DIY Thermoelectric Power

[cwhaley]

I have a wood burner which I run with free timber (well, it’s a lot of labour but it doesn’t cost anything).

I managed to salvage two CPU fans from work (see link showing similar item) and I’m planning on putting them behind the stove to push stagnant heat forwards. I have a stove-top fan and it’s okay, but looking to move more of the heat around the room.

Does anybody know what is needed - if it’s possible - to generate 12v at just under 3w through something thermoelectric? Mounted on the top of the stove is there anything that could convert the heat to this amount of electrical energy?

https://www.amazon.co.uk/dp/B0BZH85FRX/ref=sspa_mw_detail_0?ie=UTF8&psc=1&sp_csd=d2lkZ2V0TmFtZT1zcF9waG9uZV9kZXRhaWwp13NParams

 

[ericmark]

The sterling engine is what is normally used, but as to making a DIY model not sure how.

 

[cwhaley]

The sterling engine is what is normally used, but as to making a DIY model not sure how.

Yes the principle is the same as my current stove-mounted fan. I wanted to have a bank of fans mounted behind the stove, slightly off the wall so that air could be drawn up behind them (in the fireplace opening) and thrown forward into the room.

I've seen the heat patches, but not idea how to use them (they don't look very 'pretty' nor wire them up). Will keep looking for a solution.

 

[AkiraDIY]

peltier modules are designed to generate electricity from heat although I'm not sure if they can handle the high temps of a wood stove. They're cheap-ish and significantly easier than constructing a stirling engine

 

[cwhaley]

peltier modules are designed to generate electricity from heat although I'm not sure if they can handle the high temps of a wood stove. They're cheap-ish and significantly easier than constructing a stirling engine

Thanks, yes the fan I have uses one of these although it is of course not mounted directly onto the stove. It sits between the base of the fan and the mounting for the motor, so it raised about 3" off the surface. I'll see if there are units for these.

 

[AkiraDIY]

The modules need heat on one side and cooling on the other, you'll need to source a couple of heatsinks as well. The greater the difference, the more wattage is generated. Definitely get ones that will easily power a bank of low wattage PC fans but not sure what the general operating temps would be a couple inches off the stove. Need to get a temperature probe out and check next time I get the fire on.

Let us know how you get on, I would be interested to know if you manage to get it working. My stove was installed too close to the back wall so some extra air circulation would be beneficial for me too.

 

[ericmark]

remount boiler on the stove, it would make a great talking point!

To be frank I used mains power and sensors to keep the flue at correct temperature. The problem is too cool and particular emissions and flue tars up, too hot and wasting energy, we did a lash up in a friends house to try to control it, but it was a failure.

The rocket

was claimed to work well, but not seen one in use, these are claimed to burn efficiently, however one would need some UPS for those fans and pump, should they fail and we would have a big bang. I was involved with the set up on my sons narrow boat, he had a rayburn stove with side boiler, but in a narrow boat no where for a header tank, so he used two 12 volt DC pumps, designed so if one failed the other took over, however not sure even with that is would comply with the RCD? (Recreation Craft Directive)

 

[AkiraDIY]

A stirling engine by itself is kinda expensive and difficult to DIY into a fan. Better to just buy one if you want the talking point and for it to be effective. Looks cool but crazy expensive.


Side note, found this instructable so it's possible with a cheap peltier module. https://www.instructables.com/DIY-Stove-Fan-for-under-50/

 

[cwhaley]

Thanks all for the tips.

The fans I have are just CPU fans mounted on the wall behind and to the side of the stove. They just need a 12v input so I'm looking at a way of generating that power through something on the stove top. I don't want another fan on the top as I think the heat is better pushed from behind the stove where it accumulates in the opening.

 

[Murdochcat]

Are you sure the fans you have will withstand the heat coming off the wood burner?

 

[RandomGrinch]

For the peltier to operate, it requires a hot side and a cool side.
Hence the elaborate design of stove fans - they have a heat sink on the cool side behind the fan; the fan once operating, takes cooler air through the heat sink, removing heat, cooling the cool side of the peltier.
Without this forced cooling, there won't be a great enough heat differential for the peltier to operate.

Here's an example for the specifications of a typical 40x40mm peltier...

With a rated voltage of 3V, this may not be a suitable power source for PC case fans.

Basically, peltier based stove fans are the form they are, because that is the optimum design to get them to operate.

A setup to operate a bank of PC fans will require a slightly more unorthodox approach!

 

[cwhaley]

Are you sure the fans you have will withstand the heat coming off the wood burner?

Nope, no idea! They're free so it's worth a shot, plus there's a good gap of about 8" behind the stove so they're not going to be too close.

 

[bernardgreen]

There are many heat powered fans designed specifically for use with stoves

One of many suppliers is

Stove Fans

A UK Stove Fans woodburning stove top fan can help reduce your fuel usage by 33%. A stove fan on your woodburner helps evenly spread heat from your fireplace into the room providing heating benefits. As you feel warmer you will burn less fuel to obtain that desired warmth. Low noise, zero...

ukstovefans.com

 

[bernardgreen]

Being pedantic

Peltier effect uses electrical current to cool items ( solid state heat pump )

Seebeck effect generates electrical current from heat.

 

[cwhaley]

There are many heat powered fans designed specifically for use with stoves

One of many suppliers is

Stove Fans

A UK Stove Fans woodburning stove top fan can help reduce your fuel usage by 33%. A stove fan on your woodburner helps evenly spread heat from your fireplace into the room providing heating benefits. As you feel warmer you will burn less fuel to obtain that desired warmth. Low noise, zero...

ukstovefans.com

Yes I do have a stove-top mounted fan.

My plan was to mount two fans on the fireplace opening wall (behind the stove, plenty of room) and have them running to push the air from around the sides of the stove.

There is a wire ran at the back of the fireplace which powers some alcove shelving lighting, and I could easily power the fans from a junction at that wire, but it's another thing to switch off and it seems daft not trying to harness the heat energy coming from the stove to power them!