Does a spring mechanism exist for a ventilator?

[stovemakerParticipant @stovemaker]

Hello, i realise this is an unusual question but in trying to invent a spring powered stove. Not for Cooking, just warming. For that, i will need some spring mechanism that takes as long as possible to wind down ( hoping for 20 minutes or so) and that would be able to drive ventilator blades for that time . Does anybody know if this exists , or even can be done?

(The warming part is taken care of by another mechanism..)

[Les Jones 1Participant @lesjones1]

Is this a coil spring ? (Compession or extension.) Or is it a flat spring like the hair spring on a clock.
If it is anormal coil sprin you could add a cylinder with a piston in it linked to the spring You would need a valve to adjust the amount of leakage between the ends of the cylinder to control  the leakage between the ends of the cylinder.

You might alro want to add a non return valve to that the piston could be moved quickly in one direction. The cylinder could be filled with oil of a suitable viscosity.

Les.

[noel shelleyParticipant @noelshelley55608]

Please clarify what you are trying to achieve ? Is it a circulating fan, then a stirling engine does this. Your spring will need to store the energy to power the fan. How do you load the spring, tension or compression. Noel.

[JasonBModerator @jasonb]

Clockwork fan is what you want

This is a 3D printed one but easy to make a metal version from the downloaded files

[BazyleParticipant @bazyle]

This is like a kitchen timer, before they all went electronic, ie a simple clockwork mechanism. You just need a bigger one. Big clockwork is not very common now but the mechanism from an old gramaphone would be about the biggest you could get.  Another example going back little further is the weight driven roasting spit.
Other possibilities are a piston damper with a valve to adjust ow fast the air/liquid escapes. These normally are rather shorter times.

[John HaineParticipant @johnhaine32865]

Read up on Trevor Bayliss’ wind-up radiator.  Uses a “tensator” spring IIRC.  Or, if you have some waste heat, use a peltier element as in the cheap stove fans from Aldi etc – provides the motor and fan as well.  Depending on the temperature available some modification may be needed.

[noel shelleyParticipant @noelshelley55608]

You need the punkka walla from it ain’t half hot ?  The Swiss job is beautiful though rather noisy, The near silent tangential fan unit from an old fan heater would be easier and the motor consumes  very little power. Or build a double skin round your heat source with a blower unit to circulate the heat, like the Jetmaster fires of the 80s. Noel.

[SillyOldDufferModerator @sillyoldduffer]

Excellent project!

I agree with the others though – to get a good answer can the requirement be explained in more detail please?   My first guess was a circulating fan, they ensure even heating by stirring the hot air inside an oven.  The guess feels wrong because ‘ventilator’ has been mentioned, suggesting the purpose is to remove exhaust gases or maybe cooking smells.  Outside through a vent, or into a filter?   All these imply a fast running fan like Jason’s example.

Need to know how much work (scientific definition) the fan has to do, which derives from the required airflow measured in cubic metres per minute or similar.  A guesstimate will do, but there’s a big difference between the power needed  to ventilate a canteen kitchen and the power needed to ventilate a camping stove!   If the airflow is known I can dig out the formula converting it into a power requirement in Watts.    Then, knowing how long the fan has to run for gives watt-hours, which determines how big the spring needs to be.

Be warned though that springs aren’t a good source of power – they can’t store much energy.   Good for clocks and toys, and for storing and returning energy in short bursts like a car suspension, but not when power has to be sustained for yonks.  You may find a massive spring is needed!  This is why big mechanical clocks, grandmother size and up, are usually powered by weights, not springs.   Not as neat as a spring though!   Also why most ventilating fans are driven by electric motors.  I don’t know how long Jason’s hefty Swiss fan would run, I guess less than 10 minutes, probably much less.  Does that matter?

If a chimney is available a fan may not be necessary.  A chimney is a form of heat engine, and once hot likely to outperform a small fan in terms of volume of air shifted.   May not be practical, and size matters; big chimneys work much better than small ones.

Even the form of fan is open at the moment.   Propeller blades provide velocity, whilst centrifugal fans move volume.  May not matter.

Is heat going to be a problem?  Many small fans have light plastic blades that will deform.   Might be possible to replace them with metal blades, but these take more energy to spin, making a bigger motor necessary.   Fans are fussy about speed, become inefficient as RPM falls, and may fail to ventilate adequately.  Spring driven fans being on the weak side need all the help they can get.

Have a cold hard look at spring driven fans, because they may not be suitable for this project.  In comparison,  electric motors provide a lot more leeway.  If electricity isn’t available, then a complicated Stirling Engine is worth considering.

If tackling the problem with numbers and nailing down the requirement as described above is unattractive, the alternative is to experiment.   Though experimenting is good fun, and is often essential, it can get expensive in time and money.   Painful to cough up to build or buy the biggest spring driven fan in the world, only to find it has to run for 40 minutes, and can only manage 4…

Dave

 

[JasonBModerator @jasonb]

The old one in the video runs for 30mins, more than the 20mins the OP wanted. Seems a wind up spring is more than adequate.

No doubt gearing it down to a slower speed to just move the hot air will allow it to run for even longer

[noel shelleyParticipant @noelshelley55608]

Taking the ops nom de plume as a clue it is not a ventilator that is needed but a circulating fan, is the need for a spring driven thing because he is in an ” off grid ” location. More info please. Noel.

[JasonBModerator @jasonb]

He did start two threads, from the other

Hello, im from the Netherlands and im trying to invent a wind-up stove. Only for warming a smallish room, not cooking.

What i am looking for is a wind-up mechanism , therefore im here!

[Michael GilliganParticipant @michaelgilligan61133]

If we are actually considering a circulating fan for a heating stove in a small room, then the obvious choice would seem to be something like this:

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MichaelG.

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Edit: __ I bought one to play-with [sometime]
A fancy extrusion supports a small electric motor that powers the bladed fan

Electricity is provided by a Peltier element so, when the stove is up to temperature it is self-sustaining.

A more substantial version should be a nice project.

[stovemakerParticipant @stovemaker]

Hi Dave, Noel and others,

Yes , i realize more info is necessary. My idea is to create a vertically positioned central  circular plate, equipped with alternating magnets along its edge. I would rotate 2 circular aluminium fans, one on  on either side of it, so 3 circles parallel (think of the wheels of a car with the central plate as the motor driving the axis between them)

Bij induction, this should heat up the fans. Of course, these would have to be a special shape – a sufficiently large area right next to the magnets with enough skin depth (The surface layer of the aluminium where eddy currents occur that heat up the metal), and further away from the magnets a shape that would catch the air, and provide maximum heat transmission before releasing it.

This way, i would only have to power the 2 rotating fans. A thing that possible could be done with only a clockwork spring, or maybe something  Weight powered.

My greatest concern at the moment is the speed. You’d need at least 500 rpm to get any decent results i think. I wonder if it is possible.

As for the airflow, it really only has to be a ventilator, ciculatng air, while heating it in the process.

[JasonB]

On JasonB Said:

He did start two threads, from the other

Hello, im from the Netherlands and im trying to invent a wind-up stove. Only for warming a smallish room, not cooking.

What i am looking for is a wind-up mechanism , therefore im here!

Missed that, and it simplifies the requirement considerably!  In that case a big wind-up fan is a reasonable answer.  No need to worry about heat melting anything and when the spring runs down, just wind it up again.

I wonder what the source of heat is?   Anything with a flame is inefficient unless it gets air from outside, because combustion pulls cold air into the room as well as warming it. A room with a roaring open fire in a hearth is toasty hot, but a lot of fuel is wasted, much heat escapes up the chimney, and the rest of the house is chilled because cold air is pulled through it from outside!   Central heating is much better.

When I was little, the whole family had chilblains every winter.  Haven’t seen frost on the inside of a window since, ah the good old days…

Dave

[stovemakerParticipant @stovemaker]

Wind-up radiator?? Do you mean radio? And i’m afraid the amount of energy a radio needs insn’t all that much…

[duncan webster 1Participant @duncanwebster1]

The overall description includes an eddy current brake (being driven by something unspecified) which creates heat. This must be capable of delivering a sensible amount of power, so why not just gear up the eddy brake shaft to drive the fans?

[John HinkleyParticipant @johnhinkley26699]

+1 for what John Haine and Michael Gilligan suggested.  Any number of them available at little cost if you search for “log burner accessories”.  No batteries, mains or clockwork involved.  Once it’s up to speed, it is apparently self-sustaining, until the heat source is removed.  I have no experience of using one; our log burner in France put out about eleven kW on full chat. Real toasty!

John

 

[Michael Gilligan]

On Michael Gilligan Said:

If we are actually considering a circulating fan for a heating stove in a small room, then the obvious choice would seem to be something like this:

.

.

MichaelG.

.

Edit: __ I bought one to play-with [sometime]
A fancy extrusion supports a small electric motor that powers the bladed fan

Electricity is provided by a Peltier element so, when the stove is up to temperature it is self-sustaining.

A more substantial version should be a nice project.

Thanks for finding the example, Michael.

My son and DIL have one of these atop the wood stove in their living room.

They’ve had it a few years now.

It starts automatically as the stove heats up, works well at distributing the heat and AFAIK has given them no trouble.

[old martParticipant @oldmart]

The wind up mechanism for an old gramaphone springs to mind. They go down to 16rpm and would last over half an hour easily. When I was a kid, I used to take them apart and reassemble them, the springs were tricky to uncoil and replace in their drum

[Robert Atkinson 2Participant @robertatkinson2]

While the OP may be holding back for commercial / IP reasons, on the information provided this looks like a “free energy” device. Using eddy currents from permanent magnets to generate heat is pretty inefficent. The energy has to come from whatever is driving the disks. If this is a separate power source then it seems strange to use a spring for the ventillator. If the spring is the sole source of energy it would have to be pretty big to generate useful heat.
Energy in a perfect spring is 1/2 the spring constant times the extension squared. A 100N/m spring stretched 1m stores 50J. That is 50 Watts for 1 second or 0.000216 kWh Not a lot.

If you want a “wind-up” heater a generator charging a super capacitor (or battery depending on time between winding and heat production) that is then discharged into a simple resistive element would be a simpler approach. The fan can be electric.

Robert.

[stovemakerParticipant @stovemaker]

Well, im not trying to make money with this, its just an idea for poor people in cold places like Moldavië or Rumenia who may not have enough money for both food and firewood. So im looking for a warming device that can be powered with only a spring or a clock weight. But Robert is right, you dont get more out of it than goes in .. i dont believe in free energy. An alternative might be a “spinning wheel” construction, where you have to keep pushing the pedal.

[noel shelleyParticipant @noelshelley55608]

Another avenue that might be worth looking at would be to draft proof a house or room to keep in what little heat they do have and construct a simple wood or waste burner. Good luck. Noel.

[stovemaker]

On stovemaker Said:

Well, im not trying to make money with this, its just an idea for poor people in cold places like Moldavië or Rumenia who may not have enough money for both food and firewood. So im looking for a warming device that can be powered with only a spring or a clock weight. […]

In that case, I would suggest weight driven

The weight could be a rock, or ‘most anything … and the winding by Huygens’ endless device.

MichaelG.

[John HaineParticipant @johnhaine32865]

Please just do some basic sums.  10kg weight exerts about 200 Newtons.  Lift it 2m, you’ve stored 400 joules.  If it drops in 100 seconds that’s 4 watts.  Frankly you’d get warmer just weight lifting.

[Michael GilliganParticipant @michaelgilligan61133]

Starting from John’s benchmark numbers …

• Increase the weight
• Reduce the power requirement of the fan
• Adjust the gearing accordingly

There must be an optimum in there somewhere

I was thinking in terms of one Huygens-rewind every hour or so

[ the demonstrably effective Peltier-powered devices typically use quite a small  fan ]

MichaelG.

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