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Re: [TCML] SRSG "sputter"
Hi Joe,
I didn't understand the before and after circuit configurations of your
phase Variac. A Variac is a 3-terminal device - Call the two ends of the
inductor A (hot) and C (neutral), and call the variable tap B. Mains ground
only goes to the case for safety (and should be used). In the phase shift
circuit, we want just a 2-terminal variable inductor, so use terminals A & B
or B & C (plus the case ground).
If I understand your post, you previously used "the hot lead from the input
to the variac and the hot lead from the output". Terminals A & B.
You then switched to "the hot and neutral from the output circuit".
Terminals B & C?
Both configurations should go from 0-100% of the total inductance, the only
difference being that in one the full inductance is at the CW end and the
other is at the CCW end. I don't think there should have been any
difference in total phase shift achievable, if I understood the
configurations correctly.
You mentioned seeing phase shifts of 15 and 25 degrees. Since 360 degrees
is 16.67 msec, 15 degrees is only 0.69 msec, and 25 degrees is 1.16 msec. Is
this correct? It would be good to verify that the motor shaft varies by the
same amount.
Regards, Gary Lau
MA, USA
On Sun, Jul 11, 2010 at 1:54 AM, Joe Mastroianni <joe@xxxxxxxxxxxxxx> wrote:
> HI Gary and John,
> I have made some mods to the phase control variac. Previously, what I had
> been doing is using the hot lead from the input to the variac and the hot
> lead from the output (ignoring the neutral and ground) and using that as the
> variable inductor.
>
> I put the phase shift circuit onto the oscilloscope channel B along with
> wall current channel A and looked at what happened when I rotated the
> variac. I got a phase shift along with a distortion of the waveform from a
> sinusoid to a distorted triangular shape, the peak of which maxed at about
> 15 degrees away from the top of the public service voltage before increases
> in inductance caused more voltage drop than phase shift. After about 15
> degrees I was down to about 60V and the motor lost lock. This didn't seem
> too out of whack with what I had been told - that I'd only get about 15
> degrees.
>
> Then I tried just using the hot and neutral from the output circuit only as
> in the picture on this page (http://www.hvtesla.com/phase.html) and I'm
> noticing about 25-30 degrees deflection before the motor loses lock. Thanks
> to Brandon for the help on that one.
>
> Now, as it turns out I have been out of the house all day on a family
> excursion, and only returned home this evening to do the experiments. It's
> a bit late to run the coil as it would indeed wake the neighbors, so I am
> going to have to wait till tomorrow AM to run some experiments watching the
> streamers. I did try to get a video using my iPhone yesterday in the
> semi-darkness, but the dark image response of that thing is pretty awful -
> even the streamers are hard to see in what it thinks is pitch black. I need
> to get a real camera.
>
> More to come.
>
> With regards,
> Joe
>
>
> On Jul 10, 2010, at 3:08 PM, Gary Lau wrote:
>
> > Hi Joe,
> >
> > There's no way that having the gap BPS being a sub-multiple of the
> resonant
> > frequency would affect anything. When the SRSG phase is significantly
> out
> > of whack, the gap fails to fire at the end of a mains half-cycle because
> the
> > electrodes aren't aligned at the voltage peak. So the voltage now begins
> to
> > charge in the opposite direction. But contrary to intuition, this energy
> > isn't simply "lost". In an L-C resonant circuit, the energy transfers
> > alternately between voltage in the cap and current in the inductor. The
> L-C
> > circuit at this point is the cap, and the NST secondary winding,
> resonating
> > at or near 60Hz. Yes, you have a Larger Than Resonant sized cap, but
> when
> > NST secondary currents flow through capacitive loads, we think that the
> > current limiting shunts saturate, and ferroresonance kicks in and strange
> > stuff happens, permitting at or near mains resonance. Bottom line, the
> > energy isn't lost, but when the voltage reverses, then charges to the
> > opposite polarity, it will reach a FAR higher voltage than on the
> previous
> > half-cycle, enough to break down a safety gap or insufficient RSG
> > insulation.
> >
> > As John said, it's not possible that the cap can carry a charge between
> > bangs. Once a spark gap fires, it won't stop firing until pretty much
> all
> > of the energy has been dissipated. This happens pretty fast, and the
> fact
> > that the electrodes are spinning quickly doesn't matter.
> >
> > Now that your gap timing is in the ballpark, can you describe what
> happens
> > as you sweep the phase adjustment Variac through its range?
> >
> > Regards, Gary Lau
> > MA, USA
> >
> > On Sat, Jul 10, 2010 at 12:09 AM, Joe Mastroianni <joe@xxxxxxxxxxxxxx
> >wrote:
> >
> >> Hi All,
> >> Well, indeed the problem was curable by advancing the timing on the
> rotor
> >> about 30 degrees. Now I can bring it up to full power - BUT - I would
> say
> >> that on full power the arcs aren't as large as they were when I had the
> >> "sputter" problem. After doing a bit of reading I've come to the
> conclusion
> >> that the sputter was indeed some off-timing resonance issue where I was
> not
> >> entirely discharging my MMC bank. Perhaps it was some out-of-control
> >> ringup issue that the safeties were saving me from, with the pulses
> hitting
> >> the cap bank at some multiple of the resonant frequency. I measured my
> >> Thus the safeties were firing to offload the additional charge.
> >>
> >> Java TC suggests my resonant freq is around 130khz but it wouldn't
> surprise
> >> me if it was closer to 120khz, which, perhaps, would cause some issues
> at
> >> 120bps under certain conditions. It would take me going out and getting
> >> some HV probes for my scope to see it for myself...
> >>
> >> Meanwhile, it works now fine.
> >>
> >> Of course, this will not stop me from trying the other SRSG designs.
> I'm
> >> too curious.
> >> I'm also going to try an ARSG, as I do like the sound.... ;-)
> >>
> >> Joe
> >>
> >>
> >>
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>
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