Re: Triggered gap and safety gaps

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

Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bert.hickman-at-aquila-dot-net>

Richard and all,

I don't think that kickbacks will be a problem as long as you use
relatively small (500 pF) doorknob caps in series with the trigger and
return to the trigger coil to serve as blocking caps. The worst case
kickback that can couple back into the secondary side of the trigger
circuit will be of the order of .05 Joules since it will be "limited" by
the charging of the doorknob caps. A failure of a blocking cap could cause
the tank circuit to back up into the secondary of the trigger coil, but as
long as the "low" end of the coil was grounded, even this should not create
a significant problem - the turns ratio of the trigger coil will reduce the
amplitude on the primary side as Richard indicates. Safer trigger phase
adjustment "on the fly" can be done by simply making a suitable extension
of the plastic knob from a drilled out plastic rod or even a chunk of heat
shrink tubing slipped over the knob of the pot of the dimmer. Finally,
using MOV's on the mains side to ground should suppress any abnormal
nasties from getting back into the mains... 

Best regards,

-- Bert --
-- 
Bert Hickman
Stoneridge Engineering
Email:    bert.hickman-at-aquila-dot-net
Web Site: http://www.teslamania-dot-com

Tesla list wrote:
> 
> Original poster: "Richard Wayne Wall by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <rwall-at-ix-dot-netcom-dot-com>
> 
> I think Dave Sharpe's optical isolator scheme will be ultimately the safest
> solution not only for the triggered gaps, but also for a wide variety of
other
> future variables we may eventually wish to change on TCs "on the fly".  I
look
> forward to his input.
> 
> Having said all that, I have a few observations.  Since an automobile spark
> coil is simply an auto transformer, if there was to be a 5-10 J HV kick
back of
> say 12 KV pulse, then the voltage differential across the two inputs
should be
> way lower.  Maybe  ~120 volt pulse which is presented to the triac -- just by
> transformer action of the auto transformer.  (These numbers are not accurate
> and are for illustration only.)  If the grounded terminal is connected
closest
> to the HV winding on the auto transformer, the HV pulse would be most likely
> shunted to ground.  Also 140 volt MOV's could be place on he low voltage side
> before and after the triac.
> 
> Any thoughts?  Bert, Jim, Terry, list?
> 
> RWW
> >
> >
> >
> > Original poster: "David Sharpe by way of Terry Fritz
> > <<mailto:twftesla-at-qwest-dot-net>twftesla-at-qwest-dot-net>"
> > <<mailto:sccr4us-at-erols-dot-com>sccr4us-at-erols-dot-com>
> >
> > Terry, Ted, ALL
> >
> > I think in lieu of the following posting, that the SCR - Variac controller
> > I was
> > posting a while back should be made available as a triggered gap
controller.
> > The advantage is the unit can be optically isolated.  I much prefer that
> > approach
> > to turning a knob that might have a 5-10J impulse coming back into the
> > ignition coil.  Bert Hickman posted awhile back about using a 500 pf
> > (there-about)
> > 30-50kV cap between trigger electrode and ignition coil to isolate from
main
> > gap pulse.  The control circuit would be nothing more then a variable
> > illumination
> > on a CdS photo resistive element is series with back to back SCR's.
> > Isolation
> > could be accomplished with a fiber optic at that rate.  Ted's comment
is well
> > founded, we should avoid adjusting running coils, especially on the HV side
> > while the system is running.  One mistake could be someone's last.  Let me
> > make several corrections, and I'll post the EDN circuit via Terry.
> >
> > Regards
> > Dave Sharpe, TCBOR
> > Chesterfield, VA. USA
> >
> > Tesla list wrote:
> >
> > > Original poster: "Ted Rosenberg by way of Terry Fritz
> > <<mailto:twftesla-at-qwest-dot-net>twftesla-at-qwest-dot-net>"
> > >
> > > Mike:
> > > I am close to the point of setting one up. Waiting on a part from
McMaster.
> > > I plan to have the dimmer in a standard AC box and connected by a
line cord
> > > to the cap and ignition coil (a remote config). However, I can assure you
> > of
> > > one thing: I will NOT attempt any adjustment of the dimmer/T-Gap while
> > > anything is powered. Period. Ain't worth it!
> > >
> > > Safety First...Really!
> > >
> > > Ted
> > >
> > > Subject: Re: Triggered gap and safety gaps
> > >
> > > Original poster: "by way of Terry Fritz
> > <<mailto:twftesla-at-qwest-dot-net>twftesla-at-qwest-dot-net>"
> > > <<mailto:CHURCHMON-at-aol-dot-com>CHURCHMON-at-aol-dot-com>
> > >
> > > Hi Johnathon and list ,
> > > I too am concerned that if I build one of these triggered gaps that I
could
> > > get back
> > > lash from the tank circuit if I come in contact with the dimmer knob.
> > > Has any one else experienced any from these type of trigger circuits ?
> > >
> > > Thanks ,
> > > Mike Church(CHURCHMON)-at-aol
> >
> >
> >
> 
> 
> --- Richard Wayne Wall
> --- <mailto:rwall-at-ix-dot-netcom-dot-com>rwall-at-ix-dot-netcom-dot-com
> 
>