Some months ago, while browsing Instructables I came across a post by Joohansson (http://www.instructables.com/member/Joohansson/) showing how he had used the thermo-electric Peltier effect to power a fan with a small candle. Subsequently he has also shown how to use a similar device to make a phone charger. A similar project was posted more recently (http://www.instructables.com/id/DIY-Stove-Fan-for-under-50/) and both of these posts give some of the theoretical background as well as useful links for such Peltier devices.In essence, Peltier devices are thermo-electric couples which, when powered, produce cooling, for use in things like wine fridges, or when used in reverse across a heat differential, can generate electricity. By placing a simple, store-bought Peltier element between a heated heatsink and a second, heat-dissipating sink, enough electricity can be generated to run a small motor, which can then turn a fan.
I was particularly attracted by the aesthetics of Joohansson's creation and decided to make my own from scratch, using only the central Peltier element and a motor which I bought on e-bay, plus a single aluminium heatsink, as my starting point. Every other component was made from re-purposed bits and pieces from the scrapyard or my boxes of gleaned finds and left-overs. I also wanted to make the device functional, so I decided to use the fan to help distribute air-freshener.
I have not given a step-by-step guide so much as a "show and tell" because the details of what one makes in these sorts of projects is so dependent on what you have available.
Step 1: Materials and Methods
For this project I bought the following 2 components
1. Mabuchi RF-500TB "Solar Motor" (0.5 -1.5V, 380-1280 rpm). Approximately U.S.$10.00 on e-Bay
2. An off-the-shelf thermo-electric (Peltier) module (68W). Approximately u.S.$20.00 from Jaycar electronics.
An aluminium heatsink was harvested from an old computer and all the other components were made up from recycled copper piping, brass stock, brass wire and some leftover rosewood.
The heatsink which forms the cooling side of the device was made from a solid brass gas distributor, to which were fixed 3 segments of a copper heating-exchange element from a truck radiator. As long as there is good contact between the heating element, the lower heatsink, the Peltier unit and the cooling heatsink, the device will transfer heat and will generate electricity and hence, work. The rest is aesthetics and doing whatever takes your fancy. Note that to make the heat transference better, the opposing faces of the heating and cooling sinks should be well polished and the contact between the Peltier unit and the heatsinks augmented by a good layer of thermal conducting paste, available online or from electronics component suppliers.
Step 2: Candle-power
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The heat for the device comes from a simple tea-light candle, placed in a holder beneath the lower heatsink. I have used a turntable arrangement with a detachable chimney, for ease of getting at and lighting the candle and to help direct the heat. When designing this aspect of your device, don't put the candle too close to the heatsink or soot might be deposited. When firing up my unit, I use a small blowtorch ( the sort that you might have in your kitchen for creme brulee making), to light the candle and to hurry the process along a bit, by initiating and accelerating the heating of the base heatsink.
Step 3: Thermal Transfer and the cooling heat sink.
This is the centre and heart of the device. I have used an aluminium heatsink to supply heat and interposed a Peltier thermo-coupling device, with plenty of thermal paste between the polished top surface of this lower heatsink and the polished base of my home-made cooling heatsink. To make the latter, I started with a chunky block of brass, which had originally been a 4-way gas distribution hub, I think. The surface had 4 large holes bored into it, each about 1/2" in diameter and leading out into one of the four outlet arms on the sides ofd the distributor. Into these 1/2 inch holes, I placed copper piping and as luck would have it, the outside diameter of these copper pipes just fitted into the centre of the heat-exchange cores from the old truck radiator. I simply cut the cores down to an appropriate length and placed them over the copper pipes which I soldered to the brass base. Each central copper pipe carried a further coil of very fine copper tubing, all designed to help wick heat away from the brass base-plate as efficiently as possible.
Step 4: Fan and Motor mounting and housing
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The motor could have been mounted with something as simple as a nylon strap but I wanted to stick with the brass and copper aesthetic, so I fashioned a mounting using brass stock and an old brass hose clamp. The electric wires were brought through copper tubing and the joints covered with heatshrink. The wire junctions were covered with a box cover made from a piece of old brass sheeting and screwed down onto the wooden mounting block.
Likewise, the propeller could have been a hobby-shop modeller's plastic one, but I chose to cut one out of an old brass plate I had lying around. Then I soldered a bush, salvaged from an old clock, to the plate and fitted this to the shaft of the motor, locking it with a grub screw.
Step 5: Fragrance Dispenser
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With the fan mounted and the electrical connections made, the unit was tested and found to function well. In other words, the fan turned. (I have fairly low expectations in these sort of "make-it-up-as-you-go-along" projects, you can tell), So, if there's a fan, there must be airflow, and that makes it feasible to waft a bit of fragrance around. Accordingly, a brass and copper bowl was devised and mounted on the front of the motor mount so that a room fragrance or essential aromatic oil or similar, would, when dispensed into the bowl, as it evaporated, be in the airstream from the fan and would therefore be dragged into the fan's air current for distribution around the room. As desired, so it turned out - seems to work quite nicely too.