[Amps] Re: Step-start calculation

[R.Measures]

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



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