SSgap Update 4-1-2001

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

Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

Hi All,

I have cleaned up the schematics of my solid state gap project and posted
them along with a few pictures of the test setups at:

http://hot-streamer-dot-com/TeslaCoils/MyCoils/SolidStateCoil/SSgap2001-4-1/

The controller is just a bunch of CMOS 555 timers and HCT logic chips.
Signals are pulled off the NST and high voltage rectifier to signal Sync
and Static gap timing.  The optical sender has been improved to provide
solid fast signals to the modules.  The power blocks are basically the same
but the control electronics are now IR-2118 driver chips with 5 volt logic
available.  That allows simpler designs in the future probably without the
controller needed.  Everything is run off batteries.

The fiber optic senders are now down to about 100nS... Hey! gota have it
;-))  I have faster receivers on order from two venders.  The IF-D95T seems
to have random propagation delay from 2-6 mS which is a BIG problem.  The
IF-D96 should reduce that to 65nS :-)  Turn off is also pretty messy on the
D95T.  It is important to have solid, clean, and fast signals on something
like this...  The IR-2118 drivers provide good solid signals to the IGBTs
and I added a 100 ohm resistor per Marco's suggestion now that the drive is
so powerful.  I still use the D95T for some signaling since it is very nice
if super fast stuff is not needed.  

The control electronics can easily do a current limit function but I have
not found a good way to implement that.  I need to quickly light an LED
(5uS) when the current reaches 500 amps in a ~250kHz signal.  I am trying
to get yet another Pearson 4100 current monitor (ya never can have too many
current monitors ;-)) but that is not the best solution...  Each IGBT can
"eat" 20000 watts max instantaneous power.  That comes out to a hefty 1.5
Megawatts for the array.  However, if an 8 joule primary cap unloads in
5uS, you are right there at 1.6MW instantaneous power...  It is interesting
to consider that if the primary cap is low loss (MMC) and the gap is low
loss (solid state) and you don't have a secondary, where does the power
go??  I fear it will be something destructive.  Probably the IGBT silicon
will have to be the energy dump...  A little more messy that just a "really
bright" spark at the rotary gap...  Perhaps a very small spark gap added to
a solid state gap could provide a place to dump energy when needed...
Another option is just "not to fire" and let the safety gaps or MOVs eat
the energy...  Much to think on there...

I am now down to ordering parts "next day".  I have next week off from work
(forced shutdown :-)) so I plan on really cranking on this thing.  I need
to get my little PC board shop back on-line (need to get new PCB software
for Win2K (grrrr)) since this will need a lot of repetitive PC boards.
Today was like 75 degrees Fahrenheit right into the evening so I cleaned up
the outdoor shop (not a small task!!) and fixed up the tools (replaced 4
power cords on Makita (can't make good power cords) tools (grrrr)).  I
built up a MOT supply for testing.  It was super nice having the shop warm
again and having the table saw, drill, press and other tools easily
available again after a long winter!!!

Once the MOT supply is all together I can pump some real current and
voltage through the test setup and see how it goes.  This is all still very
"on paper" at this point so who knows what "fun" lies ahead.  The R&D
budget is now at $1000 and I suspect the thing will run $2000 more to build
the full blown thing.  I will go in stages incase it all goes bad and I
have to bail out.  No one ever said this would be cheap gap ;-)) 

So, all is still going well and much excitement here!!

Cheers,

	Terry