Eldarion and Bruce's build of Bob's Energy Converter

[eldarion]

Hi Grumpy,

No, I am driving the primaries closed-ended, as Bob does.  The IGBTs are in a pull-down configuration, so they are supposed to generate negative pulses, but the ringing is just so bad that the primary waveforms look nothing like they should.

Damping the ringing just plain doesn't work.  As soon as one of the other primary coils pulses, it sets up ringing of a different frequency in the non-driven primaries.  Seems that the only way to get rid of the ringing completely would be to tie the switched end of the coil to +13.8V, which is the equivalent of shorting out the coil.

If I physically disconnect two of the primaries, and drive only one, I can get the waveform to look pretty much perfect.  As soon as I connect even one of the other primaries, however, everything breaks loose and I get the waveforms that I posted above.

I also do not like how long the pulse actually is at the primary coils.  When the switched primary end is released, it is taking an awfully long time to return to +13.8V...

Eldarion

[Grumpy]

Sounds like the primaries are in radiating tranversely - conventionally - and you need then radiating longitudinally.  I think Bob mentioned this very early on.  Mark Snoswell explored this to a great extent.  Very interesting results.

See, you have both types of wave going on and you can favor one or the other.  They can even be separated, the longitudinal and transverse components that is.

Short fix: narrower pulses.  Passive differentiation with C and R.  Hell, double differentiate it.  Pulse will get shorter and amplitude may go down to some degree - at least on an oscope - the spectrum will likely get very active as all the harmonics start showing up.

Small R and Small C - like a few ohms and a few pF
http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/experiment/diff/diff.html

EDIT:  also might try choking the inputs to the primaries.  Potential required, not current.

[eldarion]

Hi Grumpy,

Thanks for clearing that up!  I had, early on, been confused by all the discussion about longitudinal resonance--longitudinal radiation makes a whole lot more sense.  Primary resonance does not seem to be something that we want!

I will try double-differentiating the output of the MOSFET drivers themselves, with no IGBTs in between, and see if something interesting happens.  And yes, the HV potential will be connected.

The only thing I could see as a problem is that there will be two pulses for every input pulse--one positive pulse on the low-to-high transition, and one negative pulse on the high-to-low transition.  Wouldn't this be a bad thing?  I wonder if a sawtooth input to the differentiator would work better.

I can't test right now, as I am away from my bench, but for sure I will post some results, positive or negative, later on tonight.

Eldarion

[Grumpy]

Get rid of it with a diode, which is not perfect, after the differentiator.  You will have to have enough current to drive the diode at the diode.

You do not want undershoot (overshoot in your case since pulse in negative).

http://www.ortec-online.com/electronics/amp/03_4.htm

adds a pot across the cap - can also use a fixed resistor

[eldarion]

OK, thanks!  Everything seems OK to me now, we'll see how it does on the bench!

Eldarion