Re: DRSSTC Primary Circuit Feedback Control

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Steve Ward <steve.ward@xxxxxxxxx>

Hey Terry,

I tested primary current feedback quite a ways back with my first
DRSSTC.  It still made about 48" sparks from about 1000W input power,
good performance.  Interestingly, secondary feedback gives a nice
linear looking ringup while primary feedback is almost a "stepped"
ring up, probably the phase relationship between the 2 LCs causing
that effect.  Anyway, both ways seemed to work well, and ive even been
considering using primary feedback on my larger DRSSTC, but that might
not happen for awhile.  Anyway, im certain that you would have to
build in an overcurrent detection circuit on the primary side in this
situation to prevent things from running away.  I use overcurrent
detection on my big coil and it triggers on every ground strike ;-)
and also knocks off about 3 RF cycles!  Whats interesting is that it
can still feed the ground arcs, yet my controller is hacking off like
20% of the bang :-).

Cant wait to build the CM600 coil :-))

Steve


On Mon, 06 Dec 2004 21:09:37 -0700, Tesla list <tesla@xxxxxxxxxx> wrote:
> Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>
>
> Hi Jimmy,
>
>
>
> At 08:50 PM 12/6/2004, you wrote:
> >Hi Terry,
> >
> >The little IGBTs should be practical anyway. Based on some
> >measurements taken on my DRSSTC, I'm convinced that a half bridge of
> >little TO-247 IGBTs could get me to 5'.
> >
> >You have to be a little careful with primary feedback, because if it
> >isn't tuned, the secondary won't be sucking much out, and it will
> >build up more than normal
>
> Yes!!  The models show that for sure.  If the primary and secondary are not
> tuned, then the primary voltage just keeps rising pretty much till
> something blows up!!  A spark gap might "still" be a good idea ;-))
>
> The models (not real confident in the numbers..) say the IGBTs will do
> about 40 watts of heat as is.  But with "perfect" zero cross switching,
> that goes down to 1.2 watts!!  This is no different than any other
> switching resonant thing and they are all using "little" FETS and
> IGBTs...  We just have to refine ours...  I also seem to be able to keep
> the peak primary currents at just 80 amps which is trivial for the
> IGBTs.  Almost could use FETs again...
>
> Cheers,
>
>         Terry
>
>