Equdrive circuit, was Re: SGTC

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: FIFTYGUY@xxxxxxx 

In a message dated 4/28/07 6:48:25 P.M. Eastern Daylight Time, 
tesla@xxxxxxxxxx writes:

>As long as the gap is parallel to the transformer, I can't see a
>charge remaining. But, what if the gap was hooked in series on one or
>even both legs (between caps and primary)? Then as the last cap
>conducted at turn off, the opposite cap would remain with a charge.
>In that situation, it is likely there would always be one of the caps
>charged (and you would never really know which one). That type of
>circuit would require an external bleeder for safety.

    Why would one cap "conduct" (discharge?) without the current 
going through the other one as well? Maybe in a very odd 
center-tapped primary configuration. But then you'd essentially need 
a complete duplicate of each primary coil, cap, and spark gap, with 
the only advantage of a 50% drop in duty cycle on the components. 
Maybe it's worth it?

>This must have been the circuit where statements of remaining charge
>are referred to.

        Richard Hull's "The Tesla Coil Builder's Guide to the 
Colorado Spring Notes of Nikola Tesla" clearly shows a diagram of a 
single gap (combination series/rotary) across the transformer, along 
with two caps in "Equi-Drive" configuration. On this page (pg. 15) is 
where Hull most strongly advocates the "Equidrive". In fact, he writes:

    "We have dubbed this the 'Tesla Equidrive Tank Circuit'. It 
allows for greatly increased break rate over most other circuits. The 
only disadvantage to the casual Tesla coil builder in using this 
circuit is the requirement for a number of exactly matched 
capacitors. There is a major caveat to be concerned with when using 
the above balanced circuit. Upon powering down, the capacitors will 
most likely retain a LETHAL charge! YOU MUST PERSONALLY DISCHARGE THE 
CAPACITORS IMMEDIATELY UPON SYSTEM SHUT DOWN! This takes on a new 
meaning for the active experimenter who is likely to retune his 
system immediately after firing. DO NOT GRAB THE PRIMARY TAP UNTIL 
YOU HAVE SHORTED OUT BOTH CAPACITORS! The use of a regulating coil 
will obviate this somewhat but the deadly charge on the capacitors 
will still be there!"

    So, to reference the original post, Hull is referring to a "Case 
3" circuit. He also indicates that *both* caps in an Equidrive 
configuration can retain a charge, and this danger is greater than 
using a single cap. He also expresses in numerous other places the 
importance of perfectly matched caps when using an "Equidrive". And, 
of course, he writes that there are advantages that the "Equidrive" 
can obtain.
    None of this makes any sense to me!

    FWIW, Hull's diagram shows a "regulating coil" (what we on the 
current TCML would refer to as something like an "off-axis primary 
tuning inductance"). This was apparently a usual tool of Tesla's, and 
Hull shows it in the diagram and describes it (after all, these are 
his guide to Tesla's notes). Hull of course mentions in several 
places that this "regulating coil" could be done away with, but that 
it can be a "great experimental tool, but can be misused if too much 
inductance is used in it".
    The interesting thing is that this "regulating coil" is shown in 
the "Equidrive" schematic in one leg only! After all the (mystical?) 
effort Hull describes Tesla expended to keep the circuit perfectly 
symmetrical, the tuning coil is a large and intentional *asymmetry*. 
Even then, I can't see why the "regulating coil" could possibly 
effect retained charge or give an advantage to the "Equidrive".

-Phil LaBudde




----------
See what's free at <http://www.aol.com?ncid=AOLAOF00020000000503>AOL.com.