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Author Topic: Induction coil - let's clear this up  (Read 2631 times)

Offline nix85

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Induction coil - let's clear this up
« on: January 16, 2020, 05:00:25 PM »
In first video below they say as primary field collapses, it induces backward current in the primary, flowing against the battery current.

Yet in the second video we can clearly see that after primary is turned off, there is no current through it and it has voltage spike around 50V in same direction as battery voltage, NOT in reverse direction.

https://www.youtube.com/watch?v=lWyn_eV-DzM

https://youtu.be/xXteh1Ch738?t=834

Seems first video is wrong, what you think.

Offline nix85

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Re: Induction coil - let's clear this up
« Reply #1 on: January 16, 2020, 06:24:19 PM »
We all know inductor will try to maintain the current in the same direction after supply is cut off. http://www.learnabout-electronics.org/ac_theory/dc_ccts44.php

Offline kajunbee

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Re: Induction coil - let's clear this up
« Reply #2 on: January 16, 2020, 08:39:06 PM »
If the current were in opposite direction then a flyback diode would be pointless. The polarity changes but current is driven in same direction. The inductor now acts as source instead of a impedance. At least that's the way I understand it.

Offline kajunbee

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Re: Induction coil - let's clear this up
« Reply #3 on: January 21, 2020, 05:25:03 PM »
I had not watch the video and did not realize the inductor was ignition coil. But I still believe he is showing current charging condenser in wrong direction. It appears to me that when field collapses it will charge condenser to higher voltage, but current will flow in same direction. The charge doesn't flow across the switch contacts, but instead by displacement current through condenser. Once it charges to this higher voltage it will then want to discharge. At this point is when current will flow opposite direction as shown in video. There will be a ringing oscillation setup with the series LC circuit. How does that sound to you?