[TCML] First light (maybe second light) on mid-sized coil

[David Rieben]

Hi Gary,

Thanks for the input. Actually, I didn't necessarily mean to imply that
this was "abnormal" behavior, though, just that 80 nFd is a pretty big
honking capacitor to run on a standard 120 volt feed. I agree that there
is probably core saturation and ferroresonance going as you stated but
it seems to continue somewhat after the SG starts firing, too. Of course,
the BPS rate is NOT going to be very high with 80 nFd either. I'm still
wondering if enough PFC caps in parallel with the input to the PT would
help to reduce the current draw at all or does this approach only
work significantly for NST powered coil? I know most pig coilers
do not bother with PFC caps (myself included) since available current is
not near as limited with a 60 or 100 amp, 240 volt service.

David Rieben

----- Original Message ----- 
From: "Lau, Gary" <Gary.Lau at hp.com>
To: "'Tesla Coil Mailing List'" <tesla at pupman.com>
Sent: Wednesday, April 16, 2008 6:39 PM
Subject: RE: [TCML] First light (maybe second light) on mid-sized coil


Hi David,

I think there is nothing abnormal with what you described.  It's just not a 
healthy thing to do.  I haven't tried it myself, but if the Variac is 
adjusted to just below the point of firing, it means that the transformer is 
constantly charging and discharging the cap to just below the firing 
voltage, but since the gap never fires, that energy is constantly being 
traded between voltage on the cap and current in the transformer secondary, 
likely to the point of core saturation and ferroresonance.  If the Variac 
were just a bit higher, the gap would fire and the capacitor energy from 
each charging cycle would have a place to exit rather than causing the high 
current and avoid this problem.

Regards, Gary Lau
MA, USA

> -----Original Message-----
> From: tesla-bounces at pupman.com [mailto:tesla-bounces at pupman.com] On
> Behalf Of David Rieben
> Sent: Wednesday, April 16, 2008 7:50 PM
> To: Tesla list
> Subject: [TCML] First light (maybe second light) on mid-sized coil
>
> Hi all,
>
> I have figured out that the real current hog culprit in this coil project
> is the 80 nFd primary cap. I realized that as I turned the variac
> up to only 30 on the dial, the SG is just at the threshold of be-
> ginning to fire intermittently. If I turn the variac to this point and
> stop just before the SG starts to sputter and leave it powered up
> in this position for a couple of minutes, the 22 amp Staco variac
> will still manage to get pretty warm and if left long enough, it will
> even begin to smoke! I assume this is just the primary capacitor
> load on the transformer as the SG is not even firing yet! Am I go-
> ing to have to settle for  a smaller primary capacitor to stay happily
> within the bounds of a 120 volt, 20 amp service or just say the heck
> with it and upgrade this baby to 240 volt service? Any suggestions?
>
> David Rieben
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> Tesla at www.pupman.com
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