Re: MOT Powered SSTC - First Tests Successful!!

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>" <dhmccauley-at-spacecatlighting-dot-com>

 >  > To get big output on a SSTC, you need big voltage input.
 >
 > Dan I love your design, the high voltage definately seems to work and
 > all, but I absolutely disagree that using HV input (like from a MOT)
 > is the only route to huge arcs.
 >
 > Input POWER is what is needed, regardless of the input voltage or
 > current.
 >
 >  > But this design is flawed as it extremely limits the output of your
 >  > SSTC as input voltages are relatively low
 >
 > I don't think it's that limited at all...sure, impedance matching is
 > a little more difficult with low input voltage (4 turn primary vs. 20
 > turns), but 6 foot + arcs arcs are WELL within the capabilities of
 > the H-bridge topology for an SSTC.
 >
 > Recipe For Huge Arcs: 3 turn primary, 4" tall 6" O.D., 4" secondary
 > with #28, 240Vrms 1/2 wave DC input, and an H-bridge using 60+ amp
 > MOSFET's.

I wasn't saying that huge arcs are impossible with a full-bridge SSTC.  I
was trying to say it would be extremely difficult and a relatively complex
and expensive
device.  Perhaps when those 10kV FETs (single packages) come out in the next
decade or so, a simple full-bridge would be capable of 6 ft arcs rather
easily.
But at this time, it would be very difficult to get anything more than 24
inches from a 240VAC driven full-bridge SSTC.  Case and point is that with
all the full-bridge SSTCs already
out there, no-one has really exceeded 24" yet.  I've hit beyond that using
my full-bridge SSTC, but I was pushing almost 480VAC.  And that was before
catastrophic destructions of
all my FETs ! ! ! !  So I limit my SSTCs to 240VAC now.

As for power vs. voltage, I still think voltage is the decided factor for
"directly" driven SSTCs.  Perhaps with DRSSTCs, it would be different, or an
SSTC where there was an actual
primary tank circuit, but with a direct driven primary SSTC, voltage is
where its at!

On example regarding power input is the following experiments I've run:

HALF-RECTIFIED - NO CAP FILTER
HALF-RECTIFIED - SMALL CAP FILTER
HALF-RECTIFIED - LARGE CAP FILTER
HALF-RECTIFIED - VERY LARGE CAP BANK

Each of these tests were used with 240VAC input.  Peak voltage was constant
except at each step of increasing size capacitor bank, the input waveform
had decreasing ripple (with
capacitor filters) so that at the last step, the input voltage was about
equal to a DC value of the half-rectified peak voltage value.

Each step, power input was significantly higher than the previous step.

HOWEVER, even though the range of power was about 1kW to 3kW, output arc
length remained CONSTANT.  The arcs grew much thicker and nastier looking
but overall length
wasn't increased with increased power input.

In the next step, I would increase the input voltage a bit (using my
autotransformer variac), and the arc output grows nicely!

 > Again, even with spark gap TC's, it's input power that is necessary
 > for huge arcs. This is a very well known concept. For instance: a 7kV
 > 100mA coil can arc just as far as a 50kV 14mA coil. Same power (700W)
 > for both coils.

Yes, I do agree with you on that statement.  Basically because you are
charging up a primary tank circuit and discharging this energy into the
primary.
BUT, with a direct driven primary SSTC, there is no energy storing tank
circuit.  Again, perhaps with a DRSSTC this would be different, but I
haven't explored
that area yet.

 > To finalize my thoughts, I will add that my friend Aron Koscho's SSTC
 > achieved a measured sparklength of 32" (Dan, no offense to that extra
 > 2", it's just what it happened to be), using an H-bridge running off
 > of 240V. The reason it's not smeared across our website is because it
 > only lasted about 3 seconds due to using only 20A parts (IRFP460's -at-
 > 20A Id). Aron used a 4 turn primary wound 5" tall, coupled to a 4"
 > secondary wound with #28.

Sounds cool.  Has he made any progress to replace the FETs with higher
current ones?

In summary, my point wasn't meant to say large arcs are impossible with
full-bridge driven SSTCs, but that it can be fairly difficult as proven in
your friends Aron Koscho's design.
I'm merely saying by starting off with a higher input voltage for "direct
driven" SSTCs one can make life much more easier can obtain those longs arcs
much easier than working with
a lower voltage full-bridge circuit.


 > Regards,
 >
 > Justin Hays
 > KC5PNP
 > Email: justin-at-hvguy-dot-com
 > Website: www.hvguy-dot-com
 >
 >
 >
 >
 >