A vaugue question from the UK

I have a wood powered stove for my central heating, to assist circulate the warm air I have a stove top fan which is specified to start working at 50 degrees, my stove has a water jacket over and to the sides of the firebox therefore the top of the stove normally only reaches 30 degrees. The fan is powered by a peltier pad between two metal plates one heated the other not to generate the electricity to operate the fan blades.
My query is there a peltier pad that would start generating power at a lower temperature or are they all the same specification ? the pad measures 40 mm square if that is any help.

Hi @Art, welcome to our forum. Do you know by chance the specific model that was installed in this application?

These devices vary widely, one of our other Application Engineers wrote up a few articles on this topic that might interest your comparisons:

https://www.digikey.com/eewiki/display/Motley/Thermoelectric+Modules%3A+Device+Specifications

Regards,

Peltier devices used for generation require a temperature difference between the two sides of a device to perform their magic. The smaller the temp difference, the less electrical power one can get out of any given device. At a hot-side temperature of only 30(°C?) one won’t get much at all unless the cold side (room temperature in this case) is kept uncomfortably cold, which would sort of defeat the purpose of the whole arrangement…

Peltier devices are not all created equal, but even the best can’t function in the absence of the intended energy source; even the best solar panels don’t do much when the sun isn’t shining. It’s the same concept here.

Hello Robert,

Many thanks for the reply, I am enclosing a photo of my fan made by a company called Valiant, I did make an enquiry with them but they were unable to provide any help.

I will try to dismantle the fan to see if there is any specification details marked on the sensor.

I am also enclosing a photo of my dirty stove top first thing in the morning before fueling, there are fans that fix to the flue pipe but as you can see due to the space available the pipe has a double bend before exiting into the chimney.

Not knowing anything about these sensors I wondered if there were models that started generating electricity for the fan at a lower temperature,

Thanks,

Art

Hello Rick,

Many thanks for the reply, from the information you have given I now have a better understanding of how the system works in an ideal world, The flue pipe reaches the temperature that should generate enough electricity but as you can see from the enclosed photo my pipe has a double bend which seems to make fitting a fan on the flue pipe a difficult option.

Again thanks for your reply.

Art

The base of the fan assembly, besides providing clearance for the fan blades, also serves to limit heat transfer; most commercially available peltier devices will melt and fall apart at temperatures between about 140 and 240°C depending on the solder used in manufacture, so such a limitation is needed for products of this sort to not be returned as defective when somebody sticks then on a half-cm thick piece of steel with a 1500°C flame on the other side…

Since you’ve got a mechanism (water jacket) that should keep things from getting too hot for the peltier device, you might find some success if you can get rid of that bottom portion and mount the hot side of the peltier device directly to the water jacket. You’d have to be clever about accommodating blade clearance and good luck getting things apart if it’s been epoxied together (which looks likely…) but if you can’t return for refund or gift to somebody with a more suitable stove, that might be your next best option.

image

Note that a peltier device used as a generator functions much like a water wheel or windmill in concept, save for using thermal energy as its working fluid instead of water or air. It’s not a sensor so much as an energy conversion device.

I could imagine how one might be able to form a fairly thin piece of tin or aluminum in a semi-circle which could be clamped onto the flue pipe, and then bolt or weld an angled piece of metal onto that which could act as a base for your fan.

The potential problems with this would be whether or not it would be sufficiently thermally conductive to generate the temperature differential required to power the fan, and whether it would be aesthetically pleasing. Your fan is almost a piece of art, and such an adaptation would likely take away form this style. However, careful design and a good paint job would go a long way toward improving aesthetics.

Rick,
Once again thanks for the information all of which I was unaware of.
Having bought the fan 4 years ago and not seeing it working became irritating resulting in my seeking advice which thanks to you I now know that what I own is now a conversation piece with my visitors :smiley:
The room and house are heated sufficiently to be comfortable without the fan working so no problems with the room temperature.
Regards,
Art

Hello David,
Thanks for the reply and suggestion, I think as I have managed to heat the house sufficiently without the fan working I will just forget all about it and leave it on the top of the stove as a conversation piece :grinning:
Art