Coil Current Direction when Power is Interrupted (2)

Here is an even more definitive test showing that coil current direction does NOT reverse when power is interrupted.

Please watch in the highest resolution available so as not to miss the short flashes. The “simple” version using just one LED is here:

Special thanks to commenter Gianni Laschi who suggested that I try two antiparallel LEDs in this test.

The input voltage is reduced to 1.8 volts, which is below the Vfwd of the LEDs so that the Green one, forward-biased when power is ON, does not light up or fail. The 1.8 volts supplied by the power supply is not enough to light the LEDs. When power to the coil is interrupted, only the Blue LED flashes, because the Current through the coil continues in the same direction as it was going while power was supplied, and the voltage rises until the Vfwd of the Blue LED is overcome. The Green LED does not flash at all, because when power is interrupted it is now reverse-biased — since the “bottom” of the coil is now a Positive terminal in analogy to a battery. See the schematic diagram at the beginning and end of this video.

TLDR: the fact that the Blue LED flashes, indicates that the current continues in the same direction through the coil as was flowing when powered. The fact that the Green LED does _not_ flash indicates that there is no reversed current hiding in there somewhere.

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