I tried early 20-25 years go with a standard 50-400 Hz CT (1000:1) in an
oil container feeding a burden resistor a fast diode bridge, cap and
divider network (crude peak detector). It did sorta work and if you
calculate isec = Ipri * k was within 10% measured compared to predicted. A
peak detector is much closer to reality then a rms one energy transfers
etc. actually surprised it worked as well as it did, and everything is
COTS and relatively cheap.
Best Regards
Dave v<bert@xxxxxxxxxxxxxxxxxxxxx> wrote:
> Hehe... it's pretty erratic, especially when running at full tilt.
>
> I needed to extend the scope time base interval so that a complete
> "bang" event occurred during each sweep. At shorter sweep intervals,
> you'll get multiple ring-up and ring-down cycles which can be confusing.
> With this setting, I could see perhaps 3-4 cycles as energy transferred
> back and forth, with decreasing amplitude (P --> S --> P --> S --> P -->
> S) until the spark gap quenched. You can also try adding a breakout
> point and nearby ground gap at the top of the secondary to discharge
> secondary energy once it has nearly reached its peak voltage to reduce
> the number of energy transfers/bang.
>
> Bert
>
> Daniel Kunkel wrote:
> > Nice! Did you find that the current was very erratic or was it stable?
> >
> > On Wed, Jun 26, 2019 at 1:00 PM Bert Hickman <bert@xxxxxxxxxxxxxxxxxxxxx
> >
> > wrote:
> >
> >> Hi Dan,
> >>
> >> That may be why the ammeter burned out... :)
> >>
> >> I didn't have a scope and wideband CT when I had the 6" coil. In fact, I
> >> didn't even know that wideband CT's even existed until years later... :)
> >>
> >> I did measure peak secondary base current with a Pearson wideband CT and
> >> Tek scope on a 10" coil a few years later. Base current pretty much
> >> matched theoretically-predicted current. This was long before the
> >> excellent simulation models and tools we have today. Then, all we had
> >> was basic TC theory, Conservation of Energy, and Excel spreadsheets.
> >> Comparing primary bang size versus secondary peak current, and then
> >> back-figuring peak secondary energy, I found that about 85% of the
> >> primary bang energy made it to the secondary during by the peak of the
> >> first ring-up when P:S coupling (k) was about 0.2. So in that sense,
> >> agreement was pretty good.
> >>
> >> Bert
> >>
> >> Daniel Kunkel wrote:
> >>> Thanks for the info Bert. Did you find that your actual base current
> was
> >>> close to the predicted current (5a seems kinda low based on the numbers
> >>> from JavaTC on some medium sized spark gap coils).
> >>>
> >>> On Tue, Jun 25, 2019 at 1:37 PM Bert Hickman <
> bert@xxxxxxxxxxxxxxxxxxxxx
> >>>
> >>> wrote:
> >>>
> >>>> Hi Dan,
> >>>>
> >>>> Many years ago, I tried using an older thermocouple type RF ammeter
> >>>> (that I got at a hamfest) in series with the secondary base ground
> >>>> circuit in a 6" coil. As I recall, it was a 0-5A unit. It worked quite
> >>>> well at lower power levels, but I accidentally burned it out when
> trying
> >>>> to run it at slightly higher power levels. The resistance/heating
> >>>> element in the meter apparently was a bit fragile, particularly when
> >>>> trying to handle the high-current peaks from a spark-gap TC. YMMV...
> >>>>
> >>>> I had much better success using a wideband current transformer and
> >>>> oscilloscope.
> >>>>
> >>>> Bert
> >>>>
> >>>> Daniel Kunkel wrote:
> >>>>> Hello list,
> >>>>> I have been thinking about using a current meter to monitor the base
> >>>>> current of the secondary coil, mainly as a tuning aid. It appears
> there
> >>>> are
> >>>>> HAM radio guys that use RF ammeters, and there are even plans to
> build
> >>>> your
> >>>>> own, however, I wonder how accurate it would be (due to dirty EMI and
> >>>>> irregular current draw)? Has anyone tried this? Or is there a better
> >> way
> >>>> to
> >>>>> ensure the tune is spot on other than observing for best streamer
> >>>>> production?
> >>>>> Thanks,
> >>>>> ~Dan
> >>>>> Kansas City area...where the ground might be starting to dry out, but
> >>>> only
> >>>>> a little bit
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> >>>>>
> >>>>
> >>>>
> >>>>
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> >>
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>
> --
> Bert Hickman
> Stoneridge Engineering LLC
> Woodridge, Illinois, USA
> http://www.capturedlightning.com
> +1 630-964-2699
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