Using man-power to turn massive generator

robotbender

Hi guys, my first post! I really enjoyed reading this thread, it's funny and intelligent - a great combination.

I found this site trying to work out the power a person can generate (not just consume).. you know how it is, ideas, nothing to do, calculator itching for numbers..

My physics is a little rusty so I really enjoyed reading this post. It looks like a few keen minds are as rusty as me and the perhaps improper use of some of the terms used is caused by not fully understanding them. Things like what power, leverage or a KW/h actually is.

What roused my interest is the 200W a 'reasonably fit' person can produce. Am I right to think you mean this in a calorie/joule - enery ratio per hour?

An average althetic male will use about 1700 cals a second (612Kcal hour) playing squash - intense physical exersion. A watt is the SI derived unit of power, equal to one joule of energy per second. Ergo 1W = 1J/s. 1 calorie = 4.18400 joules (4.2W) which equates to 7112.8W or about 7Kw second for the squash player. As Watts and Joules are time oriented, we can't multiply this out to infer a human will generate 25MW/h! I understand this healthy person is capped out at 7Kw/h (I said I was rusty).

I can only understand from tmoney's original question (also with reference to Giesick's Force Needed to Turn Generator at Maximum Output post) that from 6 hours (hard labour a day) would equate to (7Kw/h * 6 hours) 42KW/h day.

I see one obvious flaw (aside from my maths) in the fact that we would expell 7112.8W a second just to do the work so any device used to capture the energy would be less efficient. Some of the most efficient alternators are about 80%, but it's interesting to imagine how much real-power can be produced from pure grunt. In honesty my interest comes from thinking the gym in itself is a waste of time and quite literally - energy. It would be interesting to save it up and use it at home squashing the electricity bill, staying fit, or do I just need to get out more?

dE_logics

"Could man-power through the use of massive gears, be used to turn a very large generator.?"


You're gonna require cheep labour fir that...so why not go to India to try it?

Considering the efficiency of this thing is not 100% you're gonna require men so as to generate this much amount of energy in a limited time interval.



Feed them well! :)

dE_logics

The image says not for public use.

mabs239

No body discusses the man's old friends, Bulls and Elephants. What if they are substituted as prime movers? I hope it would dropm the workers figures in million to some less number. Other than that it would help save wild life.

russ_watters

Welcome to PF.

A calorie/joule doesn't make any sense to me. No, 200W is 200W. It is the power that they generate (ie, by pedaling a bike). You have an extra zero in there: 612000/3600=170 cal/s. Yes. Now you are mixing power and energy. 1 cal is 4.18 J or 4.18 w-s. Same error carried forward: 170 cal/s *4.18 J/cal = 710 J/s or 710 W You're realizing there is a time element there, but using it incorrectly. There is no such thing as a MW/h or KW/h. MW and KW are already a rate, in terms of seconds. To get power, you multiply by time. Energy from a power plant is measured in KWh or MWh, which is killowatt-hours or megawatt-hours: 1000 and 1000000 J/s-h.
Again, these units are wrong and the decimal error is carried forward: 700 W for 6 hours is .7*6 = 4.2 KWh per day.

markplans2

I don't take anything for granted, and I don't believe everything I am told. I like to put things to the test. So does anyone have an idea, for some way to test this theory?

I would think using a controll, of one man, healthy enough to turn a turbine or generator of
some kind, to see how much energy he can produce by turning a lever let's say, would be simple enough. however
Not all men are equall.
And I don't like the idea of using a bycicle, to see how much energy is produced. (you are only using your legs)

what I would like to see, is a small wind turbine on the ground, positioned so blades were parellel to the ground, and see how many men it would take to turn the blades of the turbine.
Unless someon has a calcutlon they coudl run to show that this would be an impossible act?

I would even be up for planing an event at some location, gathering some able bodies up,
and testing this theory.

russ_watters

Any elliptical machine will use both your arms and legs and already tells you the power output. If you don't believe it you can hook it or a bike up to a generator. There is no need to get convoluted and complicated.

I'm not sure you will get many people who don't believe what their exercise bike is telling them so you may need to just do this yourself.

markplans2

I hear what you are saying. I could measure what my own output would be. But my problem with this theory is that we are bassing these calculations, on what one man can do. I am terrible at explaing these things, but I will try:
I can peddle my bike at a maximum sustained speed of 17 miles an hour, on flat ground.
In our equations, we are assuming that if we add another man to the bike, we can now go 17 x 2 = 34 miles an hour.
But this is not true. Haveing a tandum bike does not meen you go twice as fast.
The reason being is you are limited by the bike itself. the gears are too small, there is greater wind resistance, ect.

In essence, what we would have to do is make the the gears bigger.

Let's say you have (2) men in a room with a stationary bike. no wind. no road friction.
It would stand to reason that (2) men, could move the same gear, that is twice the size of the gear, that a single man can move.

What I am saying, is that (2) men could move a gear that is 2 1/2 times the size.
Maybe even more.

QuantumPion

It's possible that the human body could be more efficient at pushing a lever with high force at low speed (I have no idea if this is the case). However the maximum product of the two (force * speed = power) is still limited by what the average human body can continually produce due to physiology.

brainstorm

The most efficient way to harness human-generated energy, imo, is to put people in warm clothes when it's cold and have them do exercise or labor to warm themselves. I have experimented with this and found that I can live comfortably as low as 40F with a warm coat and hat/cap. Compare the amount of calories/joules/btus necessary to bring a house from 40F to 65F and the amount your body needs to generate to keep you feeling toasty in a sweater or coat with hat and gloves? If you're doing exercise or labor, you might even need to shed some of the clothes.

Maroki

Hallo every one, I was very surprised and happy at the same time to find out there is a Forum investigating about this interesting issue on which I’m thinking since some time. For this reason I just got registered and wander if we could continue to analyze and expand the subject more in details, scientifically in all aspects related to the use of man-power to produce electricity, not only for prisoners but also for poor communities where having access to few kWh of electricity it could mean much more the better welfare.
I personally would be very interested to study the idea of introducing this opportunity into prisons, (that it shouldn’t be an obligation to my opinion) I’m convinced there would be a number of interesting advantages, such as:

1. producing something (you said 4-5 kWh, maybe by using a more efficient equipment it could be increased ?) it would be good for the environment and the society while reducing the prisoner public cost.
2. while the man is physically at work pedaling, with legs and/or even with arms, at the same time he could still use the brain and apparently without disturbing his concentration with good result for both mind and body activities.
3. the activity is proved of being an important health factor, “Mens sana in corpore sano” (healthy mind in healthy body) there should be experiments already done that can tell us more about it.
4. More chance for him to understand how to behave in order to reduce his penalty, to learn more about social relation and how to plan his future after being released.
5. He will be, mentally and physically busy in doing something good for him self and the society, reduce stress on him as well as on the every one else around him and feel less useless
Many other positive aspects could be listed if you like……
Thanks for your attention and Regards
Maroki

pallidin

Jeez, just use hamsters or rabbits.
Or maybe horses... horsepower :)

Maroki

Well… you missed to mention the donkey-power or the mule-power….which, you should know, are the most efficient among them all, but in all cases, palladin…..instead of funny nonsense why not opposing scientific or at least reasonable questions, if you have any?

pallidin

Well... human powered generation of usable force has been around for a very long time.
On a low-scale level, say, a hand-crank radio or flashlight all is good. Or paddles for a canoe.
On a scale exceeding this it becomes functional ridiculous; given current technological alternatives.

DaleSpam

It wouldn't really be good for the environment. Humans generate a lot of CO2 when producing mechanical work, and the fuel for humans requires a lot of fossil fuels to produce, distribute, and prepare.

QuantumPion

Yeah you would be better off just burning food in a boiler to run a steam turbine then feeding it to people to do manual labor. :p

Maroki

a lot of CO2, when producing mechanical work?…yes ok, but how much?
maybe you do know that before the industrial revolution, before carbon fossil fuel came into the scene I mean, a farmer or one man could produce four (4) calories per each calorie spend in his work;
and maybe you do know also that thanks to the carbon fossil fuel now one man can produce many times more finished products then before (hundreds or even thousands times) but for each calorie it is burned ten (10) calories.
How much of CO2 is producing this type of mechanical work?
Let us go into numbers if possible please.