So I bought an EcoFan for a friend and decided that it was a cool concept and built one from scratch. The fan gets its power from a peltier element that is used in reverse, i.e. it is generating electricity from the heat given off from the stove top.
This peltier cooler is used in cooling cpus to tabletop wine coolers. Usually electricity is used to generate the peltier effect and causes one side to cool while the other side heats up. More can be found on the wikipedia article on http://en.wikipedia.org/wiki/Thermoelectric_cooling
I always wanted to build a Stirling engine but the complexity was a little too much for me, but this project was easily doable as a weekend project!
C-clamps (or vice grips)
1x 120cm CPU Heatsink ($20 shipped internet)
1x Peltier ($30 shipped ebay)
1x 1.5V Radio Shack hobby motor ($3)
1x Pentium II heatsink (salvaged)
1x 6" propeller (from my RC planes)
1x scrap 1/8" aluminium plate
6x nuts and bolts
It's relatively easy to build. I just sourced the cheapest and largest heatsink on the internet, which came to this 120cm massive heatsink for $20 shipped. It included all the right mounting plates that just worked. It had a mounting plate that was wide, came with a whole bunch of screws to mount it too. WIthout this it would have made it a whole lot harder to mount.
The $30 thermoelectric generator was sourced from ebay through a local vendor (because I was impatient and wanted to build it by the weekend). I also bought the high temp version, which raised the price considerably (which I have found isn't quite necessary as the module never gets that hot enough). So, if you're more patient, these can be sourced through ebay from chinese vendors for under $15.
The electric generated from the module is roughly about 1.5-3v. Not a whole lot of power, so Radio Shack to the rescue! Got a hobby motor for $3. And using a salvaged propeller from one of my rc aeroplanes, I managed to push fit it into the Radio Shack motor.
The base plate is a 1/8" aluminium plate I found and I used a hacksaw to cut out the pieces, then file away the edges.
There's no plans for it because it's basically lining up the holes, clamp it down, drill the holes out (although it helped that I had a Bridgeport mill, I could have just easily used a hand drill). Also I wanted to make it in such a way you can have a margin of error. I suppose you could also tap the holes and bolt it right on, but I wanted to keep it simple to build.
I made a little base and riser for the motor so it sits more centrally on the top heatsink and just ziptied it up.
The fan base heatsink is a Pentium II heatsink that I had laying around. The heatsink also does two things, one is that it raises up the height, and second is to reduce the temperature getting to the peltier module (because I wasn't sure how well it could dissipate the heat)
After the first run, I could touch the top of the heatsink and only felt that it was slightly warm. This fan works better than the EcoFan in the fact that it dissipates the heat better and can be put up front on the stove without losing too much efficiency.
All in all, about a couple hours of work!
So have fun building your own!