Generating Electricity: Understanding the Basics

[MattVonFat]

Hi,

I saw a TV program where a guy made a hand powered electric generator thing, where a magnet is spun inside of many coils of wire. I remebered from high school physics doing this and started wondering why you can't feed the elecricty you produce into a motor to spin the magnet for you giving a sort of unlimited supply of electricty.

I know there's a good reason why that doesn't work but I don't actually know what it is. I had asked a friend of mine who's studying to become an electrician and he gave me an explanation but it didn't make sense (I don't even think he was quite sure, it was just something the teacher mentioned in class).

Just something I'm curious about.

Thanks,
Matthew

 

[Pengwuino]

Well, in the most basic sense, conservation of energy is the problem.

If you put a certain amount of energy into a generator, it can only produce that same amount of energy in electricity or less (less in reality because energy is lost to friction). Then if you put that energy produced back into the motor, you can only get that same amount of power back or less. All your power is going back into the motor to keep the thing running

 

[bobbytkc]

i think without citing the conservation of energy and the 2nd law of thermodynamics, the simple explanation is that when you spin the magnet, there is an electromagnetic force pushing back in the opposite direction to the direction you are spinning.

So if you just add a magnet to a motor to spin the magnet to generate electricity, it is possible, but the effect is similar to braking, and in a car, you would like to speed up, not slow down.

In fact, hybrid cars use this concept really well, when you slow down, they generate electricity to be stored, but when you speed up, they cut out the magnet and allow you to accelerate normally.