[Amps] Re: Step-start calculation

[jeff millar]

PSU designer (http://www.duncanamps.com/psud2/download.html) can do this 
calculation and I've got it running here.  The model needs some values 
for various parameters.  Here's some results for some sample HVPS with 
zero voltage switched

Case 1:
    Transformer
       1500V secondary, 10 Ohms
        240V primary, 0.1 Ohms
    Full wave doubler
       40 uF caps (2)
    Results
       4K load impedance
       Output ripples from about 3900 to 3700 (~5%)
       Peak current at turn on 27 Amps
       Peak current on each line cycle 9 Amps

Case 2:
    Transformer
       2600V seconday, 10 Ohms
       240V primary, 0.1 Ohms
    Full Wave Bridge
    40 uF cap
    Results
       4K load resistance
       Output ripples from about 3500 to 3300 (
       Peak current at turn on 42 Amps
       Peak current on each line cycle 6 Amps
  
Adjusting parameters and generally looking at result shows
    Magnitude of turn on current surge mostly depends on capacitance
    Transformer resistance has little effect (surprise!, change values 
about 20%)
    Peak current at turn on of 5-10 times cycle to cycle peak with 
enough capacitance to limit ripple to 5%

Conclusion...
    Zero voltage turn on works
    Keep the capacitance low (good idea anyway to limit flash over damage

If anyone wants to run the model with different values just send me an 
email.  Or if you get some interesting results, please post them.

jeff, wa1hco
  
Roy Koeppe wrote:

>I don't like to think about it. I gives me a headache.
>
>73,    Roy         K6XK
>
>
> "...What would be a suitable
> value of step-start R to limit the inrush current to 50A-rms?..."
>
>
> In this practical & real world, it would be 4.6 ohms.
>
>Congrats, Roy.   The closest value in my junk box was 5.6½s.
>
>2nd question:  What would the approximate inrush-I be without a
>step-start relay and resistor?
>
>cheerz
>
>
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