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Re: Rotaty popping, (Was Re: commercial cap failure)

In a message dated 4/24/00 1:03:26 AM Pacific Daylight Time, tesla@pupman.com 
writes:

snip

<< 
 I've noticed that some coilers have excellent results using welders,
 whereas others have better results with variacs as current limiters.
 Two thoughts here;   1) the welders which allow for an infinitely
 adjustable inductance may provide better control than a welder 
 which has a selectable inductance (with no steps between the
 selections).    2) anyone who has excellent results using a welder
 with selectable inductances, may have lucked out with the cap size
 vs. available selectable inductance values perhaps?  
 
 The variac has the advantage of providing for an infinitely adjustable
 inductance value (as compared with the selectable or stepped type
 of welder).  Some folks have had problems with saturation
 in the variac.  This would depend on the number of turns in use and
 the voltage being dropped across those turns, etc.  Some folks like
 to cut the variac core to create a slot, etc.  I've never had good results
 adding resistive ballast to my TC's.  The addition of a resistance tended
 to reduce the performance but did not make the coil run smoother.
 
 Cheers,
 John Freau
  >>
John,

As an addition to an earlier reply of mine, I am a couple of days behind here 
- the 5,000 watt variac that I am using as ballast for my 5kva transformer, I 
believe is saturating.  It is rated for 120 volts, 5,000 watts which should 
be good for about 40 amps.  My typical primary current is around 30 amps.  It 
does groan a little however.  I really don't want to cut the core.  An 
interesting thing to note is that the best performance from the coil does not 
come from a particular tight setting on the ballast variac.  I now have it 
set about in the center, and it really does not change the performance if I 
move it either way up to maybe 25%.

Again, the reason I went to the variac instead of the welder was to prevent 
an unwanted 60 HZ resonance that was causing extremely high primary voltages 
and destroying my caps.  The variac also fixed the problem of the popping 
sound in the rotary.  My original configuration with the welder and using 
about 1.5 ohms of series resistance also seemed to run better at lower welder 
settings, which would be with higher inductance.  I haven't measured the 
inductance of the variac, but I would guess from looking at it that it would 
be considerably less than the welder.

Ed Sonderman