Re: Reliable Moderate HV testing

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jonathan Peakall by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jpeakall-at-madlabs.info>

Antonio,

So that's it then, no way other than a spark gap eh? Some things don't
change, I guess. I'm going to try the charging a cap thing and see what I
get.

The main thing I am looking for is consistency. That way, even if I don't
know what the actual output is, I can at least get a handle on performance
Vs various changes. As it is right now, it can be hard to tell if the unit
is performing better or not...Judging output visually is tough.

What about current? Any easy way to measure that?

Thanks for your time,

Jonathan Peakall
> Tesla list wrote:
> >
> > Original poster: "Jonathan Peakall by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <jpeakall-at-madlabs.info>
>
> > I am having trouble measuring the output of my flyback system. The
> measurements
> > vary widely. I am using a 100:1 HV probe marked " X100 For 10mohm inputs
> model
> > 1MA-100-10" and a Metex M-4650CR DMM, rated to 200kHz. When I hold the
> probe, I
> > get much lower readings when measuring AC off the flyback. I understand
> that I
> > am capacitively coupled to the probe and grounding it, but which reading
is
> > "real" me hanging on to it or not? Which represents the "working"
voltage of
> > the system?
>
> None. The flyback generates short pulses, and a DC meter will only
> measure
> the average value. In AC mode you will see a scaled version of the
> average value of the rectified output. Even a true RMS meter will only
> show a low measurement. Conventional meters usually don't have a "peak
> value" mode, that is what you want.
>
> > Also, while hanging on to the probe, if I put the flyback output through
> a full
> > wave bridge, I get much less than 1/2 of what I read on the AC side.
>
> Probably the high voltage destroyed the diode bridge...
>
> > Further, when reading the AC output of the system, if I disconnect the
ground
> > lead, sparks will jump a good distance from the lead to the ground. This
> makes
> > me nervous. I tried using my mains ground, which should be isolated from
> the RF
> > ground of the system, and the same thing happens. What if I put a HV
probe on
> > the ground side? Is my DMM at serious risk?
>
> Certainly, YES. Keep the high-voltage system and the meter grounded
> while making measurements. Disconnect always the high voltage
> connections
> first (or better, turn everything off) before disconnecting the ground.
>
> > So what can I do to get at least consistent if not accurate readings?
>
> Use a spark gap to evaluate voltages by spark length. Or, rectify the
> output of the flyback with a high-voltage diode (if it hasn't already
> one),
> connect a high-voltage capacitor across the rectified output, and
> measure
> the DC voltage in the capacitor, that will be close to the peak output
> voltage, if the probe is not loading excessively. Probably you are
> already approximating this, using you as the ground plate of the
> capacitor.
>
> Antonio Carlos M. de Queiroz
>
>
>
>