Which DC Drive?

To: "'Tesla List'" <tesla-at-pupman-dot-com>
Subject: Which DC Drive?
From: Tesla List <tesla-at-stic-dot-net>
Date: Wed, 10 Jun 1998 19:48:00 -0500
Approved: tesla-at-stic-dot-net

----------
From:  Marco Denicolai [SMTP:marco-at-vistacom.fi]
Sent:  Wednesday, June 10, 1998 2:52 AM
To:  Tesla List
Subject:  Re: FW: Which DC Drive?

At 01:05 10/06/98 -0500, you wrote:
>(The DC supply itself uses two MOTs tied together and grounded at their
>cores, acting the same as a NST.  Each MOT "side" has its own 2-diode
>voltage doubler.  So MOT voltage breakdown is not a problem.  See below.)  
>
>             MOT     C        D1                               C pri
>             |||0---||----|--|>|--|--- + about 5 KV ------|---||-----|
>     -------0|||0         |       |                       |          |  
>            0|||0    |-|>|-      --- C1 (don't need?)      |          |  
>     -------0|||0    |  D        ---                      |        L 0
>             |||0----|------------|---- Gnd               o      pri 0
>                     |                                    o gap      0
>             |||0----|------------|                       o          0 
>     -------0|||0    |           ---                      |          | 
>            0|||0    -|<|-       --- C2 (don't need?)      |          |
>     -------0|||0      D |        |                       |          |
>             |||0---||----|--|<|--|--- - about 5 KV ------|----------|
>             MOT     C        D2
>

Steve, I am too using two MOT (Microwave Oven Transformers?). If you check
my old mails to
Tesla List you'll find my schematics and an analysis of the output voltage
waveforms. Two
points:

1. If you use my scheme you save 2 diodes and 2 capacitors: in your scheme,
when the gap
fires it is possible that D1 and D2 will experience high currents that will
blow them.
Those from microwave ovens usually stand about 400 mA.

2. What I have been able to test until now with my supply is that, when the
gap fires, the
MOTs pump up to 0.5A (not 30 mA as from a NST!) through the gap. This makes
a nice 10A on the
110 VAC side, multiply by two (two MOTs) and you get 20A ---> mains fuse blows.

Thinking to a resistive shunt I made a 20 KOhm water resistor (10 cm lenght
X 16 mm diameter
water hose) and put it in series with the spark gap: 5 seconds (five) of
sparking through the gap
was enough to expand and nearly melt the resistor hose :) Not good...

My explanation is that, when the spark gap fires, the MOTs pump in it each 1
KW (total 2 KW)
and they can do it until your fuse blows or the gap quenches. Now imagine to
tune your TC
keeping initially the gap close: that means the gap will fire for a
considerably LONG part
of the 60 Hz cycle (and during that time you'll have to "handle" those 2 KW
somewhere...).


I am thinking about all this and trying to simulate to whole circuit with
MicroCap.

Help from everybody is really needed, but please don't just tell me "Use a
NST, idiot!" :)



________________________________________________________________________

 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...
________________________________________________________________________