Re: MOT to NST "extra transformer"

To: tesla-at-pupman-dot-com
Subject: Re: MOT to NST "extra transformer"
From: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz> (by way of Terry Fritz <terryf-at-verinet-dot-com>)
Date: Thu, 24 Sep 1998 04:13:46 -0600
Approved: terryf-at-verinet-dot-com

Hi Terry,
          Running with 2kV on the primary will necessitate a lot of 
primary inductance:

> Original Poster: Terry Fritz <terryf-at-verinet-dot-com>
> 
> Hi All,
>     I am going to get a MOT to play with and a thought occurred to me
today. 
> 
> Most MOTs (microwave oven transformers) put out about 2000 volts at 300 mA.
>  The voltage is too low and current too high for most TC applications.
> However, how hard would it be to make a transformer to bring it to a nice
> level?  Perhaps a 2000V/300mA primary and a 12000V/50mA secondary.  Since
> the turns ratio would only be six to one, there should be room to use
> insulated 24 gauge wire on the secondary which would make it almost burnout
> proof (in oil).  In fact, two or more MOTs could be used to drive this
> "extra transformer".  The current protection in the original MOT should
> function normally (I think).
>     Since the number of secondary turns is much less than say a 120v to
15000v
> transformer, such an extra transformer would be much easier for the average
> person to wind.  With 24 gauge insulated wire in oil with poly between
> layers, It would be burnout proof no matter how hard it was hit.  It would
> still need to be rated for 900VA and one would have to do a little design
> work but this may solve the problem of not being able to get HV
> transformers in certain countries and all that.
> 
> Comments?
> 
>     Terry Fritz

and as the core gets smaller, the inductance must rise to keep Imag 
from saturating the core. I don't think you'll be much better off
sizewise. Equations worth noting:

Magnetizing force = Np*Imag
Imag = Vp/2*PI*Fmains*Lp
Lp = k*Np^2                where k is a core induction constant

If Np halves, Lp quarters and Imag doubles.  Nub of the problem is 
that the core can only support so many Ampere-turns before it 
saturates. For good transformer operation the core must be ungapped
so core area becomes a critical factor (flux density or flux/area^2)
Effective core length does not greatly influence maximum core flux in 
an ungapped design and really only exists to allow a winding window
which in turn allows copper mass for a power rating.

Malcolm