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Re: bi-polar (center-fed) TC


----- Original Message -----
From: Tesla List <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Thursday, May 06, 1999 12:56 AM
Subject: Re: bi-polar (center-fed) TC


> 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


Hi Ralph
Let me put my 2 cents worth into the discussion. .If you look on page 92 of
a book called High Frequency Apparatus by Thomas Stanley Curtis copyright
1916 reprinted by Lindsey Publications you will find a picture and
construction details for this exact system. I've seen the same design
elsewhere. Seems there is nothing new under the sun. This type of system
doesn't have a lateral sliding primary like you mentioned although I see no
reason why it couldn't but it would be a bit difficult. Tesla employed a
sliding primary  which was not grounded to the center of the secondary on
his oil insulated bi-polar demonstration coils to balance whatever load he
wanted to connect to the terminals. What's wrong with one more adjustment on
a coil? I have found it useful for the same reason Tesla did, but there can
be an arcing problem. That's why I am experimenting with an oil insulated
version myself. My air insulated Bi-polars exhibit the problems Tom talks
about if I run my primary voltage too high. for the primary to sec. spacing.
The Bi-Polar Tesla Coils we use here at the picture tube plant are air
insulated and run without the primary grounded to the center of the
secondary. We have 200 coils in operation working 6 and 7 days a week 24
hours a day, we loose very few secondaries to arc overs. I'm not advocating
the use of either type but both have their strong and weak points.  the
ungrounded type is however the "classic" design. The other version will be
less troublesome and will probably give longer sparks if thats what you're
after. I'll have to try a grounded center one myself one day, maybe I won't
need all this messy oil.
Mike



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