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Re: [Amps] Re: Step-start calculation

To: jeff millar <wa1hco@adelphia.net>
Subject: Re: [Amps] Re: Step-start calculation
From: R.Measures <r@somis.org>
Date: Sat, 20 Nov 2004 09:43:14 -0800
List-post: <mailto:amps@contesting.com>
Jeff ---- Here are the needed parameters: C is two, 93uF in a FWD. The mains R is 0.127-ohms, xfmr primary winding R = 0.059-ohms. The transformer sec. potential is 3200V-rms, Rsec = 16.5-ohms. The load at switch-on is 2.2M-ohms (the 22, 100k equalizer resistors).

I do not see how this computer app. could calculate inrush-I without knowing the mains ESR?

On Nov 20, 2004, at 9:04 AM, jeff millar wrote:

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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Richard L. Measures, AG6K, 805.386.3734. www.somis.org




Richard L. Measures, AG6K, 805.386.3734. www.somis.org _______________________________________________
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