# Motor turning a generator

1. May 11, 2007

### ajsingh

Imagine that we have a motor running at some power. Now, the spindle of this motor is connected to the axis of a generator, so the rotation of the motor spindle will rotate the axis of the generator. In an ideal situation (no friction, back emf, etc. and using similar number of turns of a coil having the same area and same magnetic field as that of the motor), will the generator produce the same power as the input?

Now imagine I increase the length of the spindle of the motor, and attach a second identical generator next to the first one, so both the generators will rotate together at the same frequency. In this case, will both the generators produce equal amounts of power which is equal to half the input power?

Just a random situation I was discussing with a friend the other day. Any help would be appreciated.

AJ

2. May 11, 2007

### chroot

Staff Emeritus
Sounds reasonable. As you keep loading down the motor with a larger number of generators, its rotational speed will necessarily slow down, though.

- Warren

3. May 11, 2007

### ajsingh

So that means, when I add a second generator to the system, the rotation speed of the first (and the second) will become equal to or less than half of the rotation speed of the first generator connected alone? Is possible that the rotation speed might end up infact being more than half for both the generators than that of the first generator alone?

Example
1 Generator alone : 5000 rpm
2 Generators together : 3000 rpm each

Will the principal of conservation of energy be violated in such a case? And what does actually reduce the rotation speed of the generators?

AJ

4. May 11, 2007

### chroot

Staff Emeritus
It depends on exactly how your generator's output power depends on its input angular frequency. If we assume that it's linear, then doubling the load on the motor must halve the angular frequency. If it's non-linear, then sure, your numbers could be possible.

No matter what the relationship is, though, the conservation of energy can't be violated.

- Warren

5. May 12, 2007

### ajsingh

Thanks Warren.

Imagine we assume that the output power depends linearly. Why does the angular frequency reduce? What do you mean by load?

6. May 12, 2007

### FredGarvin

The "load" is the electrical demand placed on the generators.

7. May 14, 2007

### brewnog

The generators will produce power to match whatever load is put on them (up to a limit).

There's no reason why they'll automatically share the load out equally between them.

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