BEMF current reversal.

[Allen Burgess]

Buck converter animation.

Great animation Dave45! It clearly shows that the current does NOT reverse during the discharge of the coil. THANKS for posting that. The scope shot posted earlier in this thread also clearly shows the current dropping to zero when the coil discharges. It does NOT show the current reversing. As has been explained many times on a lot of forums the voltage appears to change direction because during discharge the coil becomes the source and not the load. So the voltage changes polarity but the current continues to flow in the same direction until the coil is discharged.

The problem with this animation is that it depicts a solenoid coil wrapped around an air core. The Woopyjump coil under discussion has a laminated ferrite U core that's strongly influenced by spinning magnets. The ferrite U core retains a powerful magnetic flux field that's changing and requires the application of both Faraday's and Lenz's laws to determine the actual direction of BEMF current flow from the coil.

[Allen Burgess]

Woopyjump's video

Woopyjump's primary and hi-voltage seconday power coils both have ferrite U cores. Woopyjump demonstrates the nullification effect of disconnecting the capacitor. Question; What role does the capacitor really play in the circuit? Answer; Double reversing the primary's original reversed current BEMF so the primary and secondary power coil polarities match.

[Allen Burgess]

Current reversal.

@OrionLightShip,

John g demonstrates conclusively that the addition of ferrite cores, multiple windings and magnets reverses the direction of back spike current, so the use of "always" tends to be pedantic and misleading. There are legitimate exceptions to Cifta's hard and fast rule.

[OrionLightShip]

As has been explained many times on a lot of forums the voltage appears to change direction because during discharge the coil becomes the source and not the load. So the voltage changes polarity but the current continues to flow in the same direction until the coil is discharged.

Once again, your intelligence shines through!
This is a simple case of sign convention people don't get.
The conventional current flow (positive, so as to ignore those pesky electrons) flows in the same direction, as the coil switches from load to source as you mention above.

Richie Burnett also shows this to be the case in his description of dc resonant charging.

I think perhaps people get confused because they use mosfets that switch off and then use a diode to redirect the positive current back into the source battery. You can just as easily direct that positive current into the drain. That operation has nothing to do with the current flowing from a coil which is ALWAYS in the same direction.

[Dave45]

If we take an iron rod an place it on the end of a magnet the magnetic field is expanded to include the iron rod and the iron rod is also engulfed in the magnets eddy currents, when the two are separated the eddy currents collapse and if a coil is wound on the iron rod the eddy currents collapse into the coil windings.

Thats how a coil takes energy from a magnet, the magnet draws energy from the ambient to replenish itself.

[Dave45]

Yes voltage changing direction is also an indication that its the eddy currents that collapse when the magnetic field is turned off. Eddy currents create a magnetic field opposite the magnetic field that created them.

We can also see now how a coil passing a magnet steals energy from the magnet,

[citfta]

Great animation Dave45! It clearly shows that the current does NOT reverse during the discharge of the coil. THANKS for posting that. The scope shot posted earlier in this thread also clearly shows the current dropping to zero when the coil discharges. It does NOT show the current reversing. As has been explained many times on a lot of forums the voltage appears to change direction because during discharge the coil becomes the source and not the load. So the voltage changes polarity but the current continues to flow in the same direction until the coil is discharged.

[Dave45]

A study of the buck converter is eye opening, when the switch is off the current doesnt run to ground but cycles through the circuit, if it (current) was a product of the battery it would run straight to ground.

There is an animation on this page that illustrates the current flow in a buck converter. Buck Converters
This site also has a page on boost converters, cool site.

[Dave45]

I like the Leedskalin attachment by john_g and the rubber band analogy.

It is interesting, one can say we have a Positive and Negative voltage (referenced to ground) but we almost never say we have a Positive or Negative current.

Electron current is generally seen or accepted as going one way only, unidirectional, from Negative to Positive.

If neg electrons flow from neg to pos and current flows from pos to neg then current is a product of electron flow.

[Sputins]

Contra-flow?

I like the Leedskalin attachment by john_g and the rubber band analogy.

It is interesting, one can say we have a Positive and Negative voltage (referenced to ground) but we almost never say we have a Positive or Negative current.

Electron current is generally seen or accepted as going one way only, unidirectional, from Negative to Positive.

[Dave45]

https://youtu.be/0d6chzb7Z1c

What you are seeing in this vid is the eddy currents of a magnet being ionized using high voltage.

[Dave45]

Research eddy currents Hi-Techndt

[Dave45]

The magnetic field does not turn electric when it collapses, its eddy currents that create the spike.

[Dave45]

Hi All

Re the direction reversal, I wrote the attached a few years back, that may be of help. It depends upon the position of the voltmeter.

Kind regards

John

The spike is pos,
If the pos spike is ran into another coil its spike or collapse will be neg.
So what does this imply, the collapsing field is zero energy accumulated from the aether, opposites attract.
We create the magnetic field but the aether supply's the electric field or eddy currents if you will.

[Allen Burgess]

Woopyjump video

@John g,

Here they are; "Capturing energy from the Flyback Spike" 1 & 2:

1.- https://www.youtube.com/watch?v=tag5OlvPi54

2.- https://www.youtube.com/watch?v=y4S3XvloAnM