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

[jeff millar]

Tom W8JI wrote:
> Hal,
>
> Unfortunately a zero crosser does not do anything for 
> inrush. It is good for the switch, but that's all.
>   
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.

In some modeling with a 4000V supply with 50 Ohms equivalent series 
secondary resistance and 20 uFd of capacitance, the single cycle peak 
capacitor current hit 21 amps compared to 80 amps if switched at the 
peak of the line. When drawing 1 Amp of plate current, peak diode 
current ran about 4.5 Amps.

The standard 1N4007 1 Amp diode has a rating of 30 Amps non-repetitive 
half sine peak current, well more than the 21 Amp stress of this example.
> To limit inrush you have to add series resistance so current 
> is limited over some time period.
>   
That reduces inrush further...but maybe more than necessary.

jeff, wa1hco