Thermoelectric Power

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Biggkidd

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Has anyone here played with thermoelectric power or even seen it in use? I recently bought one of those wood stove fans that's powered by the heat of the stove. It not only works but it works better than I thought it would. I'm not saying it makes a big difference in the way the stove heats the room because it doesn't make a big change. But it impresses me in the fact that it takes heat from the stove and using the difference between the stove temp and the air temp it makes electricity to power the fan. Which has me wondering if all of us using woodstoves for heat in the winter aren't missing some free power. Why couldn't we be making some useful power from that heat?
 
"
When operated as a generator, one side of the device is heated to a temperature greater than the other side, and as a result, a difference in voltage will build up between the two sides (the Seebeck effect). However, a well-designed Peltier cooler will be a mediocre thermoelectric generator and vice versa, due to different design and packaging requirements
"

https://en.wikipedia.org/wiki/Thermoelectric_cooling
It depends on heat dlux moving from a heat source to a heat sink. The complications usually end up on the sink side when it heats up the flux is reduced. If you can keep the sink from heating up you got something.

Sterling engines have a similar challenge.

Ben
 
"
When operated as a generator, one side of the device is heated to a temperature greater than the other side, and as a result, a difference in voltage will build up between the two sides (the Seebeck effect). However, a well-designed Peltier cooler will be a mediocre thermoelectric generator and vice versa, due to different design and packaging requirements
"

https://en.wikipedia.org/wiki/Thermoelectric_cooling
It depends on heat dlux moving from a heat source to a heat sink. The complications usually end up on the sink side when it heats up the flux is reduced. If you can keep the sink from heating up you got something.

Sterling engines have a similar challenge.

Ben
Well we are already running the heat in winter. If we were to use a larger fan to keep the cool side cool then why couldn't we reap some of the power produced over what the fan uses?
 
@Neb I wonder if they could be hooked in series to produce a higher / more useful voltage?

I ordered a couple TEG's and TEC's to play with but I didn't realize when I ordered they will not be here until late spring. Oops!
 
What started me down this road was wondering if I could use one to power a micro water pump to move water for infloor heating. Now that I know the greater the temperature change between one side and the other the more certain I am I can use it to move water and possibly make some useful power.
 
TEGs work when you have a lot of High Quality Heat (>>200F) and a cold source (As @ned pointed out they rely on heat flux or temperature movement from hot to cold), I have seen them used in a number of application including on vehicle exhaust systems, but they don't produce a lot of power. Back in 2004-2011 a TEG on a GM Full Size pickup exhaust system only produced about 500 watts. They are great for moving air around a wood stove and they could be used to provide a little back-up power for phones and such. But they are expensive and designing a good operational system can be complicated.

All the being said, TEGs are neat things, applying a voltage across them can produced either hot or cold. In heating they are more efficient than resistance heating. On electric vehicle they could be used to provide occupant heating and cooling along with thermal management of the battery pack. The Chinese have shown that hybrid systems using a heat pump and TEGs could expand the range and improve the heat pumps performance at temperature extremes.

@Biggkidd, if you are moving cool water, you could use that water as a cold source and the fireplace as the heat source you could do okay. But you would need to use a low power pump....
 
Thanks Urbanhunter.

A little time on YT brought me this. Which yes it shows me I can use one to move water and I do have some very low draw pumps 12V at less than 1 amp IIRC. Which also tells me they could make some power in winter using a small radiator outside and the stove inside.
 
See how much of that stove top in the video is open and he has a 45W generator on there? Well imagine if you had designed a system for the purpose of making power and heat and used all that surface area. I see the potential for a good bit of power production without the loss of any valuable heat. I can see the possibility of making 500+ watts when your heating your home with a purpose built system! Now wouldn't that be cool? Oh I can not wait to get my hands on some parts to make a prototype!
 
Somebody has already done it!


That control box accessory should be built in to prevent damage.

And in the interest thermodynamic interesting...

Any heat energy converted to electrical energy reduces the heat from the stove.

The 45 watt generator will reduce the geat from the stove by about 120 BTU/hr (?).

Not a lot but it is real.

Ben
 
Yep, nothing is completely free.
The heat you use up doing something with cannot be used to heat. you will get no less than 10% loss in any device you use.
The internal combustion engine has almost 70% loss thermally. Only 30% of the heat generated can be used for motive power.
Your thermal conductor is likely less than 30% (probably closer to 15%) efficient so it will remove (waste) at least twice as much power as it produces.
 
See how much of that stove top in the video is open and he has a 45W generator on there? Well imagine if you had designed a system for the purpose of making power and heat and used all that surface area. I see the potential for a good bit of power production without the loss of any valuable heat. I can see the possibility of making 500+ watts when your heating your home with a purpose built system! Now wouldn't that be cool? Oh I can not wait to get my hands on some parts to make a prototype!
I come quick searching and guess 500W would run about $1000 for the cell and would require about 250 degrees F between the hot and cold side. 250 degrees for the stove may be easy but keeping the cold side at 0 degrees would be a challenge. A good heat pipe ???

Any mechanical engineers out there? This is a classic heat on a beam problem. What cross section of a copper beam would be required to keep the cold side at 0 degrees?

https://www.chegg.com/homework-help...eam-heated-center-beam-heated-centr-q13225013
Ben
 
That control box accessory should be built in to prevent damage.

And in the interest thermodynamic interesting...

Any heat energy converted to electrical energy reduces the heat from the stove.

The 45 watt generator will reduce the geat from the stove by about 120 BTU/hr (?).

Not a lot but it is real.

Ben
Okay say you're making 450 watts instead of 45 watts. Most woodstoves I am use to make 20,000BTUs an hour MINIMUM is 1200 BTU's really going to matter? Plus in my minds design the heat they "use" is what's taken away in the cooling process. Since the heat taken out in cooling will still be going in the water or atmosphere or in to the electrical power itself I would still call that a win.
 
In cold country it may work well if the hot side is circulated to an outside heatsink.
An idea I plan to work on.
Are you saying you are going to try this out also? If so PLEASE let us all know how it works out for you. I am very limited on funds so it'll take me awhile to get something going other than playing with a couple to see with my own eyes whether it works or not.
 
I have 80 junctions sitting in the garage waiting for me to get back to the project. I was going to put them around the exhaust pipe on my oil fired boiler or wood stove. Putting it on the first section above the roof would provide plenty of heat and, on the wood stove, there would be plenty of cold air on the outside as it would only run in the deep winter.
 
I have 80 junctions sitting in the garage waiting for me to get back to the project. I was going to put them around the exhaust pipe on my oil fired boiler or wood stove. Putting it on the first section above the roof would provide plenty of heat and, on the wood stove, there would be plenty of cold air on the outside as it would only run in the deep winter.
What is a junction in this case?
 
I have 80 junctions sitting in the garage waiting for me to get back to the project. I was going to put them around the exhaust pipe on my oil fired boiler or wood stove. Putting it on the first section above the roof would provide plenty of heat and, on the wood stove, there would be plenty of cold air on the outside as it would only run in the deep winter.

Nice!

Between in interior and external wall of the chimney would be good. Good thermally conductive adhesive to inside and outside.

Put all of the cells in parallel.

Keep us updated please.

Ben
 
here comes my de rail, I would be far more inclined to use thermo syphon to circulate the water, if you have enough height available.
 
I know no one asked me but here is my 2 cents worth. Using a flat sided stove polish a very flat surface on one side of the stove to allow for good contact with the TEG, then take one of those open topped flat plate water heaters
1671192299511.png

and set a copper heat-exchanger to run your cold water through with using your pump.
1671192474385.png

Strap the flat plate water heater tank to make uniform contact with the TEG cold side. fill the tank with drinking water. So now you get multiple uses out of your system. Warm water and power...

I personally would wire the TEG modules in such a way as to provide about 90 volts and then use a cheap solar panel charge controller to interface with my batteries. Now you get power in a form that you can easily store and use.

But hey that's just my 2 cents worth.......
 
TEG's can't be right on the heat source they have a max temp of 150-160 for most of them. There are some that can go hotter but none I've seen can go directly on the stove.
 
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https://www.tegmart.com/thermoelectric-modules/18w-teg-module
These are rated for 626°F/330°C and intermittently up to 400 °C (752 °F)

A flat steel plate attached to the side of a cast iron stove could provide some cooling as you will loose heat/temperature with each layer you pass through. The heat flux is what you need to generate power, so you want your hot side near the maximum rated temperature and you want the cold side as cool as possible, you also don't want to heat or cool the TEG modules too fast. They are made of very brittle materials and rapid heating and cooling can cause them to fracture due to rapid thermal expansion. They really like to operate in a steady state environment.... You also want to be careful of your module to module connections as most lead solders melt around 400°F and will not hold up well in close proximity to the high temperatures.

The high end SiGe modules have been around since the 70s and have been used by NASA for decades. They can handle a much higher hot side temperatures (~1800F):

According to Wikipedia:

Application history[edit]​


RTG Space Exploration Timeline
SiGe has been used as a material in RTGs since 1976. Each mission that has used RTG technology involves exploration of far-reaching regions of the solar system. The most recent mission, New Horizons (2005), was originally set for a 3-year exploration, but was extended to 17 years.

Multi-hundred-watt (MHW) applications[edit]​

Voyager 1 and Voyager 2 spacecraft launched in August and September 1977 required multi-hundred-watt (MHW) RTG containing plutonium oxide fuel spheres for an operational life appropriate for exploration of Jupiter, Saturn, Uranus, and Neptune.[10] Conversion of the decay heat of the plutonium to electrical power was accomplished through 312 silicon-germanium (SiGe) thermoelectric couples. A hot junction temperature of 1273 K (1832 °F) with a cold junction temperature of 573 K (572 °F) compose the temperature gradient in the thermoelectric couple in the RTG.[10] This mechanism provided the total electrical power to operate the spacecraft's instruments, communications and other power demands. The RTG on Voyager will produce adequate electrical power for spacecraft operation until about the year 2020.[10] Similar MHW-RTG models are also used on the two U.S. Air Force communications Lincoln Experimental Satellites 8 and 9 (LES-8/9).[11]
 
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Watched a video yesterday with an older gentlemen who put four TEC's ending in 706 together and made 27 watts 1.7 amps from them at 16 volts. That's nothing to sneeze at. I ordered two of the TEC's ending in 706 to try before seeing the video also have two of the TEG's on order to try. I need to see real results with my own eyes before I spend a pile of money ordering a lot of maybe useless junk. I don't mind spending $20 to learn a lesson spending $500 is different...
 
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I'm interested to see what you all come up with! I've had my eye on a rocket stove with a USB charger as a good backup for my solar generator, but they sure are pricey! A DIY solution sure would be easier on the pocketbook. I've also wondered if a bigger version could be used with a campfire in a bug-out situation. Would probably be easier to transport than solar panels!
 
What is a junction in this case?
Peltier junction, the squares with 2 wires pictured above. Hook them up to electricity and you get cold on one side and heat on the other. Put heat on one side and cold on the other and you get electricity.
 
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Peltier junction, the squares with 2 wires pictured above. Hook them up to electricity and you get cold on one side and heat on the other. put heat on one side and cold on the other and you get electricity.
Okay I just wanted to be sure. Thanks!
 
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