Re: Scoping and cap charging

In a message dated 99-06-24 05:15:30 EDT, you write:

<< Hi John:
> With a NST system, how does one scope the cap charging voltage?  Even if
> using a high voltage probe, it still needs to be referenced to ground, and
> neither side of a cap is typically grounded.  I really need to see what my
> static gap BPS and charging voltage is.
Hi Gary,

I ground the case of the NST to house ground, and I ground the 
scope HV probe ground lead to the NST case also, so my voltages
are across 1/2 of the NST (and 1/2 the normal amplitude). 
> Don't forget, I'm using a static gap, so my firing voltage is the same as
> with my reso-cap, and I suspect my gap firing is happening at random and
> chaotic intervals.  But there is certainly something strange going on.

If the non-firing voltage is lower than the firing voltage, then that may
explain why static gaps sometimes just stop firing when they're too
wide; once they stop, the voltage goes lower and can't refire them.  I
agree static gap operation tends to be chaotic. 

> just metered my NST input current (excluding my vacuum motor), and it's
> pegging a 20 Amp meter, and tripping a 20 Amp breaker after about a minute
> of run time.  This with just one 15/60 NST!  I'm trying to find or build an
> AC meter to monitor the NST secondary current, this may ultimately explain
> my hot resistors.

Are you using a PFC cap on NST input, if not, that may help.  

John Freau

> Regards, Gary Lau
> Waltham, MA USA >>