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Registered Member #8497
Joined: Tue Dec 04 2012, 06:24PM
Location:
Posts: 74
This is a purely theoretical question.
In a simple inductor / coil once the current rise has ceased (at the peak), how does the energy stored in the magnetic field collapse? Which polarity end of the coil will be +/-?
Registered Member #509
Joined: Sat Feb 10 2007, 07:02AM
Location:
Posts: 329
The current keeps going in the direction you made it go to begin with, voltage applied to the inductor determines dI/dt, and forcing a dI/dt determines the voltage generated by the inductor. As for polarity, since current doesnt change directions, and energy is leaving the coil instead of being put into it, the voltage changed direction.
Practical example just for clarity, take a 12v automotive relay, apply 12v across it, disconnect the positive lead of the coil quickly, and since the other lead is still grounded, the lead that was hooked to the +12v will swing negative, possibly by quite a lot. Hence why anti-parallel diodes work.
Semi-related anecdote. I had a 24v solenoid that apparently had a built in catch diode, because when you cut the power on it it took it a few seconds ( ! ) for the plunger to come back out. And it wasnt sticking either, make sure it was moving freely.
Registered Member #5258
Joined: Sun Jun 10 2012, 10:15PM
Location: Missouri - USA
Posts: 119
A good example of this and real life application is to look a t a simple Buck Converter. The inductor in the buck circuit receives and "sends" it's current in the same direction.
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Magnetic Field Collapse Method
