Re: Microwave Oven Transformers (MOTs)

To: tesla-at-pupman-dot-com
Subject: Re: Microwave Oven Transformers (MOTs)
From: "J. B. Weazle McCreath" <weazle-at-hurontel.on.ca> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Wed, 26 Apr 2000 10:35:27 -0600
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

At 08:53 PM 25/04/00 -0600, you wrote:
>Original Poster: "Gavin Dingley" <gavin.dingley-at-astra.ukf-dot-net> 
>
>Hi all,
>
>You can connect the 240V primary windings of two MOTs in anti-phase
>parallel, while connecting the ~2.5kV secondary windings in series. This
>results in a supply that can deliver ~5kV -at- 250mA upto 1A?
>
>As one of the secondary leads are connected to the core, electrically
>you connect the HV lead from one transformer to the core of the next
>transformer secondary?
>
>Well, I'll leave it at that to get the ball rolling.
>
>Regards, Gavin, U.K.
>
>
Hello Gavin:

For the sake of the explanation I'm assuming that your two MOT's are
of the same make and model.  That being the case, connect the two
cores together solidly, both electrically and mechanically.  This is
the point that will be solidly grounded to your TC ground when you
connect things up for use.

With the primary terminals are facing you, label the terminals one and
two on both transformers, making sure they are the same on each.  Then
connect terminal 1 of left transformer to terminal 2 of the right, and
terminal 2 of the left transformer to terminal 1 of the right. This is
done so that the two primaries are in parallel but 180 degrees out of
phase, which is what you want.

With the above hookup complete, apply power to the transformers with
either a variac or a 100 watt light bulb connected in the hot power
lead to limit the current.  Using EXTREME CAUTION and well insulated
leads, you should be able to draw a pretty good arc between the two
H.V. leads, one from each transformer, if all is working as it should.
If you have a meter with a high enough range you should measure about
5000 volts between the two secondary leads, or twice the voltage of
one transformer by itself.  

As far as current limiting is concerned, you can use either a resistor
or an inductor, or even a combination of both, to keep the primary
current under control.  Some of the fellows use a third MOT with the
secondary leads shorted together as an inductor.  Just connect its
primary in series with the hot lead of your power cord.

73, Weazle, VE3EAR/VE3WZL

Listening: 147.030+ and 442.075+
E-mail:    weazle-at-hurontel.on.ca
           or ve3ear-at-rac.ca
Web site:  www.hurontel.on.ca/~weazle