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Re: Peak cap voltage, was 12kV, 30ma TC specs, 42" spark
From: Bert Hickman[SMTP:bert.hickman-at-aquila-dot-com]
Reply To: bert.hickman-at-aquila-dot-com
Sent: Tuesday, September 09, 1997 11:44 PM
To: Tesla List
Subject: Re: Peak cap voltage, was 12kV, 30ma TC specs, 42" spark
Tesla List wrote:
>
> From: FutureT-at-aol-dot-com[SMTP:FutureT-at-aol-dot-com]
> Sent: Tuesday, September 09, 1997 3:36 AM
> To: tesla-at-pupman-dot-com
> Subject: Peak cap voltage, was 12kV, 30ma TC specs, 42" spark
>
> Malcolm, All,
>
> I finally measured my peak cap voltage on this TC, sort of. I was
> concerned about scope grounding with the neon tranny midpoint
> grounded set-up, so I installed a potential transformer instead,
> which allows for grounding one side of the tranny to the scope.
> In previous experiments, I have found that by using the proper
> amount of inductive ballast, I can closely mimic the operation
> of the 12kV, 30ma set-up. For 42" sparks, the neon tranny
> draws 720 watts, and the potential tranny draws 680 watts, as
> measured using a Weston analog wattmeter, sync-gap phase
> was left unchanged for the two transformers. I attribute the
> greater power draw of the neon tranny to the greater losses that
> occur in such a tranny. Anyhow, the scope showed 32kV peak
> cap voltage. The gap was firing slightly late, so I should have
> re-adjusted the sync-gap phase, but I didn't. The formula shows
> that the caps should be drawing 430 watts, so the 680 watt actual
> wallplug draw doesn't seem too bad. And who knows how
> incorrectly the wattmeter may be reading. Gotta build the Dave
> Sharpe Opto-wattmeter! The potential transformer is rated at 1.5kVA,
> 14.4kV, but I turn up the voltage on the 12kV neon a little higher (than
> 120V in), so actual voltages are probably about the same.
>
> Regards,
>
> John Freau
John, Malcolm & all,
Nice experiment, John! Even though you're firing synchronously every
half cycle, you're still seeing the impact of resonant rise. This
experimentally confirms an earlier question regarding whether you'd get
resonant rise if you synchronously fired on each AC half-cycle.
Under these conditions, Glasoe ("Pulse Generators") predicts voltage
rise of Pi/2 times input voltage. Peak input voltage is about 20.4 kV
from your potential transformer, leading to a predicted peak of 31.2 kV
versus 32 kV measured - pretty close agreement! If you "missfire" just
once, or only fire synchronously 1/cycle, the predicted value climbs to
Pi*20.4 or about 64 kV (:^()! And it potentially (NPI) gets much worse
with asynchronous firing!
While your potential transformer will shrug off this transient, a neon
would probably be toast! This definately confirms the moral of not
running a neon with an async gap, especially if close to 60 Hz
resonance. However, it also speaks to the issue of conservatively rating
your tank cap!!
-- Bert --