Re: "DC drive"

Tesla List wrote:
> >From lod-at-pacbell-dot-net Sun Dec  8 22:59:06 1996
> Date: Sun, 08 Dec 1996 15:26:31 -0800
> From: lod-at-pacbell-dot-net
> To: tesla-at-pupman-dot-com
> Subject: Re: "DC drive"
> DavidF wrote:
> > I have always been interested in a DC coil, would you tell me more about your
> > powersuply and gap and how the DC affects the design and performance of your
> > coil as compared to an AC neon garden variety?
>   My coil uses a 3-phase DC power supply followed by a resonant charger for
> providing the prime power to the primary circuit.  The PS consists of three
> oil-filled HV xfmrs (one per phase), followed by a 3-phase full wave
> rectifier set consisting of six rectifier stacks arranged in the standard way.
>   The resonant charger is a 2.5H, 10A, 28kV reactor in series with the output
> of the rectifier stack,  which gives the charging ckt a ringing frequency
> of about 150 Hz (Cpri = 0.495uF).  Cpri charges to twice the DC voltage in
> one half-cycle of the 150Hz, allowing gap speeds of up to 300 PPS.  The current
> pulse during charging is limited to Vdc/[sqrt[Lreact/Cpri]], so no other
> current-limiting chokes or resistors are required.  In fact, the LV windings
> of the xfmrs are directly connected to the 3-phase mains when power is applied--
> Either in the star configuration (by contactor A) for low power operation,
> or in the delta configuration (by contactor B) for full power operation.
>   A DC system is more complicated than a single-phase AC system, requiring
> HV diode stacks, polyphase xfmrs and switchgear, and charging reactors, but
> the DC method also offers a few advantages:
>   a)  The ability to use polyphase power, for better load balancing at higher
>       average power levels
>   b)  Improved power factor, due to resonant charging
>   c)  Rotary gap speed does not need to be synchronized to the mains, allowing
>       the gap speed to be variable for output power control
>   d)  Coil output voltage is more constant, since the primary charging voltage
>       does not cross thru zero twice each 60Hz cycle.  This improves the arc
>       length somewhat, due to the finite ion lifetimes in the output streamers.
>   I wonder what Tesla would think about powering one of his coils from DC?
> (remember War of the Currents?)  Perhaps it would be sufficent consolation as
> long as the DC part is powered by polyphase.
> -GL


Tesla has mentioned on several occasions that the best Tesla coil system 
would be powered by pure DC and even used DC generators (MG sets) in his 
Houston Street lab at times.

I have, in my possesion, diagrams and personal notes from Tesla which 
indicate that he was going to use polyphase AC, exclusively, timed by a 
form of rotary phase locked interrupt to give an effective, unfiltered DC 
to his Wardenclyffe tower system.  Some of this is intimated by Tesla to 
his lawyers in Anderson's work of 1993 on Teslas work with wireless 
transmission, telegraphy and teleponey.  Photos of the three large 
transformers for use in his polyphase Wardenclyffe system are shown. 

 Tesla was only for AC when it worked!  Mainly in power transmission and 
distribution schemes.  Who would have guessed that with modern methods, 
high tension DC power transmission would be given a re-birth in the late 
20th century?!!  Older, limited, or discredited concepts are often picked 
up and dusted off in the light of newer discoveries.

Richard Hull, TCBOR