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Re: Musein' and mathin'

Subject: 
        Re: Musein' and mathin'
  Date: 
        Mon, 17 Mar 1997 18:59:51 -0500 (EST)
  From: 
        richard hull <rhull-at-richmond.infi-dot-net>
    To: 
        Tesla List <tesla-at-pupman-dot-com>


At 09:20 PM 3/16/97 -0600, you wrote:
>Subject: 
>           Re: Musein' and mathin'
>      Date: 
>           Sat, 15 Mar 1997 14:28:18 -0800
>      From: 
>           Greg Leyh <lod-at-pacbell-dot-net>
>        To: 
>           Tesla List <tesla-at-pupman-dot-com>
>References: 
>           1
>
>
>> Pspice, like anything else on the CPU, is not auto-erecting and talent is
>> still required to formulate a good model followed by the grueling input
>> machinations.
>> 
>> Richard Hull, TCBOR
>
>
>Richard,
>
>All too true. The use of PSPICE as the sole design tool in TC work
>without an 
>experimental background could lead to some very costly heartbreaks,
>indeed.  
>For the most part I use PSPICE as an accounting measure, in order to
>make sure
>preliminary component values are adequate, and to find gross design
>blunders.
>
>For instance, shortly after I had built my coil the RF choke on the DC
>line
>kept overheating; the first one (PVC) melted! The single-layer choke was
>wound
>on 20" of 4" dia PVC pipe, using #22 ga wire.  The RMS DC current was
>only 
>3.5A, and the Rchoke was 10 ohms -- about 100W of dissapation.  
>
>What's wrong with that?! 
>
>As it turns out, when I simulated the _entire_ primary circuit in PSPICE 
>I discovered that the RMS current in the choke was actually 14A instead
>of 3.5A, 
>due to a large unforseen oscillation between Cpri and components of the
>filter 
>network.  That oscillation circuit path was then "de-Qed" using a diode
>and a 
>resistor, first in PSPICE and then in the actual circuit.  The choke
>runs
>only slightly above ambient temp. now.
>
>IMO, theory is much more accurate at predicting failure than success. 
>Virtually
>all designs that are theoretically impossible will ultimately fail, so I
>find
>PSPICE more useful as a litmus test for new circuit designs. 
>
>-GL
>
>Excellent post Greg, and the best I've seen on the benefits and pitfalls of
Pspice and such programs!

The ingredients for good results with anything are 1. informed user.
 2. experienced experimenter  3. Sound theoretical background  4.
debugging
skills  5. artistitc temperment to try and see the bigger picture in
motion
prior to making too many assumptions.

The De Q'ing of the choke is a nice touch and a fine example of thinking
on
the fly.

Richard Hull, TCBOR