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[TCML] Terry filter - are banana plugs okay?
Hello,
Are banana plugs okay to connect the NST to the terry filter, and the
primary to the NST? I have seen several designs e.g.
http://hot-streamer.com/TeslaCoils/MyCoils/BigCoil/protection.jpg
using banana plugs. Are these strong enough? Specs usually indicate
relativelty low voltage
I'd like to be able to disconnect all components quickly, and banana
plugs look good in that respect.
However, this terry filter looks really good -very elegant.
http://ian.macky.net/tesla/nstfilt1.jpg
many thanks!
Thomas
-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf Of Lau, Gary
Sent: 07 April 2008 16:11
To: Tesla Coil Mailing List
Subject: RE: [TCML] Terry filter - does one need the current
limitingresistorswith a current limited NST?
One may indeed calculate the cutoff frequency of the R-C filter, but I
think the answer would surprise most folks. If R is 1K and C is 500pF,
the -3db frequency is 1/2pi*R*C or 318KHz. But most medium-large coils
run at a much lower frequency than that, so the attenuation would be
much less than 3db. Shouldn't we be shooting for a much lower cutoff
frequency to ensure a thorough attenuation?
No. Contrary to intuition, it's not the coil's resonant frequency that
the R-C filter is there to attenuate. Assuming that the spark gap is
across the NST, when the primary is ringing at its resonant frequency
Fr, the spark gap is ON, pretty much a short circuit, so the NST sees
very little in the way of Fr, even with no filter.
Pasting from my web page on this topic (please view the page if the
context of the excerpt below is unclear):
http://www.laushaus.com/tesla/protection.htm
"I believe the more significant NST hazard (aside from too-wide gaps) is
due to VHF voltage bursts generated during the gap conduction. These
bursts are twice the peak tank voltage and in the tens of MHz. As I
mentioned, gap conduction is not really continuous, but ceases briefly
each time the tank current crosses zero as it rings at its resonant
frequency. At the moment that tank current crosses zero and the gap
ceases conduction, the voltage across both the tank capacitor and the
primary coil are at maximum, or Vtank. The primary coil has some
parasitic self-capacitance, C-self, associated and in parallel with it,
and it is also charged up to V-tank. As soon as the gap opens, the
primary coil and its C-self ring at their own resonant frequency, about
24 MHz in the case of my primary. This ringing is in series with the
tank capacitor, sitting at Vtank, so the combination of the tank
capacitor and the ringing primary inductor in series now present a
voltage of 2Vtank across the non-conducting spark gap and to the NST if
no protection network exists! But 24 MHz is child's play for an R-C
network to filter out, and is easily attenuated."
Regards, Gary Lau
MA, USA
> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of miles waldron
> Sent: Sunday, April 06, 2008 11:19 PM
> To: 'Tesla Coil Mailing List'
> Subject: RE: [TCML] Terry filter - does one need the current limiting
resistorswith a
> current limited NST?
>
> So, do the R's in the terry filter along with the caps, make a low
pass
> filter? If this is true, then it should be easy to figure out what the
cut
> off noch is, or make a bode plot.
>
> Miles Waldron
> 678-557-7737
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