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Re: CD 942 failure tonight



Original poster: "John Richardson" <jprich-at-up-dot-net> 

Hi Malcolm,

I do have resistors across each cap.  I made a video this evening, albeit a
rather poor one, of my set up as it was when the first fire was initiated.
So far three caps in succession.  Terry has been kind enough to check out
the video and the three (thus far) blown caps.  I'll have his package in the
mail tomorrow.  I would like to thank Terry, Dr R., and everyone else who
has offered advice.  Hopefully Terry will be able to enlighten us after he
checks out the video and the capacitors.

Thanks,
John
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Monday, March 01, 2004 10:04 AM
Subject: Re: CD 942 failure tonight


 > 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
 >  >
 >  >
 >  >
 >
 >