Do concentric coils steal power from one another?

  • #1
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Summary:
Learning about power generation using magnets and coils, wondering about more complicated scenarios
The amount of power generated by a coil in a changing magnetic field is determined by the area perpendicular to the field, the field strength, and how quickly those values change over time, and is multiplied by the number of loops in the coil.

But that made me wonder what would happen if one coil was placed inside of another. Would you get more power out of that set up? Or does a single coil already get the maximum amount of energy from the magnetic flux it encloses, so placing a coil inside is like placing one solar panel on top of another?

As a side note, I was also wondering if a stack of unconnected metal rings would work the same as a single coil?
 

Answers and Replies

  • #2
Baluncore
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The amount of power generated by a coil in a changing magnetic field is determined by the area perpendicular to the field, the field strength, and how quickly those values change over time, and is multiplied by the number of loops in the coil.
No, it is the voltage induced in the coil, not the power or energy.

The primary and secondary windings in a transformer are effectively several loops lying over each other, sharing a common field.

If a current flows in a secondary coil, that current will change the total magnetic field.
 
  • #3
Tom.G
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Summary:: Learning about power generation using magnets and coils, wondering about more complicated scenarios

But that made me wonder what would happen if one coil was placed inside of another. Would you get more power out of that set up? Or does a single coil already get the maximum amount of energy from the magnetic flux it encloses, so placing a coil inside is like placing one solar panel on top of another?
You are good until the <total current drawn> times the <number of turns> creates a magnetic that is high enough to cancel the field from the magnet.

Also, as you draw more current (power), it gets more difficult to move the magnet in relation to the coil(s) (or the coils in relation to the magnet). This is because the electrical power is supplied by the mechanical power.

Bicycles used to have a headlight powered by a generator driven by the front wheel. You could definitely feel the harder pedaling required with the headlight on!

You can sometimes notice this in a car that is idling. Try it with the headlights Off then On, the idle speed changes. (This works at least in older cars, the computer in the newer cars keeps the idle speed constant. The sound of the engine may change in newer cars, especially those with a small engine.)

Cheers,
Tom
 
  • #4
Charles Link
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You might find this thread of interest, and look also at post 12 and the "link" there.

https://www.physicsforums.com/threads/i-dont-understand-transformers-how-to-apply-them.1002399/

One interesting feature about transformers is that there is a power balance between the primary and secondary, and that when the seconday windings draw a current, the primary windings respond in such a fashion that there is little or no change in the magnetic field strength inside the transformer core from the case of no current in the secondary to the case of where the secondary is drawing a significant current. This is expressed by the formula ## |N_p I_p|=|N_s I_s| ##. This can also be viewed as MMF's (magnetomotive forces) canceling between the primary and secondary, with the remaining ## N_p I_{po} ## of the primary is what determines the magnetic field in the transformer core.

See also

https://www.physicsforums.com/threads/waveform-of-classic-electromagnetic-induction.1003690/
for a discussion on what is a simple ac power generator using a bar magnet and a coil of wire. It's a lengthy thread, but there are some interesting experimental results as well as theoretical calculations that compute the waveform towards the end of the thread.
 

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