Re: CD 942 failure tonight

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

Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

Hi John,
         Do you have a resistor across each cap (I am not saying this
is part of the problem! - I am digging for further information). If
so, check their ratings are sufficient for the voltage being applied
across them and check that none have gone high-resistance or open
circuit. If you don't have any resistors in your MMC, you may being
experiencing a problem with mismatched capacitors.

Malcolm

On 28 Feb 2004, at 18:31, Tesla list wrote:

 > Original poster: "John Richardson" <jprich-at-up-dot-net>
 >
 > Hello,
 >
 > Copnsidering the recent MMC debate,  I figured that I would share this
 > evening's run.  This is a first fire, and tuning was done at partial
 > variac setting.  Volt and amp meters are not in yet, so I can't give
 > any real numbers.  Also, SRSG was set using a flourescent bulb, as I
 > am still waiting on my motor run caps for John's phase controller.
 >
 > Here are the specs:
 >
 > Topload: 4x24  Soon to have an additional 4x36 on top of it.
 > Secondary:  4.5 OD PVC with 36" of heavy build #24, 1481 turns.  Plan
 > on an 8" with an 8 by 36 toroid in the future. Primary:  .25 Cu
 > tubing, .25 between turns, 16 turns total, seems happiest tapped at 6
 > and 5/8 turns. Gap: SRSG Safety across RSG:  Set at .5" NST safety
 > gap:  5/8" Trans:12000/120 NST Capacitor bank:  4 strings of 9, total
 > of .0667, per MMC chart.
 >
 > After rough tuning and ramping up variac, I heard one cap blow.  Black
 > soot and a hole about a quarter inch deep.  Soldered up a new one, and
 > ramped variac up to 120 volts.  Sparks about 4 feet, and gap won't
 > fire until variac is above 60%.  After that it will fire all the way
 > down to about a quarter turn on the variac.  Checked rotary, and there
 > is no follow around with the gap arc.  She fires right on electrode
 > alignment, so I am assuming that phase is pretty close.  Started it up
 > again, and tried to fine tune.  A half turn either way from the tap
 > point of turn 6 5/8 and performance diminishes.  Put tap back at this
 > point and fed the trans the full 120 volts.  I stopped things again to
 > check everything out.  First I checked the variac, an ancient Ohmite,
 > to see if it was getting warm.  It's only rated for 10 amps, and I
 > made a new brush out of a piece of brass due to no access to new
 > parts.  Everything looks good and runs cool.  The  lash up wiring to
 > the coil primary is 14 gauge, and it is hot to the touch, and the
 > primary is warm.  Will go to #8 for final set up.  Looked at cap bank,
 > and the new cap looked like a piece of popcorn that had just popped,
 > black and all.  The one on the next string over was bulging like you
 > know what, but no black stuff.  I can see the foil, however.
 >
 > Why is this happening?  I am not going to re-fire the system until the
 > last portion of the tank wiring is replaced with #8, PFC caps and
 > meters installed, phase controller up and running, and new toroid
 > installed.  I've put lots of work into this thing, including welding
 > up a nice stand for the controller, gap, trans and cap assembly, and
 > want to get to the bottom of this cap problem.  Any thoughts?
 >
 > Thanks,
 > John Richardson
 >
 >
 >