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Chokes too close to primary?
From: Gary Lau 16-Sep-1997 0936[SMTP:lau-at-hdecad.ENET.dec-dot-com]
Sent: Tuesday, September 16, 1997 8:46 AM
To: tesla-at-pupman-dot-com
Cc: lau-at-hdecad.ENET.dec-dot-com
Subject: Chokes too close to primary?
Dear Dr. Resonance,
Your recent post reminds me of the unresolved tank-to-gnd arcing problem
I'm facing and posted several weeks ago. Summarizing, since installing
a pair of 9mH (30AWG x 2.38"D x 6.75"L air core) chokes, my tank circuit
wants to arc to any grounded point 3" or less away. Initially the chokes
were vertically mounted, top end about 5" below my primary. I also
suspected that the primary could be exciting the chokes (like little
secondaries) so I moved the xfmr(15K/30mA), bypass caps (600pF), chokes,
and series R's (3K/50W & damn hot!), 3-4 ft below the primary, orienting
the chokes horizontally, off axis from primary, and 90 deg from each
other. No Joy.
I had concluded that having a really effective pair of chokes has
essentially completely decoupled my tank from the ground reference and
that voltages like I'm seeing are all a part of the tank's resonant rise.
My solution has been to simply move things around to keep grounded points
away from the tank!
Back to the theory that the primary is coupling into the chokes, do you
really think that they need to be 10-15' distant to avoid coupling?
Yikes! If so, maybe this is a good reason to consider (well insulated!)
ferrite torroid chokes, they being less inclined to couple than solenoids?
How close can you bring a grounded surface to your tank before it arcs?
Regards, Gary Lau
Waltham, MA
>From: DR.RESONANCE[SMTP:DR.RESONANCE-at-next-wave-dot-net]
>Sent: Monday, September 15, 1997 7:29 PM
>To: Tesla List
>Subject: Re: New Testing
>
>To: Ed
>
>Another possible consideration --- are your high freq RF filter chokes
>mounted under your primary coil (or within a few feet)? If so they will
>pick up a high potential RF signal that could blow some components. We
>also learned this lesson the hard way many years ago. Now we mount all of
>our "filter" components in a separate HV power supply box that is usually
>10-15 feet away from the oscillator base itself.
>
>DR.RESONANCE-at-next-wave-dot-net
>
> From: Esondrmn-at-aol-dot-com[SMTP:Esondrmn-at-aol-dot-com]
> Sent: Monday, September 15, 1997 12:36 PM
> To: tesla-at-pupman-dot-com
> Subject: Re: New Testing
>
> In a message dated 97-09-13 09:03:10 EDT, you write:
>
> << Ed,
>
> If the rotary is firing only erratically, this isn't a symptom of
> improper primary tuning. If the protection gap across the cap is firing
> at a 1" setting, you have a significant problem with gap firing. Until
> you identify the problem, you may want to reduce your safety gap setting
> a bit, since breakdown of a 1" gap represents considerably more than 25
> KV AC. The combination of the rotary and the static gaps is apparently
> resulting on too high an effective breakdown voltage. In effect, you're
> "missing" more presentations than "hitting". Because of the high speed
> air-flow around the rotary electrodes, a rotary gap's breakdown voltage
> will be significantly higher than for an equivalent static gap.
>
> Now that you've tightenned up the gap spacing on your rotary, also try
> temporarily removing the series gaps and run only off the rotary, and
> try running at a mechanical breakrate of at least 360 - 480 BPS so that
> you get at least 3 - 4 presentations per half cycle. By reducing the gap
> spacing, you should arrive at a point where your system runs smoothly
> without the safety gaps firing. You can then gradually increase the
> setting via the series gaps until you're just below the point where
> erratic firing (or safety gap firing) begins. Depending on ballast
> settings (particularly with no damping resistors across your welder) you
> can get really horrendous transient conditions (4 - 6X the incoming 14.4
> KV) which won't take out your pig, but can take out your cap.
>
> See if this helps at all, and the best of luck to you Ed!
>
> - Bert H. --
>
> >>
> Bert,
>
> I now have the static gaps out of the circuit. Thanks for the tip, I
will
> reduce the safety gap across the cap to maybe .50 to .75". All I need
now is
> some decent weather.
>
> Ed Sonderman