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anyone know about bi-metal electricity?
By dudevato, Section Homebrewed Electricity Posted on Wed Jan 19th, 2005 at 02:09:06 AM MST
I saw this fan at a wood stove store, it sat on top of a hot stove and spun..................

The guy said it makes a small amount of electricity from two different metals, which it feeds to a very small motor (the dia. of a quarter and 1" tall) The blade attached to it(4" dia) made Very little wind, but it sure got my attention. He said it went for $100 (not a misprint and I heard him correctly) So I did a search on google for 'bi metal electricity' and nothing came up that was what I was after. Soooooooooooo I figure this is the place to get some info on this. Anybody know anything about it? Thanks

anyone know about bi-metal electricity? | 12 comments (12 topical, 0 editorial)

Re: anyone know about bi-metal electricity? (3.00 / 0) (#1)
by picmacmillan (rmacmill@sympatico.ca) on Tue Jan 18th, 2005 at 07:14:11 PM MST
(User Info) http:// www.frecklefarmloghomes.com

hi dudeveto....ya this fan runs on the peltier effect....i have a picture of one and i will try and post it here

they work really well and are a good conversation piece...i found you have to be carefull on how much heat you put to them as they will burn out at too high a temperature....they are made in wiarton ont. i forget there name but i have it here somewhere...anyhow take care...pickster
http://www.frecklefarmloghomes.com

Re: anyone know about bi-metal electricity? (3.00 / 0) (#2)
by pyrocasto (pyrocasto at hotmail dot com) on Wed Jan 19th, 2005 at 12:32:07 AM MST
(User Info)

Yeah, I would like to know where you could get one. Even if they dont put out that much, it some. My stove has to burn for more than an hour before the thermostat kicks on and blows, so this could be a little handy.

Re: anyone know about bi-metal electricity? (3.00 / 0) (#3)
by robertfsix on Wed Jan 19th, 2005 at 03:18:17 AM MST
(User Info)

Yes electronics hobby shops (maybe even Radio Shack) will have them. Also
you can look on eBay. The key thing to search for is "Peltier".

Note Peltier devices are the heart of those 12volt small fridges you power from
your car cigarette lighter.

Put electricity in - you get a temperature differential between the two sides.

Put a temperature difference between the two sides - you get electricity.

Re: anyone know about bi-metal electricity? (3.00 / 0) (#4)
by finnsawyer on Wed Jan 19th, 2005 at 09:05:04 AM MST
(User Info)

Try "bimetal junction". It'll at least get you started.
GeoM

Re: anyone know about bi-metal electricity? (3.00 / 0) (#5)
by pyrocasto (pyrocasto at hotmail dot com) on Wed Jan 19th, 2005 at 10:50:42 AM MST
(User Info)

So I can take a "thermoelectric chip" mount it to a heat sink, and the other end to the stove? Use the fan to blow the heat?

seebeck effect (3.00 / 0) (#6)
by JW on Wed Jan 19th, 2005 at 12:18:02 PM MST
(User Info)

dudevato,

This is also called the "Seebeck Effect", as well as pelter junction. Basically pelter junctions were designed to cool things with a dc input voltage/current. Generally pelter junctions use a bismuth/tin alloying scheme to produce the junction. I am not sure if a Seebeck junction can be reversed to provide cooling, but probably does. The Seebeck juctions that I have studied, use "constant-eenn"(copper/nickel alloy) and iron or steel to make the junction. The copper/nickel too- steel junction, can handle much higher temperatures than a pelter unit, and also is not optimized to cool anything, like a pelter juction can.

JW

[ Parent ]

thermoelectric modules (3.00 / 0) (#7)
by DanG on Wed Jan 19th, 2005 at 12:18:09 PM MST
(User Info)

Bi-metal refers to disimilar sheet metal bonded together so when heated they expand at different rates so bending thin sheet metal. The heated bi-metal piece has memory and returns to original position when cooled. The stovetop fan has a built in bi-metal strip that acts to limit heat entering the aluminum base by rocking it back to reduce contact & make an air gap. The power generator is a peltier module that will be ruined if it gets diectly connected to the energy ~700F+ stovetops are releasing.

The peltier effect materials are engineered for a certain temperature range - the consumer grade stuff that's easy and relatively inexpensive to purchase will not take the high temperatures needed for stovetop use directly - there has to be a disconnect like the bi-metal strip. I've seen much higher temp peltier devices on the web for 3-5x the going rate of the common ones.

I spent a few days back east w/ my Parents and guess what, Dad got one of the two-blade 100cfm fans as a gift. He also got a digital IR thermometer w/ the laser pointer built in so I scanned the temps on the fan. The fan sat on a steel plate fireplace insert stove top - the center would heat to ~500 easily but the fan has to have cooler air to draw in to the top fins for best results so it's kept to the side of the stove top.
So with the fan base set on stovetop at ~400 the bi-metal strip would have it tilted back about 2-3mm & the aluminum fan frame would register around ~200 just below the peltier module and ~180 just above. The usual temperature drop was around ~18F but at start-up the fan would be moving with as little as 2~F difference. When it was really spinning the top fins could read between ~90 and ~135. I didn't take notes so the figures are from memory but it explains the heat flow a little better...

The design has a US Patent, I haven't researched to find what aspect of the fan won a Patent but its a really keen product. We added pyrex bread pans around it to hold water and the fan's circulation almost doubled the rate of evaporation to help keep the house comfortable.

Re: anyone know about bi-metal electricity? (3.00 / 0) (#8)
by hobot on Wed Jan 19th, 2005 at 02:37:18 PM MST
(User Info)

Look up thermocouple or thermopile, using dissimilar metals
with a temperature differences form hot connectors to cooler load
ends of the wires will generate electricy directly, similar to
solar cell w/o any mechanical effects involved. I saw a propane
compact commerical version just comming on market priot to y2k days.
There are site to explain and hobbists experimenters make em at home.
Each wire pair adds its little share so gangs of them in various
geometery are used to get usable watts out. Pickeing the metals to
fit the temerature available and not melt or corrode away is an issue.

On a side note when the chineese and others devoloped metal pins they
began electro acupuncture era as the temperature difference in the
shaft to the different metal wrapped as handle up in the air creates a
pontential with an air ion return path that is on same scale as the
firing of nerves and cellular metabolisom which is similar to the
currents of corrision or in our battery cells.

Space craft to industry use thermopiles to recover power from waste heat.

hobot

Re: anyone know about bi-metal electricity? (3.00 / 0) (#9)
by alcul8r (rex @t kansaswind Dot com) on Thu Jan 20th, 2005 at 08:05:28 AM MST
(User Info) http://kansaswind.com

Look for Peltier junctions at

http://allelectronics.com/

For about 15$ they have a whole block of them. Don't know what voltage it will put out, so don't know what kind of fan to put with it. Make sure you put it so that the fan is pulling cooler air over the heat sink, otherwise you might melt the Peltier elements.

It will also run on Ice cubes in the summer.
alcul8r KansasWind.com

Re: anyone know about bi-metal electricity? (3.00 / 0) (#10)
by wooferhound (tim((NoSpamAt))wooferhound.com) on Sat Jan 22nd, 2005 at 10:41:59 AM MST
(User Info) http://wooferhound.com

Better to search on "thermopile" which are clusters of thermocouples in one unit.
Or here are some excellent Links...

http://www.thermonamic.com/Pspec.html

http://www.varmaraf.is/engl/prod.htm

http://www.powerchips.gi/

http://www.dts-generator.com/

http://www.hi-z.com/

http://www.remote-site.com/thermo.html

)}=- W o o f -={(

Re: anyone know about bi-metal electricity? (3.00 / 0) (#11)
by ghurd on Sat Jan 22nd, 2005 at 07:17:19 PM MST
(User Info)

Picmacmillan's fan has another bi-metallic feature. Self regulation.
These things fry if they get too hot. The base plate is 2 layers of different metals. The top one expands more with heat. When the stove gets almost too hot, the top layer expands more than the bottom layer, bending it to an arc, reducing the surface area in contsct with the stove, letting the peltier cool some.

It is not fool proof. They fry regularly on red hot stoves.

Most I see are about an 8" blade.

I know of another made mostly of wood that is a Sterling. Wish I had a pic.

G-

Re: anyone know about bi-metal electricity? (3.00 / 0) (#12)
by BoneHead on Wed Jan 26th, 2005 at 11:27:30 AM MST
(User Info)

Oh yeah. Some good info here. You can do a search for "thermoelectric generator" too. Lighthouses used to use them to power the old bulbs. The Meir space station uses them too. Of course, those big boys use radioactive materials to power theirs.

anyone know about bi-metal electricity? | 12 comments (12 topical, 0 editorial)

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