An idea as I sit by the fire

Ginger83 · 04-01-2022 1:21pm #1

We have a wood burning stove and use it most days, sort of a tradition and we generally love the fire.

Recently I bought a fan that sits on top of the stove and it spins when it gets warm.

I was just thinking of all the programmes I watch about people living in rural areas of the world relying on fires for heat.

Could the fan be used to charge a battery for power?

Big Lar · 04-01-2022 1:26pm

Probably not enough power generated, you could take out the fan and put an LED on it instead of the sitting room light 🙂

bullit_dodger · 04-01-2022 1:29pm

Technically....yes, but in reality the energy being transferred by the "air up currents" is "meager" at best. Probably of the order of single watts. To put that into context if your fan generated 1 watt, you'd need 2000 fires to boil a kettle!

However trapping the heat directly that's wasted going up the chimney and heating water is a very good source of free energy. We don't seem to do this much anymore as we've transitioned away from open fireplaces in homes, but the traditional "back boiler" of a fireplace in the 60's / 70's was pretty good way in heating the hot water.

Ginger83 · 04-01-2022 1:32pm

https://www.boards.ie/discussion/comment/118415428#Comment_118415428

😄

Ginger83 · 04-01-2022 1:37pm

https://www.boards.ie/discussion/comment/118415444#Comment_118415444

Ah I see it would be pointless so.

Our stove has a boiler plumbed to a 300 litre triple coil tank which heats water and rads.

mickdw · 04-01-2022 1:54pm

https://www.boards.ie/discussion/comment/118415444#Comment_118415444

Strangely we found the back boiler to be a disaster.

The fire became useless to the room it was in - possibly badly setup but it gave out no heat compared to traditional fire back now in place again.

magicbastarder · 04-01-2022 1:59pm

https://www.boards.ie/discussion/comment/118415444#Comment_118415444

those stove fans are not fed by up currents, but by thermoelectric effects which create currents between two differing materials at different temperatures, which is then used to drive the fan. the point would remain though that they generate little power.

MuttonDagger · 04-01-2022 2:05pm

https://www.boards.ie/discussion/comment/118415578#Comment_118415578

Agreed ,

Great in theory but not in practice.

reklamos · 04-01-2022 2:10pm

https://www.boards.ie/discussion/comment/118415606#Comment_118415606

This. The device is utilizing Peltier effect. You can buy peltier element separately. I had device made and used CPU heat sink and fan. Placed it on top of yankee candle jar and it worked. The thing is you need a fan to cool the cooler as otherwise the difference is not big enough. So although it does generate small amounts of power you will use that power for fan. Unless you can achieve efficient passive cooling.

bullit_dodger · 04-01-2022 2:48pm

https://www.boards.ie/discussion/comment/118415638#Comment_118415638

You might be thinking of a different thing. House I grew up in in the 70's had (essentially) a gallon or so reservoir of water in behind the normal fireplace. Set into the brickwork. For all intents and purposes it was a normal fireplace from look/feel. This was plumbed to the hot water tank and heated the water by convection, no pump. It must have had some form of expansion safety value, but thermodynamics wasn't something I thought much about when I was 6 or 7 years old - LOL.

It was slow as in it took 2-3 hrs to heat the hot water tank in the hotpress, but it worked pretty well. No difference in heat out of the fireplace, though back then burning coal was the norm and of course that has a much higher temp than what we'd use today.

To go back to the OP here, lot of heat/energy going out chimneys.......wasted. Trick is capturing it.

graememk · 04-01-2022 3:01pm

https://www.boards.ie/discussion/comment/118415578#Comment_118415578

Running a fire with a back boiler is a totally different scenario than one without.

Generally you'd need a bigger fireplace to allow for a bigger fire and you need to be constantly feeding it.

Granted the heat isn't wasted, it's usually sent around the house/to the hot water. The heat that the boiler captures is constantly being pulled away. I grew up with them and still use a solid fuel stove.

Whereas you light a small fire in a "normal" fireplace, whatever doesn't go up the chimney goes into the room. & If you ran that fire like one for a back boiler, you'd be put out of it.

To get back on track, a Stirling engine is probably possible but not worth the hassle

Ginger83 · 04-01-2022 3:55pm

https://www.boards.ie/discussion/comment/118415991#Comment_118415991

Would a Stirling engine device charge a battery?

graememk · 04-01-2022 4:34pm

https://www.boards.ie/discussion/comment/118416410#Comment_118416410

Short answer Not really

But there is stove fans based on the principle https://www.stirlingengine.co.uk/d.asp?product=VULCANSTOVEFAN

Ginger83 · 05-01-2022 12:45pm

https://www.boards.ie/discussion/comment/118416676#Comment_118416676

The Stirling engine was a great invention but it's such a pity nobody has been able to use any real power from it for domestic use.

harderthanf · 05-01-2022 4:23pm

As someone mentioned, they use peltier modules - they can be used to create fridge/cool conditions too. I have had a few over the years and one got very noisy so I took it apart and tested it on the stove. With the heat from my stove I could certainly have charged a phone. I was seeing slightly over 5V and up to 1amp of current. IIRC I put it on a board with a tp4056 too and it managed to charge a 18650 fine - over a good few hours. The biggest problem was the heat on the cables!!

Herself wasn't too happy with the look of it so I didn't get past 1 or 2 nights testing

Ginger83 · 05-01-2022 7:52pm

https://www.boards.ie/discussion/comment/118421956#Comment_118421956

Yeah I had a 1.2m satellite dish put up recently but herself is not very impressed 😁

harderthanf · 05-01-2022 10:31pm

https://www.boards.ie/discussion/comment/118422930#Comment_118422930

Hah - I had one a few years back too - motorised for the full arc. Lasted a few months too before there was uproar! Ah well....

Ginger83 · 05-01-2022 11:35pm

https://www.boards.ie/discussion/comment/118423813#Comment_118423813

😂

An idea as I sit by the fire

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