Reflected Power

To: "'Tesla List'" <tesla-at-pupman-dot-com>
Subject: Reflected Power
From: Tesla List <tesla-at-stic-dot-net>
Date: Sat, 31 Jan 1998 10:12:58 -0600
Approved: tesla-at-stic-dot-net

----------
From:  John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
Sent:  Friday, January 30, 1998 7:30 PM
To:  Tesla List
Subject:  Re: Reflected Power


  All -

  The reflected power can be optained from a meter similar to what radio
hams use for radio transmitters. A graph showing the difference between
radio and Tesla coil reflected volts is shown in my Tesla Coil Notebook. The
graph shows the VSWR for radios and Tesla coils. Radios work best at low
VSWR and Tesla coils at high VSWR. Reflected power and voltages are
important to Tesla coils because they give an indication of how effective
the system is operating. 

  Also, the Q factor can be found by the VSWR obtained from the reflected
voltages as shown in the Notebook. To my knowledge, no coilers have ever
utilized this information in the design of Tesla coils. The Corum's have
mentioned VSWR for Tesla coils but gave no details.

  John Couture

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At 11:10 PM 1/29/98 -0600, you wrote:
>
>----------
>From:  Scott Stephens [SMTP:stephens-at-enteract-dot-com]
>Sent:  Thursday, January 29, 1998 11:56 AM
>To:  Tesla List
>Subject:  Re: Reflected Power
>
>At 11:54 PM 1/27/98 -0600, you wrote:
>
>>> >I'm in the process of rewinding the secondary of the output
>>> >transformer of my flyback converter. In an attempt to match the
>>> >impedence of the Tesla coil I'm adding more turns. Are there any ham
>>> >radio operators on the list that knows what reflected power looks
>>> like
>>> >on a O,scope? I've been seeing a strange waveform on the scope and I
>>> 
>>> Unfortunately there is no visual difference in reflected and real
>>> power.
>
>and
>
>>  Another question I would like to ask is when you increase the turns
>>ratio to increase voltage will this cause a coresponding increase in
>>current draw? My reasoning says it should but I would like to get some
>>feedback from someone with experiance.
>
>Yes, it will cause an increase in current.
>
>I've been troubled by the same problem lately. If I make my primary
>resonant, and try to operate at near maximum voltage, and don't dissipate
>all my power in my load, VSWR (the reflected wave) will add and destroy my
>transistors.
>
>But I have no load until a spark occurs. And after a spark, I have to charge
>up my coil again, resulting in a heavy load. So the requirement is realy for
>a variable primary.
>
>Solutions:
>
>Directional coupler and pulse-width/rate modulation. The directional coupler
>can redirect the reflected power into a dummy load. Otherwise my
>snubber/transorbs will die. The modulation can prevent overload of the
>transistors.
>
>
>