# Foo - Explain to me why this won't work.

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Ted Danson
07-26-09, 01:09 AM
I was thinking about how to generate electricity from magnets. This is obviously a basic drawing but why couldn't you run a setup like this to gain electricity.
The magnets push off each other due to their polar fields and spin around on a fixed axis (purple point)
This fixed point is a rod that is connected to a generator.
The green arrow shows the direction the "fan" spins.

I don't exactly know how to explain how it works because it is late at night but I drew a picture to help;)

http://i28.tinypic.com/2yugi95.jpg

jschen
07-26-09, 01:58 AM
You'll generate electricity, but not as much as the energy you put into it. If you have to generate the wind from a fan, then forget it. You've got a fundamental thermodynamics problem.

If the wind is coming from some other energy source that you otherwise wouldn't have used, then yes, you can generate electricity. However, the magnets are exerting a force on each other in both directions. You'd do just as well with non-magnetic blades.

jschen
07-26-09, 02:04 AM
Oops... I was reading your drawing wrong. If you start at the right point, you might get the system moving a bit. But it will just wobble back and forth, since the acceleration in one direction radially is matched by the acceleration in the opposite direction in the mirror image position. (Yes, you can tilt the non-rotating magnet, but that merely changes where the equilibrium point is. It doesn't change the existence of such a point.) So there is nothing to be gained, and only frictional losses.

Furthermore, if you're generating electricity, then there is an additional resisting force since you're taking energy out of the system. Therefore, the system will rapidly settle at a stable position.

Ultimately, all this analysis can be simplified by simply realizing that no matter how cleverly you set up the system, you still can't get more energy out of it than is going into it.

c0urt
07-26-09, 02:12 AM
it is an actually law, you have to put power in to get power out, it it's simplest form.

it may or may not be bernouli's principle, I need dinner.

what jchen is write I want to also add.

Ted Danson
07-26-09, 02:19 AM
I don't understand how you are putting any work into it though. Magnets repell?

darksiderising
07-26-09, 02:37 AM
Read up on magnets on wikipedia, particular this section:
http://en.wikipedia.org/wiki/Magnet#Magnetization

The magnetic forces would cancel each other out and you would have a net-zero force.

c0urt
07-26-09, 02:41 AM
it will get stuck between two magnets with a reason and just wobble. both magnets will repel in opposite directions with out a reason to repel from the magnet between them.

or someone to push it every so often, once again power input. If you were to put it in a power circle and make the outer magnet an electro-mag and have the power coming from the inner ring, you would still need need a way to make it pulse initially.

too late at night for diagrams

c0urt
07-26-09, 02:42 AM
Read up on magnets on wikipedia, particular this section:
http://en.wikipedia.org/wiki/Magnet#Magnetization

The magnetic forces would cancel each other out and you would have a net-zero force.

awesome, thanks great input

c0urt
07-26-09, 02:43 AM
oh, and normal magnets over time a north side ran against a south side, is going to make the south side north. Or if you are really lucky, an east side messing every thing up.

Snicklefritz
07-26-09, 03:05 AM
the real thermodynamics problem:
(1) you can't win
(2) you can't break even
(3) you can't get out of the game

ilikebikes
07-26-09, 07:05 AM
I have a working perpetual enegy engine, but I'm not telling you about it!....Oops! :twitchy: ;)

DannoXYZ
07-26-09, 04:53 PM
I don't understand how you are putting any work into it though. Magnets repell?Yes, but the moving magnet has to get into position to be repelled by the stationary magnet. The problem is that BEFORE it gets into that position, it will be in an ATTRACTION position. Imagine rotating your propeller anti-clockwise about 10-15 degrees. Before it can get into the repelling position, it will be pulled back by the stationary magnet and all rotation will stop.

What you've got drawn is very similar to a rotary piston airplane engine. Imagine each magnet as a piston pushing up and down in each cylinder. In order to keep the system going, you have to ADD energy to the system, such as an exploding air-fuel mixture.

In your system, you have to ADD more energy to break the rotating magnet away from the attraction position as each magnet spins past the stationary one. Where is this energy coming from?

Also you want to draw actual magnetic-field lines on the bar magnets. They aren't linear, but wrap around the ends.

http://i206.photobucket.com/albums/bb103/ken_winstonitoh/ken4.png

mlts22
07-26-09, 05:05 PM
When I started college, I had the same exact idea for an invention, expecting the repelling force of the magnets to keep this setup spinning indefinitely.

However, the same answers as posted above is what would happen. End result will be the contraption will spin a bit, vibrate for a bit, then stop because the repulsive force of one magnet cancels out the attractive force of another as it spins.

skijor
07-26-09, 05:32 PM
1st law of thermodynamics (http://en.wikipedia.org/wiki/First_law_of_thermodynamics)

gman26
07-26-09, 05:56 PM
I always wondered if there was a way to perpetually provide power to a battery running an electric car. It seems if you had a generator on each wheel and alternating battery supplies you could charge one battery while the other powers the car. Too good to be true?

jschen
07-26-09, 06:02 PM
I always wondered if there was a way to perpetually provide power to a battery running an electric car. It seems if you had a generator on each wheel and alternating battery supplies you could charge one battery while the other powers the car. Too good to be true?

Not a chance. Using one battery to charge another one is not going to gain you more usable energy than you started with. If it did, the world's energy problem would be trivial to solve.

couch_incident
07-26-09, 06:03 PM
I nominate you for the 'Coolest Poster on Foo' Ted. Keep up the good work. Now, if you engineer a couch that does the laundry and cooks, you'll have a friend for life! Start working on that now.

Couch

late
07-26-09, 06:12 PM
Take your gadget and weld onto a trianagular frame. Put your bike on the frame and pedal. Hook some wires up to your toaster.

Pedal real fast.

Hickeydog
07-26-09, 06:12 PM
I always wondered if there was a way to perpetually provide power to a battery running an electric car. It seems if you had a generator on each wheel and alternating battery supplies you could charge one battery while the other powers the car. Too good to be true?

But what is providing the energy to turn the wheel that is charging?

Alfster
07-26-09, 06:13 PM
I nominate you for the 'Coolest Poster on Foo' Ted. Keep up the good work. Now, if you engineer a couch that does the laundry and cooks, you'll have a friend for life! Start working on that now.

Couch

gman26
07-26-09, 06:16 PM
Not a chance. Using one battery to charge another one is not going to gain you more usable energy than you started with. If it did, the world's energy problem would be trivial to solve.

Not using another battery to charge a battery, using the spinning wheel to charge a battery. Then when the battery is charged, switching over to it to run the car. Meanwhile, the other battery is running the car.

jschen
07-26-09, 06:18 PM
Not using another battery to charge a battery, using the spinning wheel to charge a battery. Then when the battery is charged, switching over to it to run the car. Meanwhile, the other battery ios running the car.

The battery is what ran the motor to spin the wheel. You're still ultimately charging one battery by taking energy from another battery.

gman26
07-26-09, 06:24 PM
The battery is what ran the motor to spin the wheel. You're still ultimately charging one battery by taking energy from another battery.

hmmm... why is this so difficult?

jschen
07-26-09, 06:25 PM
It simply can't be done.

gman26
07-26-09, 06:29 PM
It simply can't be done.

"can't be done" ??

That's not the spirit that got us where we are today. Maybe in another life.

jschen
07-26-09, 06:33 PM
Scientists and engineers push boundaries, but we also have to be aware of the limits that we're working against. Naively dreaming does not produce progress. Carefully analyzing the situation and attacking carefully selected problems is what produces progress.

jschen
07-26-09, 06:36 PM
To elaborate a bit further, the fundamentals of thermodynamics is basically a counting game. It's simple math, as one can learn in statistical thermo, and the laws of thermodynamics are quite secure. Trying to defeat thermodynamics is one of few things in the universe that I feel comfortable in saying is a hopeless waste of time.

x136
07-26-09, 07:08 PM
Not using another battery to charge a battery, using the spinning wheel to charge a battery. Then when the battery is charged, switching over to it to run the car. Meanwhile, the other battery is running the car.What you probably aren't taking into account here is the generators introduce drag.

In fact, this is exactly how the regenerative braking in Toyota's Hybrid Synergy Drive based cars (Prius, etc) works. The power from the turning wheels is fed into a generator to replenish battery power, which in turn slows the car.

Were you to run a generator from the wheels all the time, you'd have to put much more energy into making the vehicle actually move, since the generator would be sapping so much power from the act of moving the vehicle. Therefore, the more power you recover from the turning wheels, the more you have to put in in the first place.

couch_incident
07-26-09, 07:11 PM

I'm screwed up Alfy. But you knew this allready.

Sofa King

skijor
07-26-09, 09:37 PM
http://www.hulu.com/watch/21710/the-simpsons-stir-crazy-kids
"In this house we obey the laws of thermodynamics" :p
http://images.kaneva.com/filestore0/250971/228131/angry-homer_la.gif

Ted Danson
07-26-09, 11:10 PM
I understand now. Thanks guys.

DannoXYZ
07-27-09, 01:08 PM
Not using another battery to charge a battery, using the spinning wheel to charge a battery. Then when the battery is charged, switching over to it to run the car. Meanwhile, the other battery is running the car.Here's where we have to take qualitative abstract ideas and put it into practice and measure quantitative real-world values. We need to apply numbers to ideas because that allows us to accurately model what happens in the real-world.

So... let's say have a car of X-lbs with Y-drag from wind-resistance traveling at Z-speed. Under XYZ-conditions we have four components:

1. storage battery that's providing power
2. electric motor that's moving the car
3. generator that's being spun to generate electricity while the car's running
4. 2nd battery that's being charged by the generator

Let's follow the path of energy from the start to the end:

1. 1st battery outputs 933 watts of energy

2. electric motor is 80% efficient and puts down 746 watts of energy to the road

3. let's say only 1/2 of this energy is used to drive the car and 1/2 of this energy goes to driving the generator. So 373 watts (0.5hp) goes to moving the car and 373 watts goes into driving the generator. The generator is 80% efficiency so 1/2hp spinning it allows it to create only 298watts.

4. 2nd battery is charged by generator at 298 watts

So as you can see, the recovered power 298 watts from extracting energy from the moving car is only a small percentage of the 933 watts needed to drive it. It's a lossy system that will always require adding power from an external source to keep going. So in this case, by the time the 1st fully-charged battery has run out, the 2nd battery is only charged to 32%. If you swap batteries and use the 2nd battery to drive the car and charge the 1st one, by the time the 2nd battery is run down, the 1st battery will only have been recharged to 10% of its initial value.

Even in the extreme case of applying ALL power from the 1st battery+motor to the generator+2nd battery so that the car doesn't move at all, you'd expend 933watts to get back only 597watts going into the 2nd battery (933 * 80% *80%). So using the motor to drive the generator to charge the 2nd battery will only charge the 2nd battery to 64%.

This isn't even taking into account frictional losses from the wheel-bearings, drag from wind-resistance and other power-sapping areas.

This example shows why you can't sit in a sailboat and blow on the sails to get it moving...

gman26
08-03-09, 10:36 AM
I see.

Rob P.
08-03-09, 04:12 PM
I have a working perpetual enegy engine, but I'm not telling you about it!....Oops! :twitchy: ;)

Oh, you must be talking about fossil fuels. It's the ONLY perpetual energy system I know of that seems to function.

We take a barrel of oil out of the ground. Half is usable as fuel. That half-barrel powers ALL of our cars, and generates A LOT of our electricity. Some of that electricity is used to run the pumps which suck the oil from the ground which we put into barrels. Half of which is usable as fuel. . .

kila kila kila
08-03-09, 04:18 PM
That's funny because during summer classes after my first year of school, I also "invented" pretty much the exact same little impossible motor you and mlts22 did. Obviously, it never went anywhere...

kache_98
08-03-09, 04:48 PM
it is an actually law, you have to put power in to get power out, it it's simplest form.

it may or may not be bernouli's principle, I need dinner.

what jchen is write I want to also add.

It's actually the conservation of energy law, although bernouli's principle is derived from it. Bernouli's states "that for an inviscid (no viscosity fluid) flow, an increase in speed occurs simultaneously with a decrease in pressure". I.E. Airplane wings, sails, ect.

wristwister
08-03-09, 05:17 PM
Hey, I don't know nuthin 'bout this thermodynamics laws stuff, but a few years ago I hooked my car's alternator directly to the starter. I give it a push and I can drive all day just on the starter power! I haven't bought gas for that car in years. I keep this hush-hush 'cause ... you know ... them big oil companies would probably take me out if they knew about this.

Nota
08-03-09, 05:23 PM
Oh, you must be talking about fossil fuels. It's the ONLY perpetual energy system I know of that seems to function.

Uhhh...fossil fuels = "perpetual energy"??? WTF?

....you do understand what "perpetual energy" means, don't you? ...just askin

It (fossil fuel) is a finite resource; one that gets consumed in the combustion process, while producing energy from it. It is not sustainable. ie..Solar, Wind, Rain, Tidal, Geothermal, perhaps, but not Fossil.