[Stoves] Using a differential windlass as motive power for stove

[drew]

Hi Steve, 

Thanks for the comments,   lets reframe your evaluation a bit. 

If your fan is 3w what is it's efficiency?  50% electricity to torque 
let's be generous and call it 70% and what's your charger to battery 
eff?    What's the windlass eff, I think likely greater than 90%.    
What is the average burn time of these types of stoves?   somewhere less 
than 1/2 hour, not the two hours you have used.   What if someone had to 
reset the weight once or twice or even 3 times in that 1/2 hour,  then 
really the time it needs to run is 10 minutes not your stated 2 
hours.    Looking at it that way might be more helpful.    In 
blacksmithing much larger btu outputs are readily produced using very 
little energy, the old stories about needing a boy to pump a blacksmith 
bellow, is just an old story  (I know, I have done it).   So given those 
circumstances the mass required is 1/12 or less than your predicted 
540kg more like 33 kg, and that is not even calculating your electricity 
to shaft hp conversion which likely reduces that weight by close to 1/2 
or 15kg.     Given that most people cooking on these stoves problems 
don't expect to set and forget ,but are actively there tending the food, 
I think run time of less than 5 minutes might be fine getting the weight 
down to 7.5kg something close to what your would find in a clock, 
surprise :-) .     For the less technical on the list you might consider 
applying your formula to these numbers and see what you get.
    It's not that I consider electricity to be high tech, or that high 
tech is necessarily bad, I would just say that it is not always 
appropriate.   A fan with pulse width modulation control, a battery 
(lead?), a charger (solar? thermocouple? diodes?) ect. is certainly high 
tech to most people in the third world.   A stove that local people can 
make, is one they can repair and therefore the design can propagate 
locally providing jobs and training for local budding business people, 
to paraphrase badly  "send fish, people eat once,  teach people to fish, 
and people eat forever".     You might find Schumachers book "Small is 
Beautiful"  a good read in many ways I think it would be fair to suggest 
he started this whole movement.   Once again I will say that I am sure 
there is a place for electric blowers, but would also insist that the do 
not belong in all scenarios.

All the best
Drew


Steve Taylor wrote:
> drew wrote:
>>     So a simple electric fan alternative that might be explored is a 
>> fan based on a differential windlass.    Differential windlass 
>> systems were often the motive force behind grandfather clocks (taking 
>> the high torque low rpm energy from a slowly dropping weight and 
>> turning it into a high rpm low torque) . 
> Lets say we need 3W for a blower (underrated, in my estimation), and 
> that we are going to dissipate the energy over a burn of say 2 hours, 
> we need to hold
> 3x3600 joules =10.800 joules. Lets raise a weight say 2 metres (just 
> under 7 feet), what weight do we need ?
> 10,800=MxgxHor M=10800/2/10 =540 kg, half a ton. Is that practical ? 
> Double the height (14feet), 270 kg, double it again (28 feet), 123kg.
> Is that practical ?
> Electricity in the 21st century is not high tech.
>
> Steve
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