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If I have $x$ amount of electrical energy and convert that into mechanical energy using an AC Motor, and then convert that energy back into electric using an AC generator, will the amount of energy remain about the same?

If yes, then since the number of coils is proportional to the magnetic field and the magnetic field is proportional to the current.

Using the same combination of motor and generator, Can I convert the $x$ amount of electric energy into mechanical using an AC motor and then by doubling the number of coils in the generator (or rather the solenoid) thus making the magnetic field stronger and ultimately getting a stronger current, can I double the current?

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  • $\begingroup$ This question appears to be off-topic because it is about perpetual motion $\endgroup$
    – Carl Witthoft
    Commented Oct 15, 2014 at 14:05
  • $\begingroup$ @CarlWitthoft: I do not see anything about perpetual motion here. Looks more like a question about transformers to me. $\endgroup$
    – Kyle Kanos
    Commented Oct 15, 2014 at 14:43
  • $\begingroup$ @KyleKanos mebbe - I read it as feeding the mechanical energy back to the same or similar AC motor/generator to reclaim the original " electrical energy" $\endgroup$
    – Carl Witthoft
    Commented Oct 15, 2014 at 15:19

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A motor-generator can be used to convert electric power from one voltage x current combination to another voltage x current combination. Such systems have been used, and are sometimes still used, for exactly this purpose. One advantage is that a large flywheel can be added to the shaft, effectively low pass filtering the average power. This can be useful for eliminating spikes and short term fluctuations. Such a system can also easily be made so that the input and output are electrically isolated from each other. Yet another advantage is that either side can be AC or DC independent of the other, and if AC, need not be the same frequency or be phase-locked.

However, no power conversion system, including a motor-genrator, can produce more average power out than in. In reality such systems all have losses. Let's say for example that the motor and generator are each 90% efficient (good but achievable), then the overall motor generator will be only 81% efficient. If you put 1 kW in, you only get 810 W out. The remaining 190 W will be dissipated as heat in the coils, the bearings, etc.

You can change the combination of voltage and current, but the voltage x current product out (power out) can't exceed the voltage x current product in. For example, using the overall 81% efficiency from the example above, 10 A at 100 V in could yield 8.1 A a 100 V out, or 68 A at 12 V, or 810 mA at 1 kV, etc.

There is no free lunch (or energy).

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  • $\begingroup$ Fine but even after converting electric to mechanical and having a loss of 10%. While converting mechanical to electric, if you use a stronger magnetic or turn the coil over and over which will make the magnetic field stronger, thus producing more current. In theory, you should get about double the amount of current if you have the coil turned twice. However for practical use, it may be lower. $\endgroup$
    – Abhishek Mhatre
    Commented Oct 16, 2014 at 10:28
  • $\begingroup$ @Abhis: As I said, it is quite possible to make a higher current out than in, so it's hard to tell what the point of your comment is. I even gave a example with 10 A in and 68 A out. If this is all you are after and both input and output are AC at the same frequency, then a transformer would be much simpler and can be made more efficient for the same cost. $\endgroup$
    – Olin Lathrop
    Commented Oct 16, 2014 at 12:39

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