From what I remember about electricity generation, a varying magnetic field is used, either the magnetic field or the coil moves to generate electricity.

e = dB/dT


e = voltage induced

B = magnetic field

T = Time

Would more voltage be induced if both, the magnets and the coil, are mounted and geared to rotate at different velocity?

  • \$\begingroup\$ Well, you put more energy in (in the form of higher turning velocity), so you get more energy out (in the form of higher frequency). How does that relate to the "amount of electricity" though? \$\endgroup\$
    – Majenko
    Sep 13 '11 at 10:13
  • \$\begingroup\$ Induced voltage/EMF is a straight function of the rate of change of flux (atleast that is what I remember) e=dB/dT where B is the magnetic field, and T is the time. So if the flux change in the same period of time is greater, the generated EMF would be stronger ... potentially able to drive a larger load \$\endgroup\$
    – Everyone
    Sep 13 '11 at 10:42

In theory, yes. Practically, your idea makes no sense for the following reasons:

Your basic idea is right, faster variation of flux means bigger induced current, quite simply. Of course in reality this is way more complicated and there are a huge number of restraints. Also, the mechanical power input must always exceed the electrical power output. Not like you can magically create twice as much electrical power with the same input.

The idea is, having magnets pass changes in the field more often. Practically, this is done by giving the generator more poles. This means the same: more changes per revolution.

Rotating both magnet and coil at the same time is a bad idea for several reasons. In big installments, it is a challenge to rotate even one. Having both rotate coaxially adds even more of a challenge, so much so it is basically idiotic to try. How do you apply mechanical power to both, etc? In power stations, the generator is also set up in a way to have the coils standing fixed, avoiding the need to grab huge currents from a rotating part.

Also, power generation is generally synchronous, 50 or 60 Hertz, so it is inadvisable to change the amount of fluctuations per second. The setup for the generators is very much fixed.

  • \$\begingroup\$ While older generators were designed to directly generate 50 or 60 Hz, newer generators often generate power at varying frequencies, and solid-state variable-frequency converters convert that power to 50 or 60 Hz line frequency. \$\endgroup\$
    – davidcary
    Sep 13 '11 at 14:23

Induced voltage is proportional to the rate of change of magnetic flux, so to get more voltage, you can either use faster rotation, stronger magnets, or both.

Be aware that a number of things can go wrong with rotating a machine faster than its design spec. The insulation on the windings may not be able to withstand the greater voltage, and simply break down. The increased current that could result from having an increased voltage could cause thermal damage to the windings. Centrifugal forces on the rotor could cause outright mechanical failure.


Higher speed ( all else fixed ) increases the voltage ( better not to use the term "more electricity" which is open to many interpertations ). It does not matter if this is by turning one part or the other or both. Turing both is mechanically more difficult than just increasing the speed of one, and would be unusual. Power and current depend on other circuit elements but in any case energy will be conserved and values like torque may also change. ( torque could easily go down, attach a generator to a light bulb. Increase the speed, generally we think of the angular speed of a generator, until the light bulb "burns out". Under most conditions the torque will drop )


We all are aware that the power loss from mechanical energy of the rotor during the conversion of electrical energy in generator is also due to frictional forces on bearings, air resistance to rotor apart from conversion efficiency. Can we think a situation where magnets and rotors are fixed but the magnetic flux variation is brought in by a rotary curtain moving at high velocity between the rotor and the magnets. The curtain material blocks magnetic flux. It has rectangular slots at regular interval to allow magnetic flux to pass. There by changing flux to the rotor coil at high speed. I believe this can generate electricity with lower wear tear and low cost generators. Request comment on the feasibility.


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