[Amps] Re: Step-start calculation

[Will Matney]

I thought I ought to give a link to the following PDF file by Potter & 
Brumfield about the effects of using a zero-crossover switch with 
transformers. From this, I think most will see how and why surge 
currents act. Also, see the references (footnotes) on page 2.

Link;   http://relays.tycoelectronics.com/app_pdfs/13c3206.pdf

Will Matney


Dennis12Amplify at aol.com wrote:

>In a message dated 11/21/04 1:11:18 PM Central Standard Time, 
>wa1hco at adelphia.net writes:
>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
>***Jeff,
>
> ***Thanks for the education.
>
> ***I still find it very hard to believe that there can be an almost 
>instantaneous change in the secondary current when the secondary inductance is 
>probably measured in multiples of HENRYS, and I know it's been a long time since I 
>worked in that area, but when I did, I rarely saw 'M' values greater than .85 
>for a high voltage step up transformer.
> The turns ratio is a big part of the problem in this case, because the ratio 
>is so high, it is very hard to get a coefficient of coupling much higher than 
>that. Maybe the technology has changed and that is no longer the case.
>
> ***Now if that same transformer was bifilar wound with a 1 to 1 or even a 4 
>to 1 ratio I would understand completely and absolutely agree with you.
>
> ***If what you are saying is true, then wouldn't the reciprocal also be true 
>and allow me to greatly extend the frequency range of my tube stereo output 
>transformer by making my speaker load impedance as low as possible; like 
>paralleling ten 4 ohm speakers for an output load of only .4 ohms on the secondary 
>of the output transformer? 
> I understand that the efficiency would be poor unless the turns ratio was 
>readjusted, but the audio bandwidth should be HUGE!
>
> ***I guess the best way to test this concept would be to run a 
>'significant', (like 1 ampere for a high power linear amplifier transformer), amount of DC 
>current through the secondary winding, then short the primary and open the 
>secondary circuit. If what you say is true, there should be no high voltage spike 
>when the secondary discharges because of the shorted primary and the perfect 
>coupling. I, personally, would not want to be holding both ends of those 
>secondary leads while they were being open circuited......
>
>***Regards,
>
>***Dennis W. Ostrowski
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