From: "Tesla list" <tesla@xxxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: Re: Terry filter construction
Date: Tue, 11 Oct 2005 16:24:47 -0600
Original poster: "D.C. Cox" <resonance@xxxxxxxxxx>
Air spacing is not relevant. Surface tracking is your main
consideration which usually exceeds the air values by 700-800%. We
make our polyethylene boards approx 2 inches wider than the NST we
are using with each HV side down the side and approx 1/4 inch
inboard. The center line contains the ground wire. This works out
to approx 7.5 to 8 inch wide PE board for a 30 or 60 mA NST. Don't
use PVC --- tracks too easy -- slightly surface hygroscopic.
Dr. Resonance
Hi Dirk,
At 11:52 PM 10/10/2005, you wrote:
I am now building my Terry filter but I have a couple questions.
How much distance must be between separate the parts of different
potential? For example, how much distance is required to prevent
it arcing over the circuit?
I have kept two things in mind while building these components.
1. Electricity follows path of least resistance.
2. Any distance smaller than safety gap will arc there
first. Approximately, how wide should the safety gap be set?
See the post Gerry just had:
""With the TC primary disconnected from the NST output, set the
safety gap spacing to "just not fire" with the NSTs maximum input
voltage (ie, 120Vac if plugged directly into the power outlet or
140Vac if using a step up variac). Once set, avoid the temptation
to widen the safety gap in order to get longer sparks. During TC
operation, you can widen the main gap until the safety fires
occasionally (for static gaps).
Gerry R""
Here is a chart of spark gap distances vs. voltage:
http://hot-streamer.com/TeslaCoils/Misc/SGapVolt.jpg
The peak voltage on a 15kV NST is 15000 x SQRT(2) = 21000V. The
chart says 20000V can arc 1.75cm (3/4 inch) between sharp
points. But the filter is probably only seeing 1/2 that between
points in any places so 10kV gives about 3/8 inch. So maybe double
that to 0.75 inch. Try to avoid any really sharp edges since they
like to corona anyway.
I have posted an image of my Terry filter template. I drew it up
in AutoCad, then printed it up. This makes drilling the holes a
lot easier and nicer. Do you see any errors in my template design?
<http://www.dirkstubbs.net/terry_filter_template.jpg>http://www.dirkstubbs.net/terry_filter_template.jpg
Looks fine to me.
Cheers,
Terry
Thanks
Dirk