Re: It Just Stopped

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Sean Taylor" <sstaylor-at-uiuc.edu> 

Hi Matt,

Assuming both the NSTs are fine past 6000 Volts (IE no internal arcing that 
starts at around 6,500 V :-) ), then I would guess your cap failed to a 
short.  Even though you're measuring something at low voltage, there may be 
carbon tracking that is shorting the cap out.  LCR meters are typically 
designed to measure capacitances with a series or parallel resistance so 
it's possible a ~10 kOhm resistance is effectively shorting your cap 
causing the meter to read approximately correctly, but the cap to 
effectively short your transformers.  Check the DC resistance of your cap 
(after shorting it to make sure there is no charge), and the meter should 
go to showing and open circuit.  However, the 0.5% change you show in the 
capacitance isn't very much and could easily be the temperature affecting 
the meter and/or capacitor.

I think most people would say that using that cap with a 15 kV transformer 
(and at that current) is pushing it a bit (if that's one of the 37667 caps 
- 35 kV, 30 nF).  I would build an MMC for that set up with 2 strings of 10 
caps each of the 0.15uF, 2 kV CDE 942C series caps.  Unfortunately, since 
The Geek Group is out of them right now, you'll have to find another source 
such as Richardson Electronics - http://www.rell-dot-com.  I haven't ordered 
from them in quite a while, but when I did, it took about 2 months to get 
the caps, and there was a minimum order of 27 or so caps.

Before you order new caps though, you may want to use a string of diodes 
and charge your cap up to 20 kV or so and see if it holds a charge, or 
requires excessive current in to maintain that charge.

Good luck figuring it out!

Sean Taylor
Urbana, IL

On Mon, 02 Aug 2004 18:10:23 -0600, Tesla list <tesla-at-pupman-dot-com> wrote:

>Original poster: Mddeming-at-aol-dot-com Hi All,
>      Something happened last night that has me puzzled. I was testing 
> 4.25" coil. It had been run intermittently for about 1/2 hour. I fastened 
> a pointed rod to the center bolt of the topload (dual toroids) pointing 
> upward, preparatory to making a "pinwheel". I was getting nice 3ft+ arcs 
> to the ceiling of the lab, (coil is caged 10' x 9' x 8'.) After about a 
> minute, it suddenly went dead. No arcs, no gap spark, no sound except the 
> vacuum on the sucker gap. It had been drawing ~18 Amps on 30 Amp circuit 
> prior to problem. Indicator lights showed power reaching primaries of 
> NSTs. Variac output showed 120V. No racing sparks noted, no arcing to 
> primary. I shut system down, waited ten minutes, tried to restart... Nada!
>      I disassembled everything and checked each component:
>
>Xfmr 1 Allanson 15/60:  6000v left and 5990v right to ground terminal with 
>102V input. (My HV meter limit is 6 kV)
>Xfmr 2 Transco 15/60: 5995v left and 5980v right to ground terminal with 
>101.8v input.
>Tank cap: Maxwell 37xxx series, 30 nF nominal,. measured 29.95nF with 
>RdShk DMM and 30.91 on AADE L/C II-B. On the 14th of July, it measured 
>31.07nF on the L/C II-B when air Temp was 11F warmer and Humidity was 30% 
>higher.
>Sucker Gap 1 HP vacuum spaced 7.5 mm.
>Safety Gap spaced 5 mm Left and 4 mm Right.
>
>      Reassembled everything and... Nada!!
>
>Any Guesses??
>
>Matt D.
>