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willdood t1_j4l9q8r wrote

They usually have a thermoelectric module embedded in them, which generates electricity using a temperature difference over a semiconductor. The heat from the stove warms one side while the air flow from the fan cools the other. This is why they usually have some form of fin array on the top to make heat transfer to the air more efficient. The module drives an electric motor attached to the fan.

The same principle could also be applied with a Stirling engine - the temperature difference between parts of the engine can be used to produce mechanical work and drive the fan directly, without electricity.


bgraham111 t1_j4li6y3 wrote

Boom. You won't get a better, simpler answer than this.

Even tossed in the Stirling engine answer at no cost. (your fan is thermoelectric, but technically a Stirling engine would work.)


gh0stwriter88 t1_j4ll5do wrote

Actually there are probably a lot more of these with sterling engines than TECs... since that's the Amish solution. It acutally makes way more sense than running electric motors to move the heat too since you arent' wasting electricity to do something that the motion of heat can do for you.... and all the heat is going into the room anyway.


bostwickenator t1_j4lo68x wrote

The Amish aren't a huge market verses the whole planet and useful Stirling engines are difficult to build down to a price. The peltier ones are so cheap they are almost certainly more plentiful.


pm_me_good_usernames t1_j4lt0n0 wrote

Most Amish can use low voltage electricity--you'll often see them using electric calculators at markets, at least in southeast Pennsylvania.


rayfound t1_j4lzp5a wrote

Yeah the most common thing as I understand it is that they are to be "un-yoked" from modern world. Thus off grid electricity is okay, grid tie isn't. ... Varying degrees here but many also use cell phones.


severe_neuropathy t1_j4mg64h wrote

Some use electric power tools as well, as you said they mainly care about being off grid so they run generators when they need electricity.


LonelyPerceptron t1_j4mjn40 wrote

Generators that are fueled by the kerosene they make from pine sap on forests that they control, right? They don’t just buy gas/diesel from the corner store who buys it from the refinery that makes it from grid-connected power, right?


Painting_Agency t1_j4mp7o9 wrote

Trying to gotcha the Amish when you have a superficial understanding of their beliefs isn't really a useful activity.

Their society has its own sins but they believe technology shouldn't alienate people from community and their heritage. They adopt new ways cautiously and with reservation, for instance, a telephone used to sell crops or to call for aid in an emergency. Using gasoline as needed to aid farming or the household is something they have considered and in some cases accept.


pm_me_good_usernames t1_j4mp68u wrote

For at least some Amish I think the main rule is they're not allowed to enter contracts. So they can buy gas and batteries but they can't have mains electricity, they can use a phone as long as it's pay-as-you-go. I'm pretty sure that varies between groups; each Amish community basically has its own rules. I know some of them don't use electricity at all, but they can use pneumatic power tools. And there's still a fair few pay phones in Amish country they can use to call doctors and veterinarians and people like that. There's also other groups of Anabaptists like Mennonites that are similar to Amish in some ways but different in others, even some that drive cars and work in offices but just always wear long sleeves no matter the weather.


Painting_Agency t1_j4ncuve wrote

> Mennonites

There are at least a few Mennonites attending the veterinary school where I work. Women, otherwise honestly I might not have recognized them as such. They show up wearing their home sewn dresses and bonnets, and go to classes in a teaching hospital where they learn about every high-tech treatment that veterinarians now have access to.


OogoniuM t1_j4mbma3 wrote

When I worked at GameStop a decade ago, the Amish were the ONLY people buying PSP games/movies. It was and still is fascinating to me


Kraz_I t1_j4pindb wrote

Are you sure they weren’t Mennonites?


OogoniuM t1_j4piuwu wrote

They rode their horse and buggy to the stores. We have a nice sized Amish community in indiana


polygeekYYC t1_j4ovtv1 wrote

But.....don't they have to charge them?


DivideEtImpala t1_j4p8j0i wrote

Bicycle transformer? PSPs probably didn't draw more than 10W or so, so even with mechanical and electrical efficiency losses it should be more than enough.


ZeroTrousers3D t1_j4nq1vg wrote

The few Mennonites I've known have all had phones, electric lights, fridges, stoves, etc. The basic, functional stuff. One guy even kept an old laptop for doing his books.

The way it was explained to me is that modern stuff that's used to a 'good' purpose like phones for urgent communication and business, or electric refrigeration to keep food from spoiling are okay; but things meant to entertain or replace "the work of human hands" is not.


Raul_Coronado t1_j4pfxuk wrote

Theres countless variations of amish and mennonites that all have various standards, often based in interpersonal conflicts more than anything


warriorscot t1_j4phwcw wrote

It really depends on the particular definition of their group. Amish isn't a monolithic group, even most of the monolithic religions and groups aren't particularly well connected.


bgraham111 t1_j4lmegs wrote

Wait? I wasn't aware that the Amish used sterling engines. I'd love to hear more. Do you have any info on these?

Did you mean steam engine? Sterling and steam are different...

Of course, steam engines are a solution that the Amish use... I've just never heard of the Amish using high tolerance machining to build a stirring engine.


FluxD1 t1_j4m1fvw wrote

I collect and restore antique steam engines, the Amish really do love these things. Some of the best, and worst, running engines I've seen have come from Amish hands. They either meticulously take care of them, or they run them into the dirt.

Can't say that I've ever seen them use a Stirling engine, however large Stirlings are pretty rare. Wouldn't be surprised to see one in Amish country though


bgraham111 t1_j4m9v5b wrote

I grew up in Amish country (even been to an Amish wedding reception), and know they use steam engines... never a Stirling engine. But those steam engines are beautiful.

I interviewed at a company that was planning on building Stirling engines back in 2008. They told me (no idea how true) that other than little toys and novelty sterling engines, there were less than 300 large sterling engines in the world (and they wanted to produce 3000 a month). They went out of business.


Blazin_Rathalos t1_j4mavdk wrote

...What was even their business plan for making that many then?


bgraham111 t1_j4mbg0j wrote

Solar power. Use parabolic mirrors, track the sun, heat up the Stirling engine. The prototypes worked, and worked well. Better than photovoltaic cells.

The trick is manufacturing the Stirling engines, which.... is not easy.


Inutilisable t1_j4mfa65 wrote

What is tricky about the manufacturing exactly?


SacredRose t1_j4n4dfc wrote

You need to build something with as little friction as possible and it needs to run super smooth all the way around. I imagine the precision machining needed to build larger versions is gonna be pretty high and tricky so it won’t be cheap.


Inutilisable t1_j4n7mm4 wrote

I designed lab equipments with precision pistons made of graphite in glass tubes. It’s really good but it is expensive, especially in low quantities, something like >40$ for 1/2” diameter piston, a few inches long. There was no other way to get low friction. I imagine that other constraints gets involved when you want to get any useful energy from it, at large scale.


joalheagney t1_j4pb3u8 wrote

The other big issue is the driving gas. You want something with a really low molecular mass for maximum thermal expansion. Hydrogen gas would be ideal if it didn't have a distressing tendency to diffuse into and through metals. And. You know. Explode in contact with heat and Oxygen.

Helium is half as good (twice the MM) ... but incredibly expensive and almost as hard to contain. Doesn't explode though which is good.

And then you're into N2, O2 and you may as well use air for obvious reasons. At about 14 times the MW of hydrogen gas. :/


Turksarama t1_j4oxg1d wrote

I remember when people thought that solar Stirling generation might become a thing. Then the price of PVs never stopped plummeting.


ozspook t1_j4q8opp wrote

Stirling cryocoolers were quite popular for superconducting high-q microwave and mobile phone base station filters, for a while.

Pretty good 2nd hand source for making Stirling engines.


gh0stwriter88 t1_j4q34wp wrote

Yes woodstove mounted sterling engines... It's small just enough to drive a fan decently. Sterling engines don't require tight tolerances... For basic ones, you only see that in solar parabolic generators etc too eek out more power.


Wedoitforthenut t1_j4mpbsc wrote

Ironic that the Amish will allow heat to do the work for them, but no electricity. I wonder if thats just due to a lack of understanding, or if there is some principle of electricity that the Amish don't like? I am ignorant of Amish culture tbh.


MyMomSaysIAmCool t1_j4nswy9 wrote

TL/DR: They don't reject electricity or any other technology outright. They pick and choose the technology that will benefit them, and reject anything they feel is detrimental.

Long version: There's many flavors of Amish, and all follow different rules. Technology is allowed or forbidden depending on its impact on the community. Telephones? Some communities love them, it brings distant neighbors together. Cellphones? Yes, for the same reason. A smartphone that lets you spend all day scrolling Reddit, that's probably not going to fly because it'll separate you from your community rather than bringing you closer.

And there's also rules for what's allowed at work. A friend of mine bought a trailer from a PA company, and she was surprised to see Amish people driving forklifts, running power tools, arc welding, etc, as part of the manufacturing process. The Amish aren't held to the same standards when on the job, because doing so would make them unemployable.

So yeah, it's not as simple as it seems, and every community is a little different.


tribrnl t1_j4oo27j wrote

The Amish people who built the home next door to my in-laws in Iowa were able to use power tools as long as they were pneumatic. Didn't write make sense to me, but whatever. They also had a non Amish guy drive them to and from the work site in a van.


gh0stwriter88 t1_j4q2soo wrote

Its because grid electricity makes you beholden to the electric company....generators are usually ok for work use or pnumatic.


tribrnl t1_j4qhhcb wrote

Thanks, I always thought that it was about modernity or technology or something!


edjumication t1_j4nildw wrote

Actually in this case the wiring and electric motor are 100% efficient. Any energy lost will eventually end up as heat which you are trying to release into the room anyway.


dogswontsniff t1_j4n7f20 wrote

Unfortunately, the heat rising off the stove produces way more vertical force than these produce horizontal force.

It's better than nothing if you got one for free, but a simple box fan can move wood stove air at a much lower cost effective price.

Looks like r/woodstoving is leaking. We get questions about these things weekly.

Merely a neat looking gimmick


bigflamingtaco t1_j4oltp7 wrote

How is free fan operation less cost effective than paying for electricity?

I don't think many are expecting tec fans to blast air across the room. Anyone that knows anything about peltier knows you don't get a tremendous amount of power out of them for the same reason they consume a lot of power to cool anything.

Mounting one to my Big Buddy heater is a heck of a lot cheaper than supplying the internal fan with D-Cells, which can't even make it through a single weekend of camping.


joalheagney t1_j4pbw10 wrote

Because you can just allow more heat to go up a tall, well designed/balanced chimney, at a lower fuel to heat efficiency, than taking that heat, converting it to electricity, then to kinetic energy.

Same overall effect with extra (unnecessary) steps. Chemical PE -> heat (-> electricity) -> kinetic energy -> gravitational PE.

A better overall strategy is mass heater fires, like mass heater rocket stoves, or Scandinavian masonry stoves. Burn a small fire, hot, fast and about 70% efficient. Let the heat soak into a massive thermal mass and allow the heat to slowly soak out into the dwelling.

An even better solution are Chinese fire-beds, where you sleep directly on a very flat, very short stove. Heat the body, not the house.


bigflamingtaco t1_j4zxrx2 wrote

I don't think we're on the same page here. I'm talking about using a tec fan with a portable propane heater instead of using batteries to run its internal fan, not using tec fans as a solution for all heat distribution requirements. You use tec fans with Mr Heater style propane burners and micro stoves as often used for winter camping. If you're running your buck stove in the living room and want to distribute the heat to the other end of the house, tec fans aren't going to do it.


joalheagney t1_j51th4w wrote

Ah. The OP was talking about installing a stove so I was thinking like a wood stove.


bigflamingtaco t1_j5319nn wrote

Sorry, I probably should have been clearer about my transition to small heaters.


ozspook t1_j4q9iv9 wrote

I use mine to cool the base of the flue a bit, where it exits the heater, hopefully extend the life of the hottest part a few more years.


zebediah49 t1_j4ntrsm wrote

I happened to run into one of them a couple years back, and also happened to have a thermal camera on me at the time, and thought it was neat.

Temperature across a heat-powered fan on a wood stove. Note the nearly constant bottom section temperature, and a sharp 40F delta-T in the center where the thermoelectric pad is.

E: Sorry for the potato quality, but we're talking minimum budget FLIR Lepton here. And my MSX alignment is a bit off.


dinominant t1_j4o6pb8 wrote

Thanks for sharing this. I'm surprised the hot side is only 82°C. Not even hot enough to boil water. However the fan is actively cooling the fireplace, so that does explain why it isn't over 100°C.


[deleted] t1_j4ljvki wrote



noclue72 t1_j4lmkck wrote

I watched a video recently and you can change the direction the fan spins by applying heat to different parts too. Not sure if it was a stirling one or peltier.


bkinstle t1_j4lns1a wrote

Stirling engines have lots of moving parts but peltier fans just have a small white square about 4mm thick between two metal structures without why moving parts safe for the fan itself


Mikel_S t1_j4q3rti wrote

Now that this is answered so concisely, can anybody link to one of these fans? I'd like to see if we could retrofit one onto our flue.


I_love_hate_reddit t1_j4oirj0 wrote

That's also how motorhome refrigerators are kept cool with nothing but a gas flame from the propane tank


Firegardener t1_j4p07j7 wrote

Aren't those gas refrigerators using the gas to evaporate the cooling medium and so on?