Unfortunately, it's difficult to experiment with two cap values to see
which works better - you can't change just the cap without changing other
things (primary coil and/or top load) to keep it all in tune. How do you
know if the capacitor made the difference or the other thing(s)? If you
already have a .03uF cap, I would just go with that, otherwise you'll end
up building two completely different coils. But kudos to you if you do
that!
The mains-resonant (MR) cap size for a 15/120 NST @60Hz is .021uF, and
15/135 would be a tad larger, so .015uF is *smaller* than resonant. I'm
not sure that an MR size is something to avoid at all costs. It's only a
hazard if static gaps are opened wider than is safe, or if an RSG is used
without properly set safety gaps. The advice to avoid MR caps is
principally for newbies without the self-discipline and understanding to
avoid opening up the gap to the point of self-destruction.
Regards, Gary Lau
MA, USA
On Sat, Dec 23, 2017 at 9:55 AM, dennis otmaskin <dotmaskin@xxxxxxxxx>
wrote:
> Thank you Gary. I may want to experiment with the .015uF STR vs. the .03
> LTR to see how each plays out. If I did that, do you think the .015 STR be
> a safe value that would avoid capacitive resonance with the 15/135? Dennis
>
> On Fri, Dec 22, 2017 at 6:57 PM, Gary Lau <glau1024@xxxxxxxxx> wrote:
>
> > For the longest sparks, a Larger Than Resonant cap is recommended. The
> MMC
> > design chart recommends for a 15/120 60 Hz NST w/ static gap, a .03uF
> cap,
> > so for 15/135, you could even go a bit higher. Now LTR isn't the law,
> and
> > one may in fact deliberately choose a STR cap, as it will have a
> different
> > character of spark - shorter but brighter and more dynamic.
> >
> > Regards, Gary Lau
> > MA, USA
> >
> > On Fri, Dec 22, 2017 at 3:56 PM, dennis otmaskin <dotmaskin@xxxxxxxxx>
> > wrote:
> >
> > > Thanks Ian for your reply! What you say is encouraging to hear. If you
> > > don't mind, I have one more question...
> > >
> > > Java TC indicates, for my 15/135 NST, that Resonant Cap Size would be
> > > 0.0239uF. I understand that bad things happen when using resonant cap
> > > size. So I'm trying to decide on whether to use a 0.03uF cap or a
> > .015uF.
> > > I've got one of each. The .03 cap is pretty close to the indicated
> .0358
> > > LTR Cap Size for a static gap. On the other hand if I plug the .015
> cap
> > > into Java TC, it shows a dramatically greater rate of Breaks Per Second
> > and
> > > possibly a few more inches of spark length. My question is is there
> any
> > > potential problem with resonant rise with the .015 cap. I.e., is the
> > .015
> > > cap value far enough from the resonant cap size to be safe?
> > >
> > > Thanks again for your help, Dennis
> > >
> > > On Thu, Dec 21, 2017 at 11:55 PM, Ian McLean <austesla@xxxxxxxxxxxxxx>
> > > wrote:
> > >
> > > > Hi Dennis,
> > > >
> > > > If you have proper RCD¹s installed, it is unlikely you will trip a
> 15A
> > > > circuit with 18A at least for the sort of runs lengths you do on a
> > Tesla
> > > > coil.
> > > >
> > > > I regularly ruin my tube coil at between 30A-40A from a wall socket.
> > The
> > > > RCD is only 20A, but it has never tripped even with a 2 minute run.
> > > >
> > > > Cheers,
> > > > Ian
> > > >
> > > > On 22/12/17, 2:40 pm, "Tesla on behalf of dennis otmaskin"
> > > > <tesla-bounces@xxxxxxxxxx on behalf of dotmaskin@xxxxxxxxx> wrote:
> > > >
> > > > >Hi I'm hoping someone from the list can offer advice some advice and
> > > > >suggestions. I am replacing the 15/60 NST on my current static gap
> > coil
> > > > >with a de-potted NST with some shunts removed so that it puts out
> > > 15000v @
> > > > >135mA.
> > > > >
> > > > >Running different designs on Javascript Coil Designer, I'm finding
> > that
> > > > >the
> > > > >Effective Input Current (current draw?) runs over 18 rms amps. My
> wall
> > > > >outlets in the garage are all 15 amp. So if I'm understanding this
> > > > >correctly, it looks like I would be constantly tripping the circuit
> > > > >breaker
> > > > >when running the coil at full variac voltage. I've run different
> cap
> > > > >sizes
> > > > >through Java TC but cant seem to get around the 18 amp draw.
> > > > >
> > > > >To get the current draw to just below 15 amps, I would have to dial
> > the
> > > > >variac down to 106 volts which would reduce the spark length
> > > > >substantially. I'm thinking that I am pretty much stuck with a
> > systems
> > > > >that is limited to 106 volt input. Do you think this is the case?
> > I'm
> > > > >hoping that I don't have to rewire my garage outlets for 20 amps
> just
> > > for
> > > > >my coil. Any suggestions would be most appreciated.
> > > > >
> > > > >Thanks, Dennis
> > > > >_______________________________________________
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> > > >
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