RE: NST current, was Filters & Chokes

["Lau, Gary" <Gary.Lau-at-xxxxxxxxxx> (by way of Terry Fritz <twftesla-at-xxxxxxxxxx>)]

With 140VAC in and a shorted output, my 15/60 puts out something like 70mA.
It's only when it's running with a capacitive load above 120V in that the
output currents take off.

Gary Lau
Waltham, MA USA

>Original poster: FutureT-at-aol-dot-com
>Gary, all,
>
>I use a 12/30 NST with LTR cap, and it pushes about 50ma, but this
>only happens if I turn up the voltage to 140volts input using a step
>up type variac.  I seem to remember that you're using a step up
>variac also?  With a normal 120 volts input, my NST just gives the
>rated 30ma to the coil.  But if I use a matched size cap, then I can 
>get 50ma with just 120 volts input.  I haven't tried 140 volts into a
>shorted output NST to see what the current is.  The 140 volts input
>probably has a lot to do with increasing the current.
>
>John Freau

>>  I use a standard unmodified 15/60 NST and the filter uses a pair of 1.6K
>>  113W resistors.  For a very long time I was puzzled at just how hot
these
>>  got.  By standard logic, the power is I^2 R, or .06^2 * 1600 =
5.76Watts.
>>  But after building a fiber-optic VI probe, I was able to scope the NST
>>  secondary current with a digital scope, which also performs true-RMS
>>  calculations.  Guess what?  My 60mA NST is pushing 184 mA, RMS.  It
appears
>>  that some unexpected things happen when charging an LTR cap, speculation
is
>>  that the current shunts saturate and allow far more current to pass.  So

>>the
>>  184 mA causes a dissipation of 54 Watts per resistor.
>>  
>>  Gary Lau