Can a motor drive a generator which can produce power more than the power used by the motor to drive the generator?

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1139423

2026-08-12 12:10

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Claims about perpetual motion machines are always false because they ignore the inevitable losses of energy which must be overcome to make any machine operate so that it can do its intended work. Such losses mean that any machine, whether electrical or mechanical, must be supplied with more input power than it can convert into output power.

In the case of electrical machines there are many reasons for energy losses:

Bearing friction losses; "windage" losses caused by air having to be moved out of the way by spinning parts such as rotating armatures and cooling fans; magnetic hysteresis losses absorbed by eddy currents flowing in rotor armature and stator laminations; commutation losses in dc machines and slip ring losses in ac machines; excitation losses caused by the need to supply energy to the coils in the stator of a machine in order to magnetize it; general electrical resistance losses caused by the need to use energy to force electric currents to flow through the windings of any electrical machine.

Whilst engineers have found ways to reduce each one of those types of loss to a minimum, it is still a fact of life that no electrical machine can be 100% efficient. In the case of a motor, it will always require more energy to be supplied to it than it can convert to mechanical power. In the case of a generator, it will always require more mechanical power to be supplied to it than it can generate as electricity.

Some electrical machines have a power-conversion efficiency of up to 80% but most have efficiencies much less than that. If a motor and a generator were linked together to form a motor-generator set (the motor driving the generator driving the same motor) then, if both machines were as good as 80% efficient, that would mean the combined efficiency of the system of would only be .8 x .8 = .64 i.e. 64%. In other Words, to keep the motor-generator set running, additional power equal to at least 36% of the motor-generator set system's own power would need to be supplied from an external source.

Those facts make the set-up described in the answer to this question shown below pure nonsense. Period.

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