What is that hump ?

[Verpies]

What causes that hump ?



The context is in this video.

Notice that the "yellow" scope probe forms a 1-turn loop around the transformer's core.  This is not a proper current probe.  It picks up dΦ/dt (it picks up the changes in the amount of flux that penetrates this loop).

In the beginning I thought it was the saturation of the core, but it does not add up.  The primary current might increase rapidly at saturation but not the magnetic flux in the core.
The falling edge of the hump could be caused by the approach to the V/R limit ...but why does it oscillate later slowly ?

[picowatt]

What causes that hump ?



The context is in this video.

Notice that the "yellow" scope probe forms a 1-turn loop around the transformer's core.  This is not a proper current probe.  It picks up dΦ/dt (it picks up the changes in the amount of flux that penetrates this loop).

In the beginning I thought it was the saturation of the core, but it does not add up.  The primary current might increase rapidly at saturation but not the magnetic flux in the core.
The falling edge of the hump could be caused by the approach to the V/R limit ...but why does it oscillate later slowly ?

Verpies,

When I see videos like this I just want to reach thru the screen and grab the scope controls.  When the vert sensitivity is turned down to 200mv with that much signal exceeding the vertical height, you just have to wonder what may be clipping in the front end...

Anyway, take a look at the 1:40 and 2:00 timestamps in the video.  You will see that without the magnet, the "hump" appears to start just prior to the falling edge of the green channel.  It looks to me that this is where the core is beginning to saturate and core leakage to the loosely coupled probe loop begins to increase.

At around 4:40 and onward, where he has placed the magnet and is rotating it, it appears he is causing the saturation point (as noted above) to occur earlier.  Once saturated (the peak of the "hump"), flux change decreases so the coupling to the scope probe loop decreases, creating the falling side of the "hump".  Moving the magnet around modifies the saturation point causing the "hump" to peak earlier and later but always prior to the green channel fall time.

The spike and ringing after the green channel fall time occurs with and without the magnet.

That would be my guess...

PW

ADDED:  I have no idea why after posting this it shows just below this line that Verpies last edited it....  Weird...

[Verpies]

The spike and ringing after the green channel fall time occurs with and without the magnet.

I agree about the ringing after the green channel fall time occurs.
I also agree with your prior analysis.

...but what about the slow ringing before the green channel fall time occurs (later in the video)?

ADDED:  I have no idea why after posting this it shows that Verpies last edited it....  Weird...

Because I edited your post to make the inline photo in my quote smaller. This way it takes up less space and scrolls faster....

[picowatt]

What slow ringing are you talking about?  Are you talking about the "hump" itself? 
The only ringing I see is after the green channel falling edge (turn off).

The one at 6:58.

[picowatt]

The one at 6:58.

Verpies,

I am guessing that once the core saturates, the unchanging core flux allows the shorted secondary to release some stored energy which bucks the core magnetization and desaturates the core a bit.  This allows the core flux to increase again, until the core saturates again.

The cycle repeats as a damped oscillation.

Again, just my guess...

PW

[picowatt]

Verpies,

What is going on with this thread?  Look at reply #3.  It says that was posted by me when it was actually you that posted.  The quoted text also has us backwards.

Again, weird...
PW

[Verpies]

A race condition.  I think I have it licked now.

[picowatt]

A race condition.  I think I have it licked now.

Verpies,

I'm too old to race...

Do you have an opinion regarding my response at reply#4?

PW

[Verpies]

I'm too old to race...

I meant this race condition.

Do you have an opinion regarding my response at reply#4?

I am still thinking about it.
Here is a rushed and not well though out one: The power supply is constantly pushing current into the winding when the green pulse is low. Eventually that current reaches the V/R limit and I see no mechanism for it to go down quickly except by some LC damped oscillation.  ...but that should be happening all the time if it's there.