Re: bi-polar (center-fed) TC

• To: tesla-at-pupman-dot-com
• Subject: Re: bi-polar (center-fed) TC
• From: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
• Date: Fri, 07 May 1999 01:28:20 -0600
• Approved: twftesla-at-uswest-dot-net
• Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

> Original Poster: Parpp807-at-aol-dot-com 
> 
> In a message dated 5/2/99 6:31:48 AM US Eastern Standard Time, 
> tesla-at-pupman-dot-com writes:
> 
> <<original Poster: "Thomas McGahee" <tom_mcgahee-at-sigmais-dot-com> 
>  
>  One problem that most experimenters building bipolar center-fed
>  Tesla coils fail to take into consideration is the difficulty of
>  adjusting the coupling. If you simply slide the primary more
>  towards one side, you increase the coupling on one side and 
>  decrease it on the other side.
>  
>  If the experimenter fails to ground the secondary at its center,
>  then approaching either of the ends will cause the voltage on the
>  other end to change drastically. Quite often the circuit will
>  respond by causing sparks to fly between the primary and the 
>  secondary at or near the center.
>  
>  For these reasons it is generally better to make a bipolar
>  Tesla coil that uses two distinct secondaries having the bases
>  both tied to a really good common FR ground. Such a bipolar
>  Tesla coil will have separate primaries for each secondary.
>  The coupling of each can be independently adjusted. 
>  
>  The primaries
>  have to be properly phased so that the tops of the two secondariness
>  are out of phase. You can wind the secondariness in the same direction
>  and the primaries in the same direction, and achieve proper
>  phasing by just phasing the *connection* to the primary. There
>  is NO need to wind any of the coils differently (although that is
>  just as valid a method to achieve proper phasing).
>  
>  Hope this helps.
>  Fr. Tom McGahee 
>  
>   >>
> Tom,
> That is an interesting design for a di-pole TC, it's one that I have not 
> previously seen.
> The center-tapped secondary will always have ends 180 degrees out-of-phase. 
> Same
> for the two primaries which I guess are connected in series. From your 
> experiments,
> just how critical is an accurate determination of the "electrical center 
> line?" This design will also require a mechanical means for the lateral 
> adjustment of the two primary
> windings. 
> 
> Ralph Zekelman

You can create a bipolar coil by using two secondaries and a single 
primary, the arrangement being that one of the secondaries is coupled 
to the primary and the other secondary is free-standing and connected 
to the base of the driven secondary rather than the base of the 
driven secondary being connected to ground. The only catch is that 
there is an imbalance in the system which can cause arcing between 
the primary and its coupled secondary under some loading conditions.
The ideal setup would be to have the secondaries both free standing 
with a close coupled driver a la:


       SSSSS                SSSSS
       SSSSS                SSSSS
       SSSSS                SSSSS
       SSSSS____DDDDDDD_____SSSSS
                 PPPPP

where SSSSS are the free standing secondaries, DDD is the drive 
secondary having a centre tapped connection to ground and PPP is its 
primary.

Malcolm

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