Possibility of a Mechanical Generator

by PraAnan
Tags: generator, mechanical, possibility
 P: 42 One more bump to see if anyone can help me.
 PF Gold P: 866 Hi PraAnan, The bulb you have is pretty modest, 12V and 5watts means it uses 5/12 = approx 0.4 amperes when running, so your 4amp hr battery will run the bulb for around 10 hours. The battery is almost enough to run the bulb for 12 hrs by itself. That suggests that what you need is a trickle charger that generates about half an amp at 12 volts. Most homebrew electric motors or generators don't get that much voltage, but hopefully you could find an old bicycle generator that would fit the bill. Of course that does not meet the spec of a 2 min reset, someone would be pedaling pretty steadily, but it would work. The meaning of the 15 watt in 12 hours challenge is still not clear. Watts are a measure of power, volts x amps, so does he mean achieve a 15 watt peak sometime in a 12 hour period or maintain a 15 watt output over a 12 hr period?
 P: 42 I find it easier to tell it in joules: Either the ability to generate 18,000 joules continuously every hour. or Generate a minimum of 54,000 joules in a 12 hour period. I find myself thinking that anything mechanical won't work for this project because with a 50% efficiency I would need to generate 36kj in the 2 minute reset time which is 300 watts. For the latter option you would be able to cycle for a total of 24 minutes and you would need to generate 75 watts. This seems reasonable.
 PF Gold P: 866 A world class biker can produce 300-400 watts for a 20 minute interval, as can be seen during the climbing stages of the Tour de France and similar races. Suitably drugged, some have produced 500 watts, Floyd Landis for instance in an epic race stage which led to his exposure, because the results were just too good. So 300 watts for 2 minutes might be within reach if you are blessed with a very fit friend. The 75 watts for half an hour should be a snap for anyone reasonably fit, although 50% conversion efficiency is optimistic. Plus you have to scrounge up the needed generator. Maybe you could get an old generator from a junk car. Those are 12 volts and they come with the drive pulleys attached, which should simplify the task of making it spin. Also note that there is no reason why you could not have several people helping turn the generator, which would alleviate your power concern.
 P: 42 Thank you so much. I can't believe I didn't see this option before you mentioned it. I cycle to school everyday so this should be pretty easy for me to do. I'm going to visit a couple of scrap places tomorrow to see if I can get the parts.
 PF Gold P: 866 Maybe visit the prof on your way and make sure that his perception of the problem is the same as yours. In the original posting, the specification was 5 watts sustained over a period without human intervention. The prof then added a much shorted peak power alternative, without statement about using or not using human power. You can clearly get the peak power required, but if you have it from a human driven generator, does it pass muster? Parenthetically, you will get so much useful experience just by doing the messy work of making this lashup work that it won't matter what grade you get, you'll be way ahead in any case.
 P: 42 I saw the teacher today and he said that he has no problem with me going down this route. He was a little disappointed because he seemed to like my initial idea of using a TEG, and to be honest I feel that it's a more elegant solution compared to sweating on a bike.
 P: 42 I came across this just now: http://www.kickstarter.com/projects/...phany-one-puck It's designed to produce 5 watts under ideal conditions which means a fresh hot drink, if it can do that with a hot drink it could definitely do that with a candle or small flame couldn't it? This seems like no stirling engine that I've ever seen and the device itself is so small. It almost seems too good to be true. What do you think?
P: 589
 Quote by PraAnan ... It almost seems too good to be true. ...
Read the project's comments. One person posted some calculations and questions for the thermodynamics of their example scenario (5 watts from a cup of hot coffee placed on the device). His questions remain unanswered.
Mentor
P: 22,298
 Quote by PraAnan It's designed to produce 5 watts under ideal conditions which means a fresh hot drink, if it can do that with a hot drink it could definitely do that with a candle or small flame couldn't it?
Probably, yes.
 This seems like no stirling engine that I've ever seen and the device itself is so small. It almost seems too good to be true. What do you think?
5 W is not a lot of heat.

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