Re: Differential triggered gap

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

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
> 
> 
> 
> 
>