Re: Differential triggered gap

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

Original poster: "Daniel Barrett by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dbarrett1-at-austin.rr-dot-com>

    Hi Robert!
    Thanks for the response. I probably should have mentioned that I have
capacitors before the choke as well. I put these in after the first couple
of diode arrays fried ;). They are not as big as I'd like, but 'parts are on
order'. They do a reasonable job of killing the worst of the transients *so
far*

(per side)                    9mH
--------------D|--------^^^^^-----------|
                           |                            _ 1/2 of MMC (90nF)
                           -                            _
                           -  .002 / 20kV      |
                           |                            |
-----GND-------------------------------

 -circuit is mirrored below ground for negative rail.


    But a smaller choke would have less of a trisient supressing effect,
wouldn't it?
I'm finding that my rectifiers were dying not of overcurrent but from high
dv/dt on their cathodes when reverse-biased. We really need fast-recovery
rectifiers here...
db



----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, August 10, 2002 9:13 PM
Subject: Re: Differential triggered gap


> Original poster: "rheidlebaugh by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<rheidlebaugh-at-zialink-dot-com>
>
> Daniel: Having used DC to power and charge the spark I see you used an 18
mh
> choke. I found I lost rectifiers due to surge current at the time the SG
> fires. If the choke is not fast enough to stop that surge your diodes will
> smoke. I used a much smaller choke. 15T 1" od 8" long of #12 wire  air
core
> coil in series with my DC supply powered with a 15/60 nst&rectifier. After
2
> years of use I lost no diodes due to surge. The coil must be fast.
>    Robert  H
>
> > From: "Tesla list" <tesla-at-pupman-dot-com>
> > Date: Sat, 10 Aug 2002 06:46:50 -0600
> > To: tesla-at-pupman-dot-com
> > Subject: Differential triggered gap
> > Resent-From: tesla-at-pupman-dot-com
> > Resent-Date: Sat, 10 Aug 2002 07:02:39 -0600
> >
> > Original poster: "Daniel Barrett by way of Terry Fritz
<twftesla-at-qwest-dot-net>"
> > <dbarrett1-at-austin.rr-dot-com>
> >
> > Hi List!
> > I have been trying to bring up an 8 inch by 36 inch DC powered coil
> > designed around a dual-MOT power supply and triggered gap and have had
> > limited success. I have an idea about the spark gap and wanted some
feedback
> > from some of you gurus ;)
> > About the design:
> > Secondary is resonant at 140kHz with topload.
> > The gap trigger is a microcontroller driving the usual
> > capacitive-discharge ignition coil circuit. I'm running this thing at
about
> > 5 BPS until I can convince myself that the power supply won't crater. I
have
> > burned through about 250 1N4007's this week :)
> > The power supply is 2 MOTs, one modified to float the ground connection.
> > These drive seperate pos and neg doublers, with approx +/- 10kV out. My
tank
> > cap is a center-tapped 45nF geek-cap array (3 string of 5 per leg). This
is
> > charged through a couple of 18mH inductors. Since the power supply is
> > bipolar, it seems to make sense to me to keep the primary circuit as
> > symmetrical and bipolar as possible. Because the power supply is
reasonably
> > well decoupled from the tank via theses charging inductors, Im
connecting
> > the gap as follows:
> >
> > GAP
> > +10kvdc-------[18mH]----------O O-----------
> > |               ^                   |
> > -               |                   |
> > 90nF         trig               |
> > -                                  >
> > |                                  >
> > Tesla coil
> > power_gnd----------------                                  > Primary
> > |                                  >
> > -                                 >
> > 90nF                             |
> > -                                 |
> > |                                  |
> > -10kvdc-------[18mH]--------------------------
> >
> > Gee. Someone needs to write an ORCAD-to-ASCII schematic converter ;)
> >
> > Ok, this works, but I'm having a lot of trouble finding a gap spacing
> > that (a) fires reliably on each trigger, and (b) doesn't power arc or
fire
> > muliple times per trigger. This is proving to be difficult. So now for
the
> > question: Would it be advantageous to build a tripple-gap as described
> > below? The idea is that the center gap fires (via the trigger circuit),
> > which raises the potential of the entire primary coil to
+some_high_voltage,
> > which should cause the bottom gap to over-volt and fire, pulling the
primary
> > to -10kv, which overvolts the top gap. Now the main discharge happens.
> > That's my theory anyway.
> >
> > GAP #1
> > +10kvdc-------[18mH]----------O O-----------
> > |                                  |
> > -                                 |
> > 90nF                           |
> > -
> >> TC primary
> > |                                  >
> > power_gnd----------------                                  > ------O
> > O--[igncoil]
> > |                                  >
> > GAP #3
> > -                                 >
> > 90nF                             |
> > -                                 |
> > |             GAP #2        |
> > -10kvdc-------[18mH]-----------O O----------
> >
> > Does this sound reasonable? Would this help increase the margin between
> > reliable firing and spontaneous firing? Any comments?
> > Thanks!
> > db
> >
> >
> >
> >
> >
>
>
>