Cheap Stove top fans

[ivan]

Bought a few of these, and with the limited testing that I've done, they seem pretty good. I paid £5 each...
Bargainfox prices change quite a lot. They currently have two models for sale at £8.60 and £3.60. All sorts of odd stuff for sale on their site.

https://bargainfox.com/en/products/B0DBVF7BG9

https://bargainfox.com/en/products/B0DDKGJKQG

[MikeNovack]

Odd that they self describe these as "non-electric". By appearance (and cost) look to me to e Peltier effect powered. Thermo-electric is still electric. I suppose by non-electric they meant no external electric power.

The issue with using Peltier in this application, is critical that the cold side manages to dissipate heat fast enough to stay cold and the device remaining running.That's because otherwise the Peltier device could cook. A wood stove top is way above the maximum operating temperature of a Peltier device. So ..... the question is, cheap, but do they hold up?

The Stirling powered devices cam easily withstand the temperatures. But going to be far more costly, an order of magnitude more, and may not be self starting. Self starting Stirling is HARD. So fan might need a finger flip.

[ivan]

Most TEGs - thermo-electric generators (sometimes known as peltiers....but peltiers are intended for using the opposite way - to generate heat (and cold) from electric) have maximum junction temperatures of 120Cish - ie the temperature at which the solder becomes unstable and over time starts to move. So if you look at the fans - they normally have some kind of pedestal, with an I-beam type profile, which slows down rate the heat flows to the TEG sufficiently to keep below the maximum temperature at the solder junctions. Usually, the stove fans have a bimetal strip under the base, which will force the fan to tilt slightly at high temperatures, to act as a safety device in the event of high temperatures. Not foolproof - eg if you make the top of your stove glow orange - but generally will keep things working. I've been using various stove-top fans including some home-made ones over 20years or so, and only ever knackered one (home-made one).

I've also played with a couple of stirling engine stovetop fans. They are much more expensive, hard to start, and very noisy, so not my first choice for this application. I presume they're probably rather more resistant to overheating, but due to the noise, I've never run them for very long. I've got a solar stirling engine too - a couple of watts, and again very noisy. Not sure how long it would last if it was run continuously.

[MikeNovack]

I've also played with a couple of stirling engine stovetop fans. They are much more expensive, hard to start, and very noisy, so not my first choice for this application. I presume they're probably rather more resistant to overheating, but due to the noise, I've never run them for very long. I've got a solar stirling engine too - a couple of watts, and again very noisy. Not sure how long it would last if it was run continuously.

a) LOL -- yes more heat resistant. The practical limitation on Stirlings is that the hot end can't be so hot the Nitrogen in the air gets involved (so no longer "clean burning"). The hard to start (not self starting) is typical of the Stirling. It is HARD to design a self starting Stirling. Usually must be of the "free piston" sort as VERY LOW friction is a must if to be self starting.

b) With solar as the heat source, not going to be a huge temperature difference unless an array of reflectors is used. The plant here in the US that was doing solar that way just shut down (end of life). Typical of a design like that, the collector is up a tower and an array of mirrors on ground mounts move to focus on that spot.

[ivan]

I made a solar thermal-powered radio years ago - I took 4 or 5 vacuum tubes with heatpipes. Put the heatpipes into a block of aluminium and onto that put a few TEGS with heatsinks, connecting their outputs to a low voltage (3.6v?) radio, and left it against a wall in the garden. On sunny days, the radio would burst into life. Not much point, but fairly interesting!