stove fan

Topic: stove fan (Read 1415 times) previous topic - next topic

stove fan

November 28, 2018, 07:17:42 PM

i bought one of those "heat powered" stove fans you simply set atop your wood stove,, the heat off the stove causes an isolated electronics part to generate power because of it. i know ,,, sounds like magic stuff in a bottle but read on,,, these things are real and im sure someone here will be getting a few for christmas.

inside of one use , i burned it up so i went on an exploration mission to determine what i had done wrong.

i had to learn about a product i had no knowledge of its existence.

the gizmo that converts heat into electricity is something call a Peltier effect. this tech is not that old and still kinda in its trial and error stages of engineering applications although you find them randomly on some high end cooling and de-humidification systems.

there are two types...
TEC- thermal electric cooler

TEG- thermal electric generator

the TEC has a lower withstand point in deg F than a TEG.

they both actually do a somewhat similar job but are designed a smidge differently,, yet each has its own application.
the tec has a lower output voltage as well so in my mind started to arrive at basic conclusions.

Come to find out the stove fan came equipped from the maker "Voda" with a TEC.

I took the bugger apart to understand what kind of electric motor drives the fan blade and discovered its a brush motor and it seemed to be ok with a 9v battery source, i did not put 12v on it figuring i was pressing my luck being i knew this motor design was never expecting to see any voltage higher than 5vdc when the TEC or TEG was on max.

Back pedal here a tad..
the TEC is 1/8'' thick by 1.5'' x 1.5'' device with a red and black wire hanging off it.

I researched out where i could find TEG's and there are mil-spec opitions, industrial options, then there are hobby options so i shot out an order to china for some cheapy renditions to tinker with... got a dozen of them on ebay for under 2$ ea.

I tossed out my defective one then installed 2 TEG in series thinking i would double my voltage potential which the results yielded a great operating fan.

these are very interesting units because all you have to do is have one side get warm while the other side stays at a different or ideally "lower temp by way of a mounted heat sync... if you do this the two wires will put out voltage and current proportional with the temperature difference the unit is experiencing. ~~ cool stuff eh???

here is a vid i did real quick......... i mispoke in the vid,, i think the TEG can go well over 200degF

https://www.dropbox.com/s/usc7p8ec801pzcp/VID_20181126_203747.mp4?dl=0

stove fan

Reply #1 – November 28, 2018, 10:39:28 PM

very cool devices. I first learned about them a while ago. not very powerful, but extremely simple and versatile.

I first discovered them in this super nerdy show I watched, https://www.youtube.com/watch?v=niMGlHtOhyA&t=10s
really neat seeing what people can do with them.

stove fan

Reply #2 – November 29, 2018, 10:34:16 AM

now... that guy in the vid is injecting power into the unit to trigger the TEC he is using.

just so other readers are clear....

TEC's and TEG's will produce voltage and current if just heat is applied to one side and the other is kept cooler.
the greater the differential or temp rise,, the greater the voltage (up to about 5vdc) and current is.

stove fan

Reply #3 – November 29, 2018, 10:48:07 AM

can you imagine some of the TEC's ganged along a throttle body air intake,,, meaning if you intentionally lengthen the runner out the fender, down, across the nose and back up on the other fender,, a bunch of these coolers cooling down the intake are.

stove fan

Reply #4 – November 30, 2018, 10:21:07 AM

"A Peltier cooler can also be used as a thermoelectric generator. When operated as a cooler, a voltage is applied across the device, and as a result, a difference in temperature will build up between the two sides. 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."

yes, just for clarity, they can be used both ways, it looks like they may change the composition slightly to make its intended purpose more efficient. But very interesting and useful devices that can serve many roles.

stove fan

Reply #5 – November 30, 2018, 12:04:00 PM

Quote from: jcassity;468151

can you imagine some of the TEC's ganged along a throttle body air intake,,, meaning if you intentionally lengthen the runner out the fender, down, across the nose and back up on the other fender,, a bunch of these coolers cooling down the intake are.

Peltier coolers are nice when you want quiet operation or are in antagonistic environments (corrosion, vibration), but they really suck at efficiency. Coefficient of Performance (COP) is a measure of heat generated/moved versus power consumed. A COP of 1 means you made 1 Watt of cooling and used 1 watt of energy. COP of 2 means you made 2 watts of cooling and used 1 watt of energy. The A/C on our cars runs between 1.5-3.0 COP. A heat pump in our homes has a COP of ~3.5-4.5. A peltier cooler runs somewhere around 0.5 COP.

It takes roughly 4.7kW to cool 300 cfm of air down 50 degrees.
Btu/hr= cfm*delta t*1.08 Watts = Btu/hr * .293

For a COP of 0.5, you need 9.5kW of input energy to get 4.7kW of cooling effect. Do they make 1000A alternators? :hick:

I think some SVT had a secondary refrigerant loop that had an evaporator in the intake that could cool the incoming air. Using the A/C compressor is a much better application as they can absorb 4+ kW of power and have a COP >1.

stove fan

Reply #6 – December 01, 2018, 05:59:16 PM

Quote from: JeremyB;468166

I think some SVT had a secondary refrigerant loop that had an evaporator in the intake that could cool the incoming air. Using the A/C compressor is a much better application as they can absorb 4+ kW of power and have a COP >1.

Yeah, was on some years of the Gen 2 Lightning, not sure if it made it's way onto the Cobra Mustangs..