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Progress on the DC drive


From: 	L.Robertson[SMTP:LWRobertson-at-email.msn-dot-com]
Sent: 	Saturday, January 10, 1998 12:39 AM
To: 	Tesla Builders
Subject: 	Progress on the DC drive

Hi folks ...

I see some discussion lately concerning DC drive for coils,
and thought my struggles with such a drive may be of interest.

My last post was several thousand messages ago in October,
so I'll start with a short description of the basic system.

Power source    2 NST's  15 kV -at- 60 ma each.
Secondary        8" dia. plexiglas tube w/ 1050 turns #22 wire.
Primary            1/2 " copper tube, 16 turns semi-flat spiral 
                          1/4" separation, raised 2 " for clearance.
Top Load        One of 18" x 4" home made torus, or 30" x 8"
                         commercial torus.

As a classic coil it worked fairly well, producing around 36 "
of connected spark, and maybe 40 " of streamers using
a crude static gap consisting of 6 - 3/4" copper pipe
pieces 3 " long with a fan under.

I got a 2 uf 60 kV Aerovox pulse cap. for the storage
capacitor, and constructed a diode bridge from 30 kV
1 amp diodes, carefully placed in a tupperware full
of oil, and added quite alot of filters between the diodes
and the Aerovox.

My rotary gap was initially designed as a push-pull circuit
swapping the 0.018 resonance cap polarity on each gap
presentation.

This resulted in about 12 " sparks, but the safety gap on
the capacitor started barking at only 25% on the variac.,
even when opened to 1" .

O'scope indicated huge 5 Mhz parasitic oscillations.

Thinking something was sadly amiss, I removed the diodes,
left the filters in, and one side of the Aerovox connected, and
used the static gap - getting 40" of connected spark, thus
proving at least my resonance cap was good.

I then reconnected diodes and used the Aerovox as a filter
across the output, used a 50K resistor between it and the 
classical tesla circuit - still using the static gap - and got
kind of a multispark effect - the gap would discharge about
8 times at a 400 Hz rep rate, then wait for a few tenths of 
a second, then repeat. The gap was quenching right at the
top of the first primary ringup, and the sparks looked more
like the discharge from a pulse transformer, being hot and
white but not very long.

When I substituted the rotary, it would multispark at each
gap presentation, but my gap configuration was not set 
up for a fast rep rate.

I have just now reconfigured the rotary to give up to 700
PPS, and will see what happens when the break rate
equals the "natural"  respark rate.

LR