[TCML] More on my SISG coil
mustang3 at cox.net
Wed Sep 10 09:09:21 MDT 2008
> On Tue, Sep 9, 2008 at 6:59 PM, miles waldron
> <mileswaldron at comcast.net>wrote:
> > These comments are in response to Gary Lau, who writes on this
> > Gary is a very nice person. The following opinions are mine, and for
> > record I agree completely with everything Gary has said. Someone
> > me know if I have missed the point entirely, and if that is the case
> > am sorry.
> > Terry filter protection for a pole pig is pointless. A pole pig is
> > to be struck by lightning over and over again during its lifetime.
> > ever been hit by lightning? As equipment goes, a pig is typically
> > avoid transformer limitations. You can do just about whatever you
> > a pole pig, and it will still be there (not hindered in any way)
> > explosion.
> > Miles Waldron
> > -----Original Message-----
> > From: tesla-bounces at pupman.com [mailto:tesla-bounces at pupman.com] On
> > Of Lau, Gary
> > Sent: Tuesday, September 09, 2008 6:25 PM
> > To: 'Tesla Coil Mailing List'
> > Subject: RE: [TCML] pole pig protection
> > Opinions vary on this topic. Here is mine.
> > First off, in contrast to NST's and MOT's, pole pigs are extremely
> > and well designed. They are designed to be undamaged by lightening
> > strikes.
> > While it is not unheard-of, damage to pole pigs is a very rare
> > As to protecting the pig from RF - I assume that your TC circuit has
> > main gap in parallel with the pig HV secondary. Please consider
> > ONLY time there is RF oscillating in the TC primary or secondary,
> > gap is conducting. If the spark gap is conducting, it is
> > shorting out the pig's HV secondary, so there's not a lot of RF to
> > against.
> > Now, it's not entirely true that the gap is conducting continuously
> > each bang. Each time the current through the gap passes through
> > the
> > resonant frequency, the gap arc extinguishes briefly for a few(?)
> > nanoseconds. During this brief time the primary rings with its
> > self-capacitance, in the tens of MHz region. The initial magnitude
> > oscillation is Vbang, and since it is in series with the tank cap,
> > initially at Vbang, the combination of the two in series (what the
> > winding sees) is 2Vbang. This, IMHO, is the thing that needs to be
> > filtered, at least for NST's and less sturdy transformers. And this
> > easily and effectively attenuated by the R-C filter in the Terry
The really neat thing about the SISG coils is the high voltage
requirement. 1 MOT with a voltage doubler (standard microwave PS) will
work with 4 sisg modules. Each module fires at 900 volts. 1 board has 4
modules; fires at 3600 volts. The 1st PS that the coil was running with
was 3 MOT's, secondarys in series with a current limiting choke in the
primarys. I used PFC caps to reduce the current draw from the wall. With
this PS, I use 12 sisg modules (10.8KV). With the pole xmfr, I'm using
16 modules. The cap I use is 133Nf at 30KV.
The other cool/odd thing about a SISG coil is the variac on the PS.
You tune it by setting the input voltage until it fires smooth. Too high
and the firing is chaotic. Too low and it doesn't fire at 120 HZ; which
makes for a smooth buzz. James
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