Re: MMC problems

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

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

Hi Gerry,

I agree with the small topload train of thought.  4x24 is small for 1500
watts.  I am going to make an 6x32 or 8x32 soon.

The capacitance shouldn't have been too low, as 4 strings of 9 comes out to
about .0667 uF.  I do believe that the low number of tuning turns allowed
too much current per turn, and a large topload combined with an 8"ish
secondary will bring tuning to a greater number of turns, hence less stress
per turn and greater inductance.

As far as the safety gap, I think you are correct.  Terry gave me the specs
for the spheres the gap is made up of, and I set accordingly.  MUCH better
than the set it with just the NST method.

Still waiting for better weather to do some runs, though.  BTW, what kind of
performance increase do you think the 8x32 topload and 8" secondary (1480
turns of #24 heavy build) will provide?  My gut tells me it should be
substantial.

Thanks,
John Richardson

 >
 > Hi John,
 >
 > I believe you had a multitude of problems that resulted in the failure.
 >
 > 1. Your top load was too small (maybe way too small) - resulted in the
 > number of turns for the primary being too low.
 >
 > 2. Your Cp was too low - allowed the voltage on the Cp to get too high.
This
 > coupled with low number of turns on primary allow peak currents to be
 > greater than expected.
 >
 > 3. First time around, I think your safety gap was not doing its job and
this
 > enabled the high voltages that #2 resulted in.
 >
 > With properly sized Cp (to keep the voltages reasonable in conjuntion with
a
 > properly set safety gap),  you need to increase the topload capacitance to
 > keep the number of primary turns reasonable to limit the peak current.
 >
 > Also, spreading the current between two strings (instead of one) will
help.
 >
 > Gerry R
 >
 >
 >  > Original poster: "John Richardson" <jprich-at-up-dot-net>
 >
 >  > I finally got my meters in place, and can give some more info into what
my
 >  > coil is drawing.  Again, these are short runs, as I can't run things
 > outside
 >  > yet.  For anyone who may not remember, I had the caps blowing on my
 >  > 12000/120 system, and excessive primary heating.  I hope to run for an
 >  > extended period in the next day or so, weather permitting, but for now
all
 > I
 >  > can say that at exactly 119 volts in, with no PFC, I am pulling well in
 >  > excess of 15 amps from the wall.  I can't be any more accurate than
that,
 > as
 >  > 15 amps is the max this meter will measure, and the needle is beyond
 > pegged.
 >  > With 300uF PFC, I am pulling between 12-13 amps from the wall.  This
 > sounds
 >  > right to me, but maybe others can shed more light.  I really expected
the
 >  > trans to be pulling more, thinking that this may explain why caps have
 > been
 >  > popping and things heating (ie trans outputs more than expected).  Will
 > have
 >  > more info soon.
 >  >
 >  > Thanks,
 >  > John Richardson
 >  >