Continued Problems (fwd)

To: "'Tesla List'" <tesla-at-pupman-dot-com>
Subject: Continued Problems (fwd)
From: Tesla List <tesla-at-stic-dot-net>
Date: Sun, 10 May 1998 22:31:45 -0500
Approved: tesla-at-stic-dot-net

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From:  Malcolm Watts [SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent:  Sunday, May 10, 1998 3:29 PM
To:  Tesla List
Subject:  Re: Continued Problems (fwd)

Hi Bill (Turbett),

> From:  fxphoto [SMTP:fxphoto-at-centuryinter-dot-net]
> Sent:  Friday, May 08, 1998 4:09 PM
> To:  Tesla List
> Subject:  Re: Continued Problems (fwd)
> 
<snip>
> >>  I am sorry that I do not understand the effect of the current control
> >> method that you are using has on Xc but it seems that Xc would change as you
> >> change the current output. If this is so, the capacitance would need to
> >> change according to the current output. Perhaps someone can jump in and
> >> explain this to me.
> 
> This is where my brain went dead. I was trying to ask about Xl and was
> typing Xc. Restated, I was trying to find out what effect the additional
> inductance of the current control devices (i.e. welder, variac, chokes etc.)
> would have on the secondary's inductance. Upon further investigation, it
> looks like there would be absolutely no affect on the Xl of the secondary
> since these devices control the current before it reaches the primary.

Wrong. Whatever choke you stick on one side of an ideal transformer 
appears on the other with its value modified by the turns ratio. It 
should be remembered that while chokes are at first glance the most 
innocuous of current limiting devices, they do that with an expense:
they store energy in order to do so efficiently (c.f. a resistance =
Xl which doesn't and wastes a lot of power). You must model the 
situation as the primary cap Xc at mains frequency (or break 
frequency) plus Xl of the choke at whichever frequency is relevant.
Just as you use Xc=Xl in the NST situation, you must use the same
consideration for any system using an ideal transformer and 
"limiting" choke. This is the essence of efficient resonant charging.

    Re Ed's problem, it is apparent that he is experiencing this 
phenomenon. There is no other way you can charge the primary cap to 
beyond the o/c output voltage of the power transformer. The choice of 
break rate should take account of this.

Malcolm