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RE: Capacitor Help
Original poster: "Lau, Gary" <Gary.Lau@xxxxxx>
Yes, at first glance it's not clear what is accomplished by wiring a
safety gap in parallel with the main gap. There's a couple of reasons.
This doesn't apply to you since you're using a static gap, but when
using a rotary gap, the safety gap kicks in should there be a fault with
the RSG mechanics.
For static gap users, it's all too easy to open the gap up just a bit
more (accidentally or on purpose), and this is where you get into
trouble. Having an independent safety gap that is set properly provides
a measure of fool-proof protection, although having the self-discipline
to set it properly and leave it there is uncommon!
The topic of RF grounds and green-wire grounds confuses many beginners
and stirs up controversy among seasoned coilers. You could spend a week
searching the Pupman archives and still come out confused!
First, unless your coil is low powered (and there is no clear definition
here), the secondary base should go to an "RF ground", separate from the
green-wire mains ground. The RF ground is the return path for the high
frequency streamer current, and you don't want that going through your
mains wiring!
When we use a 3-terminal safety gap, the middle terminal goes to RF
ground. Consider what happens should a streamer strike your primary
(instead of your strike rail). The entire primary is raised to a very
high voltage. If there is a middle terminal at RF ground, the suddenly
"hot" primary will arc to the middle terminal, and the discharge current
will go harmlessly into the RF ground. If you did not have a middle
terminal, the only path for the streamer current to follow is through
your NST into your mains wiring.
So the RF ground should be an independent connection to something that
is at least capacitively in close proximity to the earth. This can be a
ground rod, or a large sheet of metal on the floor, or a rail road
track, or a chicken wire structure or...
Regards, Gary Lau
MA, USA
> Original poster: "MalcolmTesla" <tesla@xxxxxxxxxxxxx>
>
> ----- Original Message -----
> From: "Tesla list" <tesla@xxxxxxxxxx>
> To: <tesla@xxxxxxxxxx>
> Sent: Friday, December 16, 2005 12:58 PM
>
>
> > Original poster: "Lau, Gary" <Gary.Lau@xxxxxx>
> >
> > Hi Malcolm:
> >
> > VERY nice looking primary construction!
> >
> > Regarding a safety gap across your MMC - don't. Should a gap
across the
> > MMC fire, the discharge current is limited only by the impedance of
the
> > gap arc, which is very low, and over-current damage to the MMC may
occur
> > if it happens too often. Instead, the safety gap should be in
parallel
> > with the main gap.
>
> Rich said the same thing. Put the safety gap across the NST which is
> parallel to the spark gap. I'm not sure I understand how that helps.
Rich
> mentioned a third terminal in the safety gap which goes to ground. I
assume
> 110 green wire ground?
>
> > The same safety gap in parallel with the main gap will limit the
voltage
> > seen by the MMC to the same level, but should that fire, the
discharge
> > current will be limited by the primary coil's impedance - the same
as
> > during a normal gap discharge. The same level of protection is
> > achieved, without risk of cap damage.
>
> How does the safety gap drop the excess voltage across the caps any
better
> than the spark gap is already doing when the spark and safety gaps are
in
> parallel?
>
> Thanks
> Malcolm
>
>
> > Regards, Gary Lau
> > MA, USA
> >
> >
> > > Original poster: "MalcolmTesla" <tesla@xxxxxxxxxxxxx>
> > >
> > > ----- Original Message -----
> > > From: "Tesla list" <tesla@xxxxxxxxxx>
> > > To: <tesla@xxxxxxxxxx>
> > > Sent: Thursday, December 15, 2005 7:58 PM
> > >
> > > Thanks. I got the strike ring make tonight too
> > > http://www.v8-ranger.com/temp/tesla/19.jpg
> > > I wasn't sure if I was supposed to connect one end of it to
earth or
> > not?
> > >
> > > And I made my capacitor bank or MMC as I believe it's called. I
also
> > put 10
> > > Meg 1/2 watt resistors across each cap as suggested.
> > > http://www.v8-ranger.com/temp/tesla/20.jpg
> > > http://www.v8-ranger.com/temp/tesla/21.jpg
> > >
> > > Still need to make the safety gap across the MMC and wire up the
HV
> > stuff.
> > > Oh and winding the secondary and building my torid are the last
two
> > major
> > > things.
> > >
> > > Do I adjust the safety gap across the MMC slightly larger than
what
> > ever my
> > > spark gap gets set at? 1/8" or 1/4" wider, maybe?
> > >
> > > Thanks
> > > Malcolm - KC
> > >
> >
> >
> >
>