Peltier campfire generator put out 14W (kind of)

peltier-campfire-generator

This is the control and monitoring hardware which [Jack] built for his campfire electricity generator. He’s done an amazing job to get this far. You can see he’s pulling 1 Amp at 14.2 Volts off of the system. But there one gotcha that’s still plaguing him.

The rig uses a big metal plate as a heat sink over the campfire (which is simulated by a cooking stove for testing). On the back of that plate is an array of Peltier coolers which generate electricity based on the temperature difference from one side to the other — it’s the same theory behind candle generators. The cold side has a heat sink with water running through it. What you see above are three relays which switch between using the Peltiers in series or in parallel based on their voltage output. You can’t really make it out there but there’s a radiator and recirculating pump to the right which are used to cool the water. The gotcha we mentioned is that the radiator can’t quite keep up with the heat of the fire. To get the results seen above [Jack] is running cold water from the tap through the radiator. But maybe if this were used in the winter the water could be circulated through a big box full of snow. Just keep shoveling it in to keep up the electrical potential!

After the break we’ve embedded part four of the project video as it shows off the array of peltier coolers quite well. You will also see part five (radiator and recirculating pump testing) from which this image was taken.

Part four – electric stove testing

Part five – radiator and recirculation pump testing

Comments

  1. Fallen says:

    I love it. I’ve done something similar with a peltier cooler to charge a cell phone. But I never followed that project through to completion. This seems fairly well executed.

  2. erich says:

    Using latching relays or mosfets would reduce the power currently used by the relays.
    20mA at around 13volts, multiplied by three relays, is almost a watt – enough to charge a phone!

  3. Drake says:

    Either use a larger radiator or do a passive cooling setup.

  4. gannon says:

    Although cool, might a steam turbine on top of the fire running a small dc motor be more efficient?

    • SavannahLion says:

      That was exactly my thought. I can think of a number of alternate ideas better suited to powering small electrical devices. Not quite as many I would want to carry on my back in the wild. So to that, I missed something, what is his goal with this project? What’s he trying to run/charge?

      • sjamaan says:

        Yeah….I just checked an efficiency chart…not sure about the validity…but peltiers are only like 5% efficient….for use as heat pumps…compressors are like 50% (ten times better)….I am gonna have to guess that it is not too efficient…but off the grid somewhere…it is more portable than a steam engine…and could charge stuff up…even at night as long as you have a fire….would be interesting to use in a geothermal vent…or some hot springs place…but there are solar panels out putting 16V @ 35Watts close to the size as that thing…a full 50x100cm is doing about 16V @ 70Watts…

        • sjamaan says:

          I’m not complaining, though….it is a great project for discovery learning plus you can use it when your done! I wonder how much peltiers are per cm squared….high cost? heck you could use them on radiators and other things that can be passively cooled to recover some percent of energy lost through heat……

          • jordan says:

            4x4cm 150 watt (input power, not generation output) peltiers are on ebay for about $7 each. there are much better ones that are 6.2×6.2cm and are upwards of 400 watts input but $40+

            they last forever if used properly and at those prices most people can afford to give a thermoelectric project a try.

    • rue_mohr says:

      have teh water for the turbine cool the peltior! call it a hybrid!

  5. Dax says:

    Solution: insulate the hot side to moderate the amount of heat flowing through the peltiers. This can be done with something like, a small air gap between two metal plates.

    The temperature on either side of the material can be throught of as voltage, heat flow as current, and the insulating properties of the material like the electrical resistance in a circuit. Each piece of material in the path has its own resistance. Now the system can be thought of in terms of the Ohm’s law, and it can be modeled and computed as such.

    The fundamental problem is that the peltiers have thermal resistance in and of themselves, so the temperature is going to rise anyways no matter how well you cool the cold side. If you have a campfire on the hot side, it’s like trying to regulate down the voltage of a car battery to a couple hundred millivolts by shorting it through your load. If the load has some resistance, it just won’t happen.

  6. Bill Gander says:

    Love it. Love the design mostly as it looks like something you would see on a submarine or something. Easy to see and follow circuits, which is handy when you’re cranking that much juice :) Great job and hope the best on your future builds!

  7. Harvie.CZ says:

    You’ll just have to find camp with river or lake at least…

  8. George Johnson says:

    Wow. I know people that cut the borders off their maps to save a few tenths of a gram, cut their toothbrushes in half….. Good luck carrying this thing with ya out there!

    Just don’t put the elements IN the fire! Seriously, just move it away from the fire some when it’s that hot.

  9. Willaim says:

    if the fire is that hot wouldn’t thermocouples be a better idea?

  10. SteveHaD says:

    There are already special charging pans out there. They have a peltier in them and can charge a phone while boiling water. My point isn’t that he should buy rather than build but rather that it CAN be done without any flowing water. The water will only ever get to X temperature while the fire side should always be higher.

    See this video for two commercial options – http://www.youtube.com/watch?v=58b8Acjwtl4

  11. perhaps instead of a fan and radiator just pump it into a large capacity bucket. They make nice flexible 5 gallon buckets for camping that pack small, could also work well if you used the hot water from the Device to heat your shower…….

  12. tmk says:

    Heatpipes? Seems like an application for one of those If i ever saw one!

  13. arachnidster says:

    Just camp by a stream and use that for cooling. :)

  14. Scaramouche says:

    Yes, insulation and efficiency are the issues with peltiers. Mostly useful in tight spaces where a better option won’t fit.

  15. Kelvin Mead says:

    as said before, but put the unit on some large found stones, and then place them near the fire… you can control the heat by the distance to the fire.

  16. Erik L says:

    So, the pump he uses to circulate the cooling water isn’t quite sufficient to keep up, right? Still that pump uses a lot more power than the peltiers generate.
    It would be more efficient to just scrap the whole thing and power his appliance directly from mains. In fact, that would actually reduce the amount of power drawn from mains.. ;)

  17. Bogdan says:

    I wonder how much this thing weighs, just to compare with carrying batteries…

  18. Bill says:

    You don’t want to put the thermal plate directly on the heat of the fire. For a campfire device you want to use a heat-pump, a copper rod (.5″ x 8″-12″) exposed to the heat (camp fire) and attached (soldered) to your generator plate to transfer and spread the heat should deliver a better quality of heat without creating the overheating issue on the generator side. You should be able to then use heat-sinks and a small fan to hold the temperature difference rather than the water system. This is a very fun project and can be scaled up nicely. Nice design too.

  19. James says:

    I think that it’s simply too small a water volume. Needs a large “header” tank, and a larger surface area for cooling. It doesn’t need to be a closed system.

    Look at the size of the cooling water tanks for old stationary enginess etc.

  20. max says:

    using thermosyphon with a big tank should avoid the need of an electrical pump

  21. ScottyP says:

    Dude, I wish my projects were all made with that level of craftsmanship.

  22. Hitek146 says:

    Hot side getting too hot, and then the cool side is above the hot side, further taking on heat due to the fact that heat rises? Seems more logical to bury the cold side in the earth, using convection pipes as necessary, and then build the fire on top of the upward facing hot-side, possibly using a ceramic plate or something else as a slight insulator to keep the hot coals from directly contacting the hot side.

    Just a thought…

  23. Hans says:

    There is a company who makes allready use of the peltier slabs.

    http://housewares.about.com/od/heatingwithwood/gr/ecofan.htm

    I tryed to make one for my woodstove, not yet ready.

  24. neil says:

    For some reason my meter’s just shit itself ;-)

  25. greg says:

    if we could only come up with av way to run frion while still maintaining enough power to run something else

  26. greg says:

    have you tried maybe a co2 system on the cold side?

  27. paul says:

    I’m looking up stuff about the peltier’s,one of the things is that they are talking about the max. temp. difference of it,if you stay in that zone you get the max out of it.Going higher does not work. Dax says to leave a gap (insulate)between the two sides,totally agree with that.If you would make the aluminum plate on the cold side thicker,or box it to have more cooling on the surface.When you keep it a closed circuit u can use glicol coolant,but you will need a lot of surface,ore dip the radiator in a reservoir.Also when you tilt your generator you will still heat the peltier’s by the radiation flow(heat travels up) and probably put less heat in the total divice.I hope you have some use of my pondering

  28. l0rdr0ck says:

    The surface area issue. Think about a heatsink it folds over and over
    or has a complex 3d structure to maximize surface area in a give space
    for the purpose of distributing heat. The efficiency of “pelters” is a measure
    of thermal difference that the cooler can operate at. If a natural condition
    can provide a large temperature swing have at it.

    I think the more salient point is, this is a decent way to utilize
    more of the energy being consumed and essentially wasted.
    Free work energy, only in that you already accepted huge lossy systems
    in the first place.

    You already have the fire going, because you needed the fire, you didn’t build
    the fire with the purpose of electricity.

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