[Amps] Fw: Step Start on a 3KA Amp

[Tom W8JI]

> I tried the zero crossing switch on two HV power supplies 
> (8877 and GS35B), both power up just fine, nice and quiet, 
> no blinking lights.
>
> Using a zero crossing switch makes a significant 
> difference compared to closing the switch when the line is 
> not zero. Closing the switch at zero allow the output 
> capacitance to charge as the line voltage rises to peak, 
> following the curve of the sine wave.

If your supply fully and smoothly charges in one quarter 
cycle and only draws 20 amps while doing it that is a 
miracle Jeff. You either have a supply with horrible ESR or 
you are missing something.

Since the power factor of the supply is not zero, peak 
current does not occur on switch closure even at the sine 
wave crest. Peak surge would occur when you close the switch 
before the line voltage crest is reached.

With a 2.4kV transformer having 15 ohms ESR,  20 uF charged 
to about 3300 volts calculates to be about 24 amperes first 
half cycle surge into the capacitor. Line current (assuming 
perfect power line) would be 10 times that value, or 240 
amps.

We don't eliminate inrush by starting at zero. What we need 
to do is ramp it up with a gating system, or start it 
through a resistance and then switch the resistance out.

73 Tom