[Amps] Re: Step-start calculation

[jeff millar]

Dennis...

A transformer has inductance when open circuit, but when something's 
connected to its secondary, that impedance get transferred to the 
primary by the square of the turns ratio. So, when the transformer runs 
open circuit, a nearly infinite impedance gets transferred to the 
primary and it draw little current. When a transformer has a a load such 
as a resistor or discharged capacitor, then the primary impedance 
depends on the winding resistances, turns ratio and coupling coeficient. 
For most transformers one can model the coupling as perfect.

jeff, wa1hco

Dennis12Amplify at aol.com wrote:

>In a message dated 11/20/04 11:47:47 AM Central Standard Time, r at somis.org 
>writes:
>I do not see how this computer app. could calculate inrush-I without 
>knowing the mains ESR?
>***Wouldn't you ALSO need to know the Inductance of both the primary and the 
>secondary windings and the coefficient of coupling between them?
>
>*** I would guess that because of the large inductance associated with the HV 
>secondary winding, (which would be in series with the secondary resistance 
>and diodes when charging the caps), there could be a significant counter EMF 
>produced for any rapid changes in primary current, and that counter EMF should 
>greatly reduce the peak inrush current at turn on time.
>
>***Regards,
>
>***Dennis O.
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