RE: Re[TCML] NST rebuild good

["Lau, Gary" <Gary.Lau@xxxxxx>]

If I go back to the original post, you're using a .033uF cap with a rebuilt and deshunted 15/120 NST and a 120BPS sync RSG.  The problem is that the capacitor is much too small for this configuration, resulting in the cap charging to a too-high voltage and self destruction and safety gap firing.  With a static gap, if the cap is too small, the only consequence is that the gap fires more often but at a safe voltage determined by the gap width.  With a SRSG, the cap is free to charge as high as it cares to; it's up to you to choose a value that limits it to a safe voltage.  With my 15/60 NST and SRSG, I've found that a .04uF cap is optimum, so you could go at least 2-3X larger and maybe more considering the deshunting.

The calculation of the max voltage based on the applied 80VAC isn't at all that simple.

Regards, Gary Lau
MA, USA

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of mark olson
> Sent: Thursday, January 10, 2008 7:05 AM
> To: Tesla Coil Mailing List
> Subject: Re: Re[TCML] NST rebuild good
>
> Hi Bart,
>
> >Hi Marko,
> >
> >I'm having trouble sending out emails from my home pc. Server is having an
> >issue (I think). Anyway, thought I would send via web mail.
> >-------------------------------------------------------------------
> >Ok, I see this is a propeller gap. I take it the center tungsten rod is
> >the green stripe type?
>
> The tungstens are 2% thoriated, red tip.
>
> >I imagine this rod is spun around from a motor
> >shaft directly under and center to the rod?
>
> Yes, actually two rods so that the diameter described by the flying
> electrode is 12"
>
> >Your gap spacing looks fine
> >on the main gap. The gap actually looks fine and I would think it should
> >be working ok. The only thing that I can see as a possible problem is if
> >the motor is synchronous and is not phased correctly or drifting.
> >
> >If this is a synchronous motor, is it AC or DC? Some motors do have
> >drift, so I wonder if that is happening? If your phasing, how are you
> >performing it (variac? physical?).
>
> The motor is a salient pole 1800 rpm.  I am controlling the synchronization
> with a small variac wired as an
> inductor with a phase shift capacitor across the motor.
> When the rotary gap was tested with only the NST  connected,  the arc in
> the gap could be changed
> from firing just before closest proximity to stretching the arc to about 30
> degrees after closest proximity.
> It appeared to control quite consistently under this test, which is the
> only one I could think of.
>
>
> >Take care,
> >Bart
>
> I am really starting to believe that the capacitors that I have left after
> blowing up half of them, simply are not up
> to the task, as the calculated voltage across the string should not exceed
> 23kv. At 80v into the NST,
> calculated 11.3kv rms out,  Do see where I am going with this? Or do you
> think I am off track?
>
> Thanks,
> Marko

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