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Re: MMC problems

Original poster: "Gerry Reynolds" <gerryreynolds-at-earthlink-dot-net> 

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
 > 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
 > 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,
 > 15 amps is the max this meter will measure, and the needle is beyond
 > With 300uF PFC, I am pulling between 12-13 amps from the wall.  This
 > 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
 > popping and things heating (ie trans outputs more than expected).  Will
 > more info soon.
 > Thanks,
 > John Richardson
 > ----- Original Message -----
 > From: "John Richardson" <jprich-at-up-dot-net>
 > To: "Terry Fritz" <teslalist-at-twfpowerelectronics-dot-com>
 > Sent: Saturday, March 20, 2004 7:37 AM
 > Subject: Re: MMC problems
 >  > Hi Terry,
 >  >
 >  > I need to do two things before I can proceed any further.  I am still
 >  > waiting for my meters from All-Electronics, as I want to see exactly
 >  > this thing is drawing.  I think I might be surprised.  I also
 >  > some safety issues in the basement, as the coil was hitting an
 >  > five feet with just the addition of a roll of dryer tubing placed on
 >  > existing toroid, and a little re-tuning.  I had everything at what I
 > thought
 >  > was a safe distance from the lone wire running the edge of the basement
 >  > foundation, and a huge spark managed to find it within fifteen seconds.
 >  > When it did that, it blew (literally) the outlet for the fridge out of
 >  > wall on the floor above.  I can't have that.  I am going to use a
 >  > garage for further tests, or build one heck of a Faraday cage.  I
 > personally
 >  > think that this NST is putting out more than it should, and the
 > combination
 >  > of low primary inductance (tapped at 6.5 turns) because of the smallish
 >  > secondary and toploads is causing the heating issues.  I will know more
 > when
 >  > I get my meters in place.
 >  >
 >  > Thanks for your continued interest, and I will keep you posted ASAP.
 >  >
 >  > Thanks,
 >  > John Richardson
 >  > ----- Original Message -----
 >  > From: "Terry Fritz" <teslalist-at-twfpowerelectronics-dot-com>
 >  > To: "John Richardson" <jprich-at-up-dot-net>
 >  > Sent: Friday, March 19, 2004 9:00 PM
 >  > Subject: MMC problems
 >  >
 >  >
 >  > > Hi John,
 >  > >
 >  > > Did you ever get your MMC problem fixed?  If so, I will get your tape
 > back
 >  > > to you and all.  If not, let me know and we'll try to figure it out
 >  > further.
 >  > >
 >  > > Cheers,
 >  > >
 >  > > Terry
 >  > >
 >  >