RE: SSTC battle continues!

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

Original poster: "David Trimmell" <humanb-at-chaoticuniverse-dot-com> 

I agree that this is all vary good practice Steve, but if your driver
has proper RF by passing and a solid single point RF ground that avoids
"ground loops" then really there is no need to go into the HFRF style
shielding hassles. I have run my protoboard driver within a foot of my
6" coil with out any issues, but I must note that I am only getting 27"
max sparks out of my half-bridge (190VDC). Even so, proto boards are not
great in RF service, but work well enough. I am looking forward to
trying Dan's new driver board and finally making a full-bridge.

Regards,

David Trimmell

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Friday, August 13, 2004 11:04 AM
To: tesla-at-pupman-dot-com
Subject: RE: SSTC battle continues!

Original poster: "Steve Conner" <steve.conner-at-optosci-dot-com>

  >He's talking about battles with the driver

Yes, it can be a battle just getting a SSTC to work and stay working for
more than 10 seconds. All those problems multiply as the coil gets
bigger
and more powerful.

But knowledge of practical EE matters like layout, shielding and
grounding
can help you a lot. These are far more important than they were in
spark-gap
coiling- it takes a lot less interference to destabilise a self-resonant
controller than to burn out an NST :(

In practice, it's probably a good idea to build your SSTC controller,
and
plan the wires that connect it to power supplies, H-bridge, ground etc,
with
the same attention to shielding and grounding as a computer CPU box or a
high-sensitivity radio receiver. Radio techniques are quite appropriate,
as
the idea in a driver is to let the power supply and feedback signal into
the
box, and let the gate drive out, while keeping all other
conducted/radiated
interference out.

Possibly the worst offender is ground loops that include your SSTC
driver
circuit board. These can pick up magnetic field from the
primary/secondary
coils as well as the large dI/dt caused by an arc to ground.

Another bad source of interference is the dV/dt caused by an arc to
ground-
as the toroid capacitance is suddenly discharged to ground, it pulls the
local RF ground up to a remarkably high voltage. This effect is
discussed in
textbooks on commercial lightning protection. It can cause electrostatic
coupling of hash into your control circuits, and even cause the RF
"ground"
to arc over to your control circuits which are hooked to a different (AC
line) ground.


Steve C.

best SSTC spark so far: 185cm

Death toll: 9 small IGBTs, 2 fast recovery diodes, 4 MOSFETs, 6 UCC3732x
driver chips, a pile of 555/74HCxx/LM339/2N3904/etc, a heap of fuses,
and
one 240V 40W filament bulb burnt out by ground strike current.