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DC Tesla Design Information, Schematics and Photographs
There have been a number of questions about DC driven Tesla coil
designs lately. I was able to run my early design at the '99
SoCal Teslathon (kindly hosted by Brian Basura).
Among the many great pictures were a few of the setup,
although none running. There is also a full schematic and fairly
well detailed design information on the SoCal page along with the
pictures I supplied.
For pictures and schematics of my earlier version of a DC-driven
Tesla design take a look here:
http://fp2.hughes-dot-net/brianb/kevin.htm
There are some additional pics on my ftp site here:
ftp://ftp.mindspring-dot-com/users/ottalini/highvoltage/6inch/
And other pictures and information:
ftp://ftp.mindspring-dot-com/users/ottalini/highvoltage
or if that doesn't work, try linking to the ftp through the website:
http://www.mindspring-dot-com/~ottalini
I finally rebuilt my primary and changed the power supply to a 15kv,
1.5kw, single stage full-wave rectifier design (for now). After
doing a bit of R&D, I was forced to realize that the total power
input _is_ just as important as the input voltage, especially from
a recharge rate (of the main capacitor banks) point of view.
Lets see, the faster the rotary gap, the faster the recharge rate
needs to be. The faster the rep rate, the easier it is to overcome
the many misc. losses to achieve breakout. It takes more time to
charge up to a higher voltage, but the losses increase as well.
Hmmm, it is easy to lose the big picture when faced with a lot
of little fixups. Where, oh where is that mythical "sweetspot"?
Even so, the effects of a faster rep rate at a lower voltage are
quite interesting with this DC architecture, both visually and
acoustically. I spent some time creating a functional graph
of primary capacitance VS primary turns and have been studying
the overall performance differences at each peak.
ftp://ftp.mindspring-dot-com/users/ottalini/highvoltage/information/prime1.pdf
I was using a 20KV (30kv max), 780watt max supply before with
a 3*0.125ufd cap (.042uFd) arrangement (at the Teslathon).
With the new setup, I'm using a 1.5kw (2kw peak) 15kv max transformer
and a 4-cap (~.03uF) storage bank. It takes about 5ms to recharge
and about 200us to discharge the bank with a total power of 1400watts
to run at 100bps. The secondary appears to be oscillating at about
11us at the moment (90kHz). I also have a small variac now to run
the rotary gap motor ... a big improvement over the batteries.
At about 200bps, I'm competing so closely with the recharge
rate and the total power available that the supply is unable
to keep up, but the overall performance just shy of that is
quite amazing if not a little frightening. I know my neighbors
got quite interested after just a few minutes of operation.
By increasing the primary turns and decreasing the capacitance,
I should be able to decrease the recharge time (and instantaneous
power) and thereby improve the overall rate performance, or
in trade, increase the input voltage and try to take advantage
of the CV2 performance curve (my original intent).
Since the coupling is very high, there should be only a minor
performance loss as L increases and C decreases (total field
volume). Certainly the load on the rotary gap is easier with
a lower C as well.
It is also nice that the DC drive design eliminates virtually all
the many sync and safety gap problems that seem to plague the
majority of typical AC designs.
I also am updating the rotary gap to an 8-pole design using
stainless dowel pins. I'll provide additional information on dowel
pin size, count, dwell time, discharge rate and recharge time as
I get time.
*---------------------------*
* Kevin Ottalini *
* WhoSys / Who Systems *
* High Voltage with Style! *
* ottalini-at-mindspring-dot-com *
* Often in Another Reality *
*---------------------------*