# How much heat/friction can small magnets really make?

1. Jun 12, 2015

### Infinityze

Suppose you had a rotating magnet, about the size of a penny, about how much friction/heat could it make in watts?

2. Jun 12, 2015

### davenn

hi there
welcome to PF

friction and heat generated from it requires it to be "rubbing " against something
it wouldn't be any different to a plain metal disc .. being magnetic is irrelevant

Explain more clearly what you are trying to discover

Dave

3. Jun 12, 2015

### Infinityze

Thanks!

I see, is there like a formula or relationship between friction and heat produced? I'm looking for a way to produce heat (and then electricity with a thermoelectric converter) using friction created by a magnet (why its a magnet is not important for this discussion, but it just is :P).

4. Jun 12, 2015

### davenn

because you original post was very incomplete and in the way stated using a magnet was irrelevant

have you pasted that Q into google to see what results you get ?

5. Jun 12, 2015

### davenn

why don't you just spin the magnet in a coil like a normal generator ? .... would be much more efficient ... ie ... wouldn't have the huge energy losses

6. Jun 12, 2015

### Infinityze

Sorry for being vague earlier, but I guess this is where the size comes in. I want it to be as small as possible, like the whole thing would be a few centimeters or inches tops.

Edit: I also don't have much of an electrical background so if there's a different way to do this while keeping it small, i'm open to suggestion. Just need it for a side project.

7. Jun 12, 2015

### davenn

do some googling on electrical generators and alternators

8. Jun 12, 2015

### Drakkith

Staff Emeritus
You're still being vague. It would greatly help us help you if you told us exactly what you were trying to do. I'm not certain why you want to generate friction by rubbing a magnet. Are you aware that heating a magnet past a certain temperature causes it to lose its magnetism?

9. Jun 12, 2015

### Infinityze

Okay, I did and it helps a lot. Let me pose my problem this way, is there any way I can make one magnet produce mechanical energy once it is in range of another (perhaps through friction)?

10. Jun 12, 2015

### Drakkith

Staff Emeritus
Magnets don't produce energy, they only help convert it from one form to anther. For example, magnets used in generators convert mechanical energy to electrical energy. There are multiple ways of producing electricity on a very small scale. To help find the best method we need to know the details of what you're trying to accomplish or we aren't going to be able to help you much.

11. Jun 12, 2015

### Infinityze

Okay now that I have a better picture, want to power a generator from a distance (at least 10-20 ft) automatically. I was thinking maybe two magnets could work, if one could make the other generate mechanical energy. Would this work? If not, is there something else that would?

12. Jun 13, 2015

### Drakkith

Staff Emeritus
Without some kind of mechanical linkage between the generator and the source of mechanical power, no. Not at that kind of distance. Not without having huge magnets that outweigh and outsize the generator by several orders of magnitude. When I worked on cruise missiles for the Air Force, our missiles had an electric fuel pump which turned a shaft attached to a disk magnet. The entire pump, shaft, and magnet were outside and isolated from the fuel in the tank, but on the other side of the wall there was a second, mechanical pump inside the tank that was turned by the magnet of the first pump. But the separation distance was very small. Inches at best, not feet.

The main reason for this is that the strength of a magnetic field falls off as 1/r3, which is even faster than the 1/r2 drop off in the electric or gravitational fields. (So if you double the distance from the magnet, the strength of the field is 1/8th as strong as it was at the original position)

The only way I can think of to power the generator without having a physical linkage would be to have a motor-generator instead of just a generator, with the motor side powered wirelessly from your master power source. But this would be super complicated and horribly inefficient.

A motor-generator is exactly what it sounds like. An electric motor attached to a generator. The motor turns electrical power into mechanical power, which is then converted back to electrical power by the generator. Very nice for high-power conversion of one type of electrical power into another type. For example, we had several large motor-generators where I worked in the Air Force that converted 60 Hz mains power into 400 Hz power used in powering up missile electronics for testing.

How much power are you looking to get out of this generator? If it's only a very small amount there may be other options we haven't considered.

13. Jun 13, 2015

### Infinityze

Interesting, would this be able to stay small-scale or would it get too big? I'm looking to get around 5-10 watts out of it.

14. Jun 13, 2015

### Drakkith

Staff Emeritus
How about a solar panel and a focused light source? Simple to set up, no moving parts, works night and day.

15. Jun 13, 2015

### Infinityze

That might work, but I want to be able to put the motor generator inside another machine. Do things like small infrared panels exist to go through objects? Things that would be able to take something like a focused infrared source and use the motor generator to create electrical energy?

16. Jun 13, 2015

### Drakkith

Staff Emeritus
Well, what is your generator powering to begin with?

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook