RSG Idea, PSU Question

From:  Marco Denicolai [SMTP:marco-at-vistacom.fi]
Sent:  Thursday, July 02, 1998 12:57 AM
To:  Tesla List
Subject:  Re: RSG Idea, PSU Question

At 23:06 01/07/98 -0500, you wrote:
>-----Original Message-----
>From: Ian Hopley <i_hopley-at-wintermute.co.uk>
>To: 'Tesla List' <tesla-at-pupman-dot-com>
>Date: Wednesday, July 01, 1998 7:59 PM
>Subject: RSG Idea, PSU Question
>Hi all,
>Been away from the hobby for a couple of years, family raising and all
>that, and although not coiling again yet I thought I'd catch up with the
>latest ideas. One of my problems when I last fired was that I popped the
>last of my transformers (unpotted NST's and oil ignitor's), and was
>contemplating using MOT's as the former are very rare beasts indeed. The
>problem I found was the risk of secondary-primary flashover if more than
>two secondarys were connected in series. Then I spotted in somebodys post
>that they were using a voltage doubler arrangement. I understand the theory
>behind the doubler and it would certainly solve a lot of problems, but it
>raises a couple of questions:-

I guess you refer to my tank design: here follows the schematics (without RF
and the measurements I made.
I had eventually a chance of performing a real measurement on the circuit
below. I used a digital scope and applied to the mains 3.5 VAC instead
of 220 VAC. After the measurements, I scaled up the results and these 
I am reporting in the following.

                         | |    
       --------|| ||-----| |----*---------- V-
             * || || *   | |    |
               || ||          -----
   220V        || ||          \   /
               || ||           \ /
               || ||          -----
               || ||            |
       --------|| ||------------*--- GND
       --------|| ||------------*
             * || || *          |
               || ||          -----
               || ||          \   /
    220V       || ||           \ /
               || ||          -----
               || ||     | |    |
       --------|| ||-----| |----*----------- V+
                         | |    

Voltage V+ to GND oscillates between 6270 V and 0 (2200 VAC * 2 * sqrt(2) =
6270 Vpp). 
Voltage between V- and GND oscillates between -6270 V and 0.
If the transformers are in phase, voltage between V+ and V- is almost DC at
6270 VDC.

  V+ |----|    |----|    |----|
     |    |----|    |----|    |
 GND ------------------------------     V+ - V- = 6.3kV DC
     |----|    |----|    |----|
  V- |    |----|    |----|    |----
If the transformers are NOT in phase, the output is a sinusoid at 50 Hz
going from 0
to 6270 Vpp * 2 = 12540 Vpp.

  V+ |----|    |----|    |----|
     |    |----|    |----|    |----
 GND ------------------------------     V+ - V- = 0 to 12.5kV DC pulsed
     |    |----|    |----|    |----
  V- |----|    |----|    |----|

I use the last configuration (transformers NOT in phase, 12.5kV pulsed output).

>1) Was this arrangement used with a spark gap or solid state switched

I use a RQ spark gap.

>2) What sort of current/ power o/p  was available?

Depends on the MOT you are using. I use two 900W MOTs plus a third one
connected as
shunt (with its secondary shorted) on the 220V side.

>3) The voltage doubler arrangement gives a DC o/p and not much had been
>documented about the use of DC, will this require the use of a RSG as I was
>having very good results with an air quenched multi-gap powered by a vacume
>cleaner blower (sucker?).

As you can read above, with this design you can get either AC or DC, as you

>4) Any sugested values for doubler Cap's and Diodes?

Caps straight from a microwave oven are OK. Never blown one. Diodes from a
oven are OK too, if you use a shunt like me and don't get strikes from toroid to
primary. After several hours of happy Tesla lightning I got one of those strikes
that killed one of the diodes. I am going to test in the next days with a series
of two microwave oven diodes, with resistive divider network to split
correctly the
voltage on them and 750 pF capacitors in parallel for protection. I will
also employ
a strike rail.
I have also got a double 3mH inductor and 550 pF RF filter on both wires
going to the
spark gap and primary capacitor.
Diodes and capacitors have otherwise performed very well. And I never got
arcing or
faults on the MOTs. MO diodes are typically 9KV 450 mA.

At today, with this MOT tank and a 4" secondary I can easily get 20"
streamers to a
grounded point.


 Marco Denicolai                   Vista Communication Instruments, Inc.
 Hardware Development Manager      www.vistacom.fi   

 marco-at-vistacom.fi                 Kaisaniemenkatu 13 A
 fax:    +358-9-622-5610           SF-00100 HELSINKI
 phone:  +358-9-622-623-15         Finland

   Remember, Murphy was an optimist! I am not...