Thermoelectric Fan Harvests Wood Stove Heat Junkyard Style

Anyone who heats with a wood stove knows that the experience is completely different from typical central heating. It’s not for everyone, though, and it’s certainly not without its trade-offs. One of the chief complaints is getting heat away from the stove and into other areas of the house, and many owners turn on an electric fan to circulate the heated air.

That’s hardly in the green nature of wood heating, though, and fans can be noisy. So something like this heat-powered stove-top fan can come in handy. Such fans, which use Peltier devices to power a small electric motor, are readily available commercially. [bongodrummer] thought that sounded like no fun, though, and created his own mostly from junk. The Peltier module was salvaged from an old travel fridge and mounted to a heat sink from a computer to harvest heat from the stove. The other side of the Peltier needs to have a heat sink to keep it cooler than the hot side, and [bongodrummer] chose an unconventional bit of salvage for the job — the cylinder of a chainsaw engine. The spark plug hole sprouts the mount for the fan motor, and the cooling fins help keep the Peltier cool. And to prevent overheating of the device, he added a surprise — a car cooling system thermostat to physically lift the device off the stove when it gets too hot. Genius!

The video below shows the build, which was not trivial. But we think the end results are worth it, and it reminds us a little of the woodstove generator we featured a while back.

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Thermoelectric Generator Shines Where the Sun Doesn’t

For off-grid renewable electricity, solar seems to make sense. Just throw some PV panels on the roof and you’re all set to stick it to the man, right? But the dirty little secret of the king of clean energy is that very few places on the planet get the sort of sunshine needed to make residential PV panels worth their installation cost in the short term, and the long-term value proposition isn’t very good either.

The drearier places on the planet might benefit from this high-power thermoelectric generator (TEG) developed and tested by [TegwynTwmffat] for use on a wood burning stove. The TEG modules [Tegwyn] used are commercially available and rated at 14.4 volts and 20 watts each. He wisely started his experiments with a single module; the video below shows the development of that prototype. The bulk of the work with TEGs is keeping the cold side of the module at a low enough temperature for decent performance, since the modules work better the higher the difference in temperature is across the module. A finned heatsink and a fan wouldn’t cut it for this application, so a water-cooled block was built to pump away the heat. A successful test led to scaling the generator up to 10 modules with a very impressive heatsink, which produced about 120 watts. Pretty good, but we wonder if some easy gains in performance would have come from using heat sink compound on the module surfaces.

Using thermal differences to generate electricity is nothing new, but a twist on the technique is getting attention lately as a potential clean energy source. And who knows? Maybe [TegwynTwmffat]’s or one of the other Hackaday Prize 2018 entries will break new ground and change the world. What’s your big idea?

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Thermoelectric Paint Opens Prospect Of Easier Energy Harvesting

We will all be used to the thermoelectric effect in our electronic devices. The property of a junction of dissimilar conductors to either generate electricity from a difference in temperature (the Seebeck effect), or heating or cooling the junction (the Peltier effect). Every time we use a thermocouple or one of those mini beer fridges, we’re taking advantage of it.

Practical commercial thermoelectric arrays take the form of a grid of semiconductor junctions wired in series, with a cold side and a hot side. For a Peltier array the cold side drops in temperature and the hot side rises in response to applied electric current, while for a Seebeck array a current is generated in response to temperature difference between the two sides. They have several disadvantages though; they are not cheap, they are of a limited size, they can only be attached to flat surfaces, and they are only as good as their thermal bond can be made.

Researchers in Korea have produced an interesting development in this field that may offer significant improvements over the modules, they have published a paper describing a thermoelectric compound which can be painted on to a surface. The paint contains particles of bismuth telluride (Bi2Te3), and an energy density of up to 4mW per square centimetre is claimed.

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Thermoelectric Dry Ice Generator Does Not Work (Yet)

[Pabr] is trying to make dry ice the hard way by building a thermoelectric dry ice generator. The project is a well planned round trip through thermodynamics and cryogenics with a hard landing on the icy grounds of trial and error.

[Pabr’s] four stage Peltier element on a heatsink.
While dry ice can be obtained with simpler methods, for example by venting gaseous CO2 from fire extinguishers and collecting the forming CO2 flakes, [pabr’s] method is indeed attractive as a more compact solid-state solution. The setup employs a four stage Peltier element, which uses four Peltier stages to achieve a high temperature differential. With sufficient cooling on the high-temperature side of the element, it should be well capable of achieving temperatures below -78.5 °C, the sublimation temperature of CO2. So far, [pabr] has built three different setups to expose small amounts of CO2 to the cold of the Peltier element, hoping to observe the formation of little dry ice flakes.

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I am a Battery: Harvesting Heat Energy

If you get tired of charging batteries, you might be interested in [Hackarobot’s] energy harvesting demo. He uses a peltier device (although he’s really using it as a thermocouple which it is). A 1 farad super capacitor stores energy and an LTC3108 ultra low voltage converter with a 1:100 ratio transformer handles the conversion to a useful voltage.

The truth is, the amount of energy harvested is probably pretty small–he didn’t really characterize it other than to light an LED. In addition, we wondered if a proper thermocouple would work better (some old Russian radios used thermocouples either in fireplaces or kerosene lamps to avoid requiring batteries). Although a Peltier device and a thermocouple both use the Seebeck effect, they are optimized for different purposes. Thermocouples generate voltage from a temperature differential and Peltier modules generate temperature differentials from voltage.

However, as [Hackarobot] points out, the same technique might be useful with other alternate power sources like solar cells or other small generators. The module used has selectable output voltages ranging from 2.35V to 5V.

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Building Your Own Mini Fridge?

Ever play with a Peltier plate? They’re these really cool components that kind of look like a ceramic sandwich, and when you put power into them, one side gets hot, and one side gets freezing cold! [Joseph Rautenbach] decided he wanted to try making his own mini fridge out of one — which is typically how most modern mini fridges work these days.

The peltier plate he’s using draws 12v at about 3.5 amps — so about 50W — and if you don’t heat sink it properly you could burn it out in a matter of seconds. Peltier plates only care about the temperature differential between the two sides — if you don’t take the heat away from the hot side, it will soon overheat and destroy itself.

[Joe’s] using a styrofoam cooler for the fridge with a pair of computer heat sinks and fans for the peltier plate, and a temperature PID controller he bought off eBay. The external heat sink sucks away the excess heat generated by the peltier plate, and the internal one helps spread cooled air around the inside of the styrofoam cooler. The PID controller allows him to set a preferred temperature to maintain in the box, which will then control the outputs to keep it that way.

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Wrapping Up The Last Midwest RepRap Festival

The Midwest RepRap Festival is over – forever. This was the last one. Apparently enough people complained that Goshen, Indiana wasn’t in the midwest. The number of Dairy Queens I passed contradicts this, but whatever. Next year, there’s going to be a different con in Goshen. Same content, different name. If you have a suggestion, you know where to put it.

I promised the world’s largest 3D printed trash can, and I gave you the world’s largest 3D printed trash can. This gigantic orange vase was printed on the PartDaddy, SeeMeCNC’s 18-foot tall delta printer a few months ago at the NYC Maker Faire. I have been using this as a trash can in my basement since then, making me one of the only people who have their trash can on Wikipedia.

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A failed print on Saturday morning

Speaking of the PartDaddy, this is what a fail looks like. The first PartDaddy print was a Groot, a 13-hour long print job. It was left running overnight, but it ran out of PLA pellets sometime around 4 in the morning. If you’re wondering what the black band is around the Groot’s face is, here’s the breakdown:

The PartDaddy sucks PLA pellets up from a trash can (that’s not 3D printed), and dispenses it into a hopper above the print head. This hopper was 3D printed on the PartDaddy, and there is still a little bit of colarant dust in there. When the PLA pellets run out, that dust is embedded in the extrusion. When you realize that masterbatch is only about 5% of the finished plastic, it doesn’t take much black dust to discolor a print.

Yes, this is a print fail that could have been fixed by having an all-night bash. A few other people left their printers running overnight including [The Great Fredini] and his Scan-A-Rama. This was a Rostock Max that had something wonky happen with the Bowden. There was filament everywhere.

How about some Star Wars droids? An R2 from the Droid Builder’s Club was there, but there was also the beginnings of a completely 3D printed Roger. While we’re on the subject of plastic robots that will fall apart at a moment’s notice, there was a K’NEX 3D printer. Yes, it’s made almost entirely out of K’NEX, and it did work at one time. Those orange parts sitting next to it? Those came out of the K’NEX printer.  If you’re looking for the definitive RepStrap, there ‘ya go.

 

NEW FILAMENTS

For the last few months, metal filaments – PLA with tiny particles of copper, brass, bronze, iron, or aluminum have been available. MRRF was the first place where you could see them all together. A few things of note: these filaments are heavy – the printed objects actually feel like they’re made out of metal. They’re actually metal, too: the iron-based filaments had a tiny bit of red corrosion, and the Lincoln death mask above was treated with acetic acid. These filaments are also expensive, around $100 for 1kg. Still, if you want to print something that will be around in 100 years, this is what you should get.

The most beautiful printer ever

MRRF should have had a contest for the best looking 3D printer at the show. A beautiful delta from Detroit Rock City would have won:

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DSC_0075That white hexagon in the center is a ceramic PCB that I’m told cost an ungodly amount of money. Underneath the ceramic build plate, there’s a few Peltiers between the bed and the large copper heat sink. The heat sink is connected to the three risers by heat pipes, making the entire printer one gigantic heat sink. Why would anyone make such an amazing art deco printer? For this.

Because you can use Peltiers to heat and cool a bed, a little bit of GCode at the end of a print will cool the bed to below room temperature. If you do your design right, this means the print will just fall over when it’s done. When the print bed is cooling, you can actually hear the bond between the bed and print cracking. It’s beautiful, it’s cool, and I’m told this printer will make its way to hackaday.io soon.


There you go, the best and coolest from the last Midwest RepRap Festival ever. There will never be another one. It only needs a better name, and [John] at SeeMeCNC is great at coming up with names. Just ask what VIP is a backronym of.

I told you there would be a T-shirt cannon. That’s 300 PSI shop air.