RE: [TCML] Nearly First Firing

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

Hi Simon,

OK - it's clear that the cap value is not excessively high.  For an 8/50 NST @50Hz, a mains-resonant cap would be .02uF, so for an LTR design one would shoot for .03-.04uF.  I think you presently have .016uF.

So the NST looks good, but I'm not so sure about the caps.  Are your caps disk capacitors?  Ceramic caps are rarely suitable.  Some doorknob caps are, but disk caps are never suitable.  They tend to have high losses and consequently get hot, quickly, and die.  And the temperature coefficient is awful, and change value as you look at them.  Is it possible that one or more of them is shorted?  It's not a definitive test, but what does an Ohmmeter read across them?

Regards, Gary Lau
MA, USA

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of Simon Dodd
> Sent: Thursday, January 22, 2009 5:21 AM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] Nearly First Firing
> 
> Ok, I just got an answer back from Tunewell and it turns out my
> transformer is only 8Kv @ 50mA!  I will be adding the relevant caps to
> my MMC and hopefully the rain will stop so I can try for test firing 2
> tonight! Hopefully with pictures or videos for you all to see!!
> 
> On 21 Jan 2009, at 20:20, Simon Dodd wrote:
> 
> > Cheers Gary,
> > Its a conventional heavy core transformer as far as I'm aware. It is
> > an old one and its very heavy!!   The caps are high voltage ceramic
> > caps from rmcybernetics.com
> >
> > Thanks
> >
> > On 21 Jan 2009, at 20:06, Lau, Gary wrote:
> >
> >> Is the NST a conventional, heavy core and coil transformer or a
> >> lightweight solid state inverter type?  You need the core and coil
> >> type.
> >>
> >> What kind of caps are these?
> >>
> >> Regards, Gary Lau
> >> MA, USA
> >>
> >>> -----Original Message-----
> >>> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> >>> Behalf Of Simon Dodd
> >>> Sent: Wednesday, January 21, 2009 2:42 PM
> >>> To: Tesla Coil Mailing List
> >>> Subject: [TCML] Nearly First Firing
> >>>
> >>> Hi Guys,
> >>>
> >>> I went for first light this evening!! Unfortunately there was
> >>> nothing!
> >>> My spark gap fires when there is no capacitor bank in place but as
> >>> soon as I put my MMC into the circuit and connect the main parts of
> >>> the coil, the spark gap stops firing :-(  I am using a 10Kv NST
> >>> with a
> >>> static spark gap and 16, 20Kv 1000pf capacitors in parallel. These
> >>> are
> >>> from the calculations on deepfriedneon.  The spark gap will fire if
> >>> the lead to the outer ring of the primary is left unconnected.
> >>>
> >>> Im sorry its not too clear, I can do a quick diagram if you want
> >>> more
> >>> info.
> >>>
> >>> Thanks for your help again
> >>>
> >>> Simon

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