Lister Generator Systems - What Are My Options?

[Doug]

Ron, I'm baffled abot your success with a cap across the rectified harmonic output.  Both Bill Rogers and I have messed with that and had no change in the waveshape.  His is an ST12, mine is an ST3.


Diode noise is way too fast a phenomina to cause the dips in the waveform.  So something else is going on.  Also the "flat topping" of the waveform you mention  is not typical... o'scope screen shots by Bill R, Jeff M, and myself don't show that. So something is unusual about your ST5.  I know you're   highly competent and you got the results you did, but I wanted to let you know that it isn't consistent with other's work I also respect or my own. 

I hope Bill will comment but I don't know if he reads here anymore.

Edit-  Sorry Ron, after reviewing the screen shots of your o'scope, I see that you did have an unusual high frequency distortion caused by your harmonic, and your capacitance did do the trick on that, though the harmonic "hump" was still present.  The "flat topping" you see is also high frequency, and is a bit more than normal but still is typical ST peak distortion caused by the winding placement.  And of course you're right that some passive filtering of the output (LC) would reduce that greatly. Sorry about the confusion on my part.

Bruce M

Flat topping sounds like saturation, once you push above 100,000 lines per inch of flux the wave form starst to distort and this is typical of what it would look like.....
Reduce the excitation ( I know this will reduce the voltage ) and just look to see if it cleans up. If you get a sine wave back then that would confirm saturation. Next question is why?

[ronmar]

It wasn't so much a flat top as another frequency ringing across the peak of the sine wave.  I have to look back thru my pics, but I may have been at a higher than normal output voltage at that point and not reducing the excitation as much as I could to compensate for the increase the caps gave me.  I don't have a large variety of resistors of that capacity to combine so I was taking what was adequate to accomplish my testing.  Excitation might also explained why it wasn't consistent from cycle to cycle which would go along with excitation induced, if a particular harmonic winding was outputting a little greater when stroked by the rotating magnetic field.  It could also be that one diode set flows a little better than the other.

Ron 

[Doug]

Odd harmonics will make the kleading and trailing edge of the wave steeper as well as flatten the top.

Saturation will simply flatten the top....