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 20:36:53 -0500
Approved: tesla-at-stic-dot-net

----------
From:  Malcolm Watts [SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent:  Wednesday, June 10, 1998 3:36 PM
To:  Tesla List
Subject:  Re: FW: Which DC Drive?

Hi Steve,

> From:  Steve Young [SMTP:youngs-at-konnections-dot-com]
> Sent:  Monday, June 08, 1998 11:34 PM
> To:  Tesla List
> Subject:  Re: Which DC Drive?
> 
<snip>

> Greg,
> 
> Thanks for the reply.  Yes, my DC supply will be self-current limiting,
> thanks to MOT mag shunts.  My idea for also using a charging reactor (e.g.
> made with secondary of one or two additional MOTs) was to prevent the spark
> gap from completely discharging the supply output filter cap on every bang,
> requiring the supply to completely recharge it.  I thought with a reactor,
> the supply output cap would supply roughly only enough energy to charge up
> the TC primary cap.  This assumes use of a RSG and a long enough time
> constant (reactor & supply cap) that the RSG would stop conducting before
> all the supply cap energy was dissapated across the gap.  The idea was to
> improve efficiency and reduce spark gap electrode erosion. 
> 
> But on further thought (inspired by your post), voltage doublers don't
> really need an output cap as long as they are supplying a capacitive load,
> such as the TC primary cap.  Eliminating the supply output cap would also
> eliminate any need for a charging reactor.  I will give this a try, but all
> comments on this approach are welcomed!      
> 
> (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        D                               C pri
>              |||0---||----|--|>|--|--- + about 5 KV ------|---||-----|
>      -------0|||0         |       |                       |          |  
>             0|||0    |-|>|-      --- C (don't need?)      |          |  
>      -------0|||0    |  D        ---                      |        L 0
>              |||0----|------------|---- Gnd               o      pri 0
>                      |                                    o gap      0
>              |||0----|------------|                       o          0 
>      -------0|||0    |           ---                      |          | 
>             0|||0    -|<|-       --- C (don't need?)      |          |
>      -------0|||0      D |        |                       |          |
>              |||0---||----|--|<|--|--- - about 5 KV ------|----------|
>              MOT     C        D

Take a careful look at the equivalent circuit when the gap fires - 
your filter caps will directly discharge themselves through the gap
without doing any useful work.
 
Malcolm

> Suppose I knocked out the MOT magnetic shunts, or had some other "hard" DC
> supply.  Again, what are guidelines for sizing a current-limiting charging
> reactor?
> 
> Thanks in advance for comments,
> 
> Steve