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OT, How does this fan work? Any ideas?

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  • #31
    Interesting experiment anyone can do with those devices- I scrounged one from a wine cooler and hooked up some juice to it. As predicted it got hot on one side and cold on the other. I then clipped a small motor to the leads and watched it run. Dipping the cold side into cold water boosted the rpm a bit during the wind-down stage once the cold side had started to warm up. It acted like an energy storage device- but very inefficiently. It was fun for awhile to play with.
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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    • #32
      Originally posted by Franz© View Post
      Soviets were doing the thermocouple in a kerosene lamp back in the early 60s so remote villages could power a transistor radio with it.
      As I recall they used iron and copper wires brazed together at the flame end and soldered at the outside, 2 decks high.

      My personal attempt produced very little power, burned fingers and a broken lamp shade. Never got sufficient voltage to run the 9 volt transistor radio.
      If memory serves it was in Popular Science or Popular Mechanics.
      Not sure if this was the thing you had read but it sounds similar. From a 1960 edition of Modern Mechanix magazine:

      http://blog.modernmechanix.com/keros...-powers-radio/

      And a slightly more comprehensive write up indicates this was operating a tube radio with a vibrator power supply. Read it here on page 37:

      https://www.americanradiohistory.com...-1958-08-R.pdf






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      • #33
        Originally posted by Franz© View Post
        Soviets were doing the thermocouple in a kerosene lamp back in the early 60s so remote villages could power a transistor radio with it.
        As I recall they used iron and copper wires brazed together at the flame end and soldered at the outside, 2 decks high.
        Yes, somewhere I have a russian book (translated) about that, and attempts to do refrigeration that way also, putting current through. As I recall, it was "still under development", likely meaning that it "worked", but not well enough.
        1601

        Keep eye on ball.
        Hashim Khan

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        • #34
          Originally posted by Franz© View Post
          Soviets were doing the thermocouple in a kerosene lamp back in the early 60s so remote villages could power a transistor radio with it.
          As I recall they used iron and copper wires brazed together at the flame end and soldered at the outside, 2 decks high..
          I remember reading an article about those in one of the magazines I use to get when I was working for an electronics place back in the 60s . I was impressed at the time. I think that was before Peltier an Seebeck were born. :-)
          ...lew...

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          • #35
            I was studying this topic of Peltiers and thermocouples wondering what it would take to get a charge on a cell phone off the grid. It seemed to be a reach, the wattage on the thermocouple is so low, and the Peltier so temp sensitive. The only way with the Peltier is using it on top of a pot of water that moderates the temp to <212, but then cooling the other side is pretty tricky. That brings in heat pipes, and then it goes full Rube Goldberg!
            Location: Jersey City NJ USA

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            • #36
              I have that exact model spinning away on my woodstove even as we speak. They don't move a lot of air but are dead quiet and work when the power is out. When the built-in blower on the stove is running (very effective, but NOISY), it cools the outer skin of the stove enough that the Eco-Fan nearly stops.
              It's all mind over matter.
              If you don't mind, it don't matter.

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              • #37
                You can get little drink coolers to go in the car which plug into the lighter socket which run using peltiers, with a finned radiator. That's because peltiers work both ways.

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                • #38
                  From what I have found, the maximum temperature for a Peltier or Seebeck module is 200C (392F), and for some this may be as little as 80C(176F), although that may be the difference between hot and cold plates. From my experiment, it seemed to be practical to have the hot plate on the woodstove surface, and the cool plate with a heat sink and ambient air blowing over it. But the stove surface can get much hotter than 200C, so that will need to be controlled. I was able to get nearly 2 volts before failure, so probably 1 - 1.5 volts would be reasonable. Four modules in series would be able to produce 4 -6 volts, which is plenty to charge a cell phone that usually takes USB voltage nominally 5 volts but perhaps as low as 3.

                  Here are some temperature readings for the stove:

                  Stack...Surface
                  250F....163C....Lower Corner
                  200F....147C
                  190F....132C
                  200F....140C
                  300F....129C
                  300F....165C....Lower Middle
                  200F....108C....Upper Corner
                  300F....109C
                  300F....131C....Upper Middle
                  290F....124C
                  160F.... 90C
                  Last edited by PStechPaul; 01-18-2020, 08:57 PM.
                  http://pauleschoen.com/pix/PM08_P76_P54.png
                  Paul , P S Technology, Inc. and MrTibbs
                  USA Maryland 21030

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                  • #39
                    I bought some of those modules when they were 'cheap'- only about $10 each. Long time ago. Now you can get them cheap, and they are probably better. It seems likely that the limiting factors are the melting point of bismuth, which is very low, and soldering temps where all the little bits of 'active material' are put in series. But the whole thing there is getting the temperature differential going on. For a stove top unit, the 'cool' side is still going to be pretty warm- unless you arrange to cool that side with a cold water flow for instance.

                    It used to be that you would find a water jacket on the back of wood stoves- that was a way to get hot water, but it also seems to me a way to get a thermocouple stack going on. Make the water jacket in two pieces and sandwich the modules between them. The 'inner' jacket is heated by the back of the stove, and the outer jacket has cold water piped in. The exit from the cold jacket feeds the input of the hot jacket, and as long as you periodically take hot water out, the cold side will remain closer to the temperature of the incoming water. There might be an optimum rate at which you allow water through the system so the hot side can actually reach something near boiling point, and the cold side gets enough fresh water to keep it cool.

                    Because the heat would be there anyway, the efficiency issue is a moot point. Whatever power you get from it is a bonus that you didn't have before, so as long as it is a useful amount to run a fan or charge a battery, you're good. Using these modules in the traditional way, to run a cooler, you have to throw away a lot of heat- which comes from burning fuel in a vehicle, so it does become an issue. These things usually have a fan to blow away the heat, but the hot side is still hot- which means that the cool side is limited to how cool it can become. I've toyed with ways of getting the hot side as cool as possible- like making the outside of the cooler from aluminum sheet to conduct the heat into a large area where it can be radiated from, instead of into a smaller area (the heat sink) where you have to blow the heat away. Another way to do it would be to use some kind of water jacket on the hot side, and you periodically replenish the cool water. If you were to keep the heat sink at the temperature of lake water for instance, the cold side would become cold enough to freeze- or to allow you to keep the contents of the cooler cool enough with less energy usage.

                    In any event, you are not limited to placing a module on top of your wood stove in order to gain enough energy to run a fan. This seems about the most inefficient way to use the modules. I like the hot and cold water jacket idea. Another possibility with it is to cool the cold side with incoming air which then goes to feed the stove. As the stove burns it will create a constant flow of air, so this idea seems feasible.
                    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                    • #40
                      I edited my post #38 above with some stove surface temperatures. Just now I put one of these modules on the stove with temperature of 128C, and I got 500 mV into a 1.8 ohm resistor, which is 270 mA and 135 mW. The module has about 2.5 ohms resistance which matches its 5 amp nominal current draw at 12 volts. And this would mean its open circuit output at 128C would be about 1.16 volts. For cold plate temperature of 28C this becomes 11.6 mV/degC. So four of these could produce 4.6 volts open circuit or 2.3 volts into 5 ohms for maximum power of a little over 1 watt (250 mW/module).
                      http://pauleschoen.com/pix/PM08_P76_P54.png
                      Paul , P S Technology, Inc. and MrTibbs
                      USA Maryland 21030

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                      • #41
                        it is a thermoelectric device, a piece of extrusion, an injection molded prop, and a $0.42 mabuchi brushed motor. certainly not worth $99
                        -paul

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                        • #42
                          Bet you can't build one like it for less than $100, if you consider your time is worth $25/hr. And you'd have to make them for less than about $25 each to sell them at $99 retail. They'd be available for $10 each if the Chinese could sell millions of them, but it's a pretty narrow market niche. The thermolectric unit may be somewhat special to avoid overheating and failure on a hot woodstove.
                          http://pauleschoen.com/pix/PM08_P76_P54.png
                          Paul , P S Technology, Inc. and MrTibbs
                          USA Maryland 21030

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