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Re: My PT is loud!

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Tesla729-at-cs-dot-com>

In a message dated 2/21/01 7:15:10 AM Pacific Standard Time, tesla-at-pupman-dot-com 

<< I 
< noticed that if i got the capacitance way too high, and i turned up the 
< variac to the pt, no sparks would jump the 1/2" saftey gap on the pt. It 
< worked with a 16 wine bottle salt water cap! When i turned it up to around 
< 60% A really loud buzzing/humming noise would come from either the PT or 
< capacitor, which i have watched vibrate voilently before. It would stay 
< until i turned everything off. >>


When you run your capacitor too large for the transformer, the transformer is
unable to fully charge the capactior within each half of the 60 Hz duty cycle.
This means that your tranformer sees the capacitor as an oversized load for
it, and basically a short. That, in addition to the fact that you are 
nearly triple its rated input voltage, will definitely cause your 
core to saturate and hence, the loud 60 Hz. hum. Although PTs are built like
Ft. Knox, they are still not designed to be voltage overdriven this way and 
probably eventually end up smoking it if you keep running it like this. The 
ternal ballasting that you are using will probably keep it from being 
overcurrented, but that 300 volts in where it's supposed to be 120V is 
overvolting it and will likely shorten its life expectancy :-( As one of the 
list members said, if it's rated at 120 volts input, you probably shouldn't 
put in
over 140 to 160 volts, tops. I would try to get by with say, 150 volts in, 
and that 
would still give you over 5 kV output and then you could use those oversized 
caps, since a lower voltage can charge a capacitor whose size (uFD) is 
ly proportionate to the square of the voltage ( If you half the voltage, the 
cap size
must inreased four-fold to keep the same amount of energy).

Sparkin' in Memphis,
David Rieben