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Will a Faraday cage affect the efficiency of motors inside?

  1. Jul 11, 2015 #1
    "A Faraday cage or Faraday shield is an enclosure formed by conductive material or by a mesh of such material. Such an enclosure blocks external static and non-static electric fields by channeling electricity along and around, but not through, the mesh, providing constant voltage on all sides of the enclosure."

    Lets say I have both a motor, and Magnetic induction switch and then lastly a small neodymium magnet to trigger it, all inside a Faraday Cage. We know that the cage nullifies all charge and also magnetic field changes(which produce electric fields).

    Would this mean that the cage would act like a "damper" on the magnet and motor, thereby decreasing efficiency? It would have to since the motor is producing oscillating magnetic fields, thereby electric fields which will be moving the charges inside the cage. So some of the energy would have to be lost in momentary current. I am worried that the cage would affect a moving magnet, possibly making the magnetic induction sensor not trigger and if the energy lost into the cage from the motor is considerable.

    Are there grounds for a faraday cage affecting inside electrical equipment of all kinds, negatively? Or am I safe to just dump it all inside a very highly insulating faraday cage

    Thanks in advance, -Jarfi.
     
  2. jcsd
  3. Jul 11, 2015 #2

    Baluncore

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    A Faraday cage will not have a significant magnetic effect on things inside or outside.
    If it does not have mesh covered air vents it may reduce cooling and cause some items to overheat.

    Think of a Faraday cage as a mirror that reflects electromagnetic waves from both sides and so prevents fields crossing the cage wall.
     
  4. Jul 21, 2015 #3
    Preventing outside interference might cause a marginal (well under 1%) increase in efficiency. This will likely be more than offset by the inefficiency of getting power through the cage. (Longer wires, etc.)

    If the motor is near the cage walls, the winding fields might induce eddy currents. But so would any conductor near the motor. Again, the effect is tiny unless you work at getting the motor field lines to cross a conductor. Air gaps are effective at blocking magnetic fields (compared to core iron anyway).
     
  5. Jul 21, 2015 #4

    Nidum

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    90% of all power electrical equipment sits permanently in metal casings so don't quite understand the problem ???
     
  6. Jul 21, 2015 #5
    There's no problem. As I said, the effect is minimal.

    I was just being complete.
     
  7. Jul 21, 2015 #6

    berkeman

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    @Jarfi -- Can you say what the application is? Why do you need a Faraday cage at all?
     
  8. Jul 21, 2015 #7
    You wouldn't notice any effect. A Faraday cage, for the most part, shields the inside from external fields, and the outside from internal fields. The effect depends strongly on how fast the fields are varying and the frequency of radiation. Either way, the mechanisms of a motor aren't concerned with the field outside of the cage anyway, unless there was some enormously strong field present for some reason. If anything, a Faraday cage around a motor would benefit it by shielding stray fields.
     
  9. Jul 21, 2015 #8

    Baluncore

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    Probably the biggest potential source of inefficiency will be where power is passed through the wall of the cage. Both the active and the neutral conductor that carry power must pass through the same hole in the cage. If that is not done then the cage surface may form a magnetic short around the conductor with eddy current losses. When the conductor and it's current return pass through the same hole, their magnetic fields will cancel and so eliminate eddy currents.

    That is also true for signals. They should always pass through as coaxial cables or as twisted pairs.

    All signals and power passing through the cage wall will need some form of filter to prevent conduction of unwanted signals across the cage wall.
     
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