[AMRadio] Ferroresonant transformer revisited

Rick Brashear rickbras at airmail.net
Sun May 7 12:26:57 EDT 2006

    Jim, Geoff, Bob, John and all who responded, thanks for the 
excellent information.  I scoped the output of the transformer and it is 
without doubt NOT a sine wave, Jim.  Like you said, it is almost a 
square wave.
    Bob, I think I have a couple of those old television transformers I 
pulled years ago when  I was in the service business.  I'd forgotten all 
about that, thanks for the memories.
    Geoff, I am inclined to agree with you about the heat of the 
transformer.  I can touch it, but it would be very uncomfortable if not 
damaging to my hand to leave it on there more than a very few seconds. 
    I think maybe one thing I should consider is Bob's thoughts on how 
it's mounted.  I'm not sure what service it was in before I got it, but 
it was likely from a battery charger of maybe even a small arc welder.  
It was mounted on a heavy 13" X 19" X 1/4" aluminum plate which I'm sure 
helped dissipate the heat.  I have it mounted on a 12" X 10" X 3" 
aluminum chassis which would not be nearly as effective.
    The output is very clean.  I'm using 3 - 71,000 mfd @ 25 vdc 
capacitors in series, computing to about 23,600 mfd worth of filtering.  
There were four of the caps originally, but one went south before I got 
the piece.
    Jim, correct me on my math if I am heading the wrong direction.  
Since I don't have a true RMS voltmeter can't I take the square root of 
the power dissipated in a resistor across the output to find the actual 
RMS voltage?

Thanks again to all for all of the great response and advice.

Jim Candela wrote:

>    The ferroresonant transformer is not really
>resonant at all since the winding that feeds the
>capacitor is wrapped around....

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