[Prev][Next][Index][Thread]
Re: Advice needed on capacitor tests: update: BIG resonance
Hi Alex,
> Original Poster: Alex Crow <user-at-alexcrow.clara-dot-net>
>
> Dear all,
>
> I will add to this after another test....
>
> I hooked up my cap across my NST again, but this time put my multimeter on
> the output of the NST. I turned up the voltage, and at only 1 or 2 percent
> of line voltage I was getting about 600-700 volts on the meter!! I tried
> it without the cap and all I was getting was around 80-100 volts on the
> same setting... All I can think of is that the NST windings are resonating
> with my cap at 60Hz and causing this voltage rise of about 6 to 8 times!!
> Instead of shunts, these things have a small gap in the core which provides
> enough leakeage inductance to limit the current.
>
> In fact, I'm just doing the test again right now - with the cap connected I
> set the variac for an NST output of 800V. I removed the cap and I'm only
> getting about 85V. This must mean that I was actually getting about 10kV
> across my cap, no wonder I got the big sparks! this is a rise of nearly
> 10x! Help!!! does this mean my xfrmr is useless for Tesla work? I can't
> see that my RC filter (desingned for the Tesla frequency) is going to stop
> this!
>
> Please respond, I am at my wit's end as to what to do - can I fill the gap
> in my core and add limiting on the input to my NSTs? maybe this would
> reduce the inductance and stop the ringing. Help!
The trick is to set your gap at a voltage your cap can withstand
under running conditions and no more. Your transformer is fine. Any
ballasted system that is mains resonant exhibits the same phenomenon.
Malcolm