherwise the voltage will drop and you won't have a charger. I'm starting to think that you may want an intelligent DC to DC converter. This would actually require you to only purchase one of the peltier stacks.
    But given that deep cycle batteries have a capacity of ~1kwh, a single generator would take over 60 hours to charge one fully.
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