What is the maximum switching speed for electromagnet polarity?

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Discussion Overview

The discussion centers around the maximum switching speed for the polarity of electromagnets, exploring the theoretical and practical limits of how quickly the polarity can be reversed. Participants consider various factors influencing this speed, including the design of the electromagnet and the effects of inductance and hysteresis.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants suggest that there is a physical limit to how fast an electromagnet's polarity can be switched, influenced by the design and construction of the electromagnet.
  • It is noted that the time it takes for an electromagnet to turn "on" or "off" is not instantaneous and varies based on its construction, particularly the number of windings which affects inductance.
  • One participant mentions the potential for superconductivity to alter the switching speed characteristics.
  • Another participant introduces the concept of hysteresis as a relevant factor in the discussion.
  • A proposal is made to create positive and negative pulses to levitate a small object, emphasizing the need for rapid switching to minimize jolting effects.
  • Further suggestions include using a small magnetic field, shaping the magnetic field, or accepting a higher levitation height as alternative approaches to achieve levitation.
  • Experimentation with square waves and varying periods is mentioned as a method to explore the effects of switching speed.

Areas of Agreement / Disagreement

Participants express a range of views on the factors affecting switching speed, with no clear consensus on the maximum speed achievable or the best methods for achieving rapid polarity switching.

Contextual Notes

Limitations include the dependence on specific electromagnet designs, the influence of inductance and hysteresis, and the unresolved nature of the proposed methods for levitation.

Slakjak1215
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I'm not sure if this is in the right section but...Is there a limit to how fast the polarity can be switched on an electromagnet? If there is a limit then how fast can they be switched? Thanks.
 
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You can see that there has to be - if only because there is a limit to how fast you can physically throw a switch - i.e. signal generators do not generate an arbitrarily high frequency.

But I suspect you are more interested in the electromagnet end.

There is a limit there too - and it will depend on how it is made.

Basically an electromagnet does not come fully "on" the very instant it is switched on, and it does not go fully "off" when you cut the power. Toggle the power very fast and you'll get odd effects. What exactly happens depends on how the electromagnet is made.

To give you an idea:
http://ocw.mit.edu/resources/res-6-001-electromagnetic-fields-and-energy-spring-2008/chapter-10/10.pdf
 
Slakjak1215 said:
I'm not sure if this is in the right section but...Is there a limit to how fast the polarity can be switched on an electromagnet? If there is a limit then how fast can they be switched? Thanks.
Yes. In practice, the more windings you put on a given core, the longer it will take to reverse the current in the winding. More windings lead to it having more inductance.

If you went the superconductivity route, things might be different.
 
Slakjak1215 said:
I'm not sure if this is in the right section but...Is there a limit to how fast the polarity can be switched on an electromagnet? If there is a limit then how fast can they be switched? Thanks.

Google "hysteresis"
 
Okay well, ill just throw this out there, What about creating a positive negative pulse to levitate a very small object. This is what I am shooting for. The pulses would have to be incredibly fast to not jolt it very far.
 
Slakjak1215 said:
Okay well, ill just throw this out there, What about creating a positive negative pulse to levitate a very small object. This is what I am shooting for. The pulses would have to be incredibly fast to not jolt it very far.
Why do you want to both attract then repel the object? Wouldn't it suffice to repel it for a time, then switch off the field, assuming the magnet is positioned below the object?
 
... or just use a small field.
... or shape the magnetic field, or accept a high levitation :)
You could experiment by putting a square wave on an electromagnet and vary the period.
You may not need to go to critically small timings.
 

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