Questions for Bob with no images attached

[eldarion]

Thanks for the help!  I will try to use the terms LMD and LEM properly next time.

Another one of the IGBTs was apparently on the fritz; it decided to blow just a little while ago.  This seems strange, as I am not stressing the bricks by any means (13.8V @ 6A maximum)!  I guess they may have been damaged in their prior life.  So far, both bricks have failed short-circuit.

This might explain my problems; a dying brick could cause the waveforms to be distorted enough to kill the effect, I suppose.  I hope that is all it is, and that replacing the bad brick will restore the odd effects I was seeing earlier.

The first replacement brick has already been sent out; I am trying to decide if I should complain about this one that just blew or not.

Eldarion

[Grumpy]

you might try putting a cup of water nearby to see if the field has any effect on it. When you get the field rotating properly, the water might respond to it.

Thought I was the only one that tried this sort of thing...

[Jdo300]

you might try putting a cup of water nearby to see if the field has any effect on it. When you get the field rotating properly, the water might respond to it.

Thought I was the only one that tried this sort of thing...

Nope  . I know this works. Moab and I played around with this when he was testing his TPUs and at one point, he was able to make standing waves in a cup of water that was sitting in the middle of his ring . It was pretty cool.

I hear from the MAGVID group that adding a little salt to it enhances the effect too.

God Bless,
Jason O

[eldarion]

Jason, Grumpy,

If we get odd things happening in a cup of water, I would be seriously concerned about the health risks of this system.  After all, we humans are mostly water...

All, especially Bob,

The replacement IGBT finally came, and I was also able to borrow a good 150MHz digital storage oscilloscope through the beginning of December.  This should help us nail down the problem with my controller, I hope!

I put a scope shot up on one of my websites here:
http://www.falconir.com/pics/DSC02278.JPG

The bottom trace (channel 1) is the "gate" (IGBT base) drive signal, and the top trace (channel 2) is the switched end of the primary coil.  This is F1, the highest frequency, set to a 500ns pulse width.  Just look at all that awful ringing!   I am pretty sure this is why nothing is happening--the field has major errors in it!  Every time the potential drops to near zero on the ringing sine wave, the rotation of the electric field gets messed up.  The magnetic field is probably also messed up, as the ringing will cause a small oscillating magnetic field to be generated in the primary.

Hmmm...now to get rid of it.  Fast, high-power snubber diodes?  Maybe Schottky?
EDIT: This is how I will do it: http://www.falconir.com/pics/snubber.JPG
I have some high-voltage silicon carbide Schottky diodes coming in the mail for testing--if possible, I will see if I can use a cheaper standard Schottky diode instead.

Eldarion

[Earl]

this is a carbon copy with no photos of my reply at:
http://www.overunity.com/index.php?topic=2872.msg56117#msg56117

Eldarion,

ringing is usually caused by
leakage inductance
leads too long
current loops too long

a toroid usually has low leakage inductance.

most people have trouble understanding that a circuit operating at 67 kHz, still needs to be built as if it was operating at hundreds of MHz, even 1 GHz, if there are pulses with fast rise and fall times.  Circuits with fast edge transistions MUST USE VERY SHORT LEAD LENGTHS.  By short, I mean ZERO mm.  Since zero mm is not possible, do every thing in your power to approach zero as close as you can.  Spare no effort.

Notice that your gate voltage has ringing that even goes negative.

Remember my image of current loops.  Look at this image again and ask yourself if all 3 of your currents loops have a length close to zero?
Is the distance between the ground of the driver IC and the IGBT source = to zero?

Don't forget E = L * di/dt and since we want di/dt to approach infinity to have RE effects, L must approach zero.
Even nanoHenries of inductance can cause sufficient and undesired voltage bounces.
Why do you think PCB designs use maybe a dozen SMD ceramic caps around each microprocessor?  The multilayer PCB has one layer dedicated only to being a ground plane.
These caps and CPU ground are connected to through-holes directly to the ground plane.

Post some photos in your thread of your physical layout, and I can make some more comments.

Would like to see a scope photo full screen of just the area in the attached photo.

Regards, Earl