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previous: Stephen Conner Thanks for that interesting piece o... -- 5/6/2000 11:30 PM View Thread

Re: more on donuts, current-inrush, and CIL's

5/7/2000 3:58 PM
Ken Gilbert
Re: more on donuts, current-inrush, and CIL's
"You could probably do with some kind of soft-start device for your BAGA if you haven't got one already."
yeah, actually i did, but i kind of did it ass-backwards. i knew i was drawing huge currents on start-up, but i assumed it was due to the 1000 mics of filter capacitance charging up to 620vdc.. that alone sends a pretty big spike down the line. so, going on that assumption, i ordered a CIL from allied electronics, and sized it for the SECONDARY of the plate tranny--something like 120R cold, 2A nominal current. to make a long story short, it WAS enough to stop blowing mains circuit breakers, which was good enough for me. it's really a pain in the ass to have to go find the breaker box in the building you're trying to play in.  
after that point i discovered that even though the large filter cap bank wasn't helping things at all, it wasn't the primary cause of the problem. since the primary of the PT draws a lot more than 2A, i couldn't put it there, so i left well-enough alone. next time, though, i'll use the CIL on the primary, where it really belongs. live and learn, right?  
also, as a general side note:  
be sure you have a MOV or snubber network across the primaries of your transformers... put this between the main power switch and the winding itself. like any other inductive load, the inductance will attempt to keep a constant current flowing through the primary. therefore, when you open the power switch, you can get a VERY big voltage spike transient across the primary winding as it soars to V = -L (di/dt) [where V is volts, L is inductance in henries, and di/dt is the rate of change of current, in amps/second]. when you open the switch, you effectively introduce an infinite change of current. do the math to see where V ends up ;-)  

Stephen Conner q{do the math to see where V ends u... -- 5/8/2000 11:06 AM