winding your own transformer

From:  D.C. Cox [SMTP:DR.RESONANCE-at-next-wave-dot-net]
Sent:  Tuesday, January 27, 1998 12:31 AM
To:  Tesla List
Subject:  Re: winding your own transformer

to: Travis

The reason for center-tapping a transformer is simple:  Let's assume you
have an X-ray tube (or neon sign) that requires 20 kiloVolts to operate
effectively.  You could build a xmfr and insulate the secondary winding for
the full 20 kV, but it is a lot easier to wind two separate windings each
rated for 10 kV -- one winding is reversed so that while it is hitting 10
kV positive on the 60 Hz sine wave the other winding is hitting 10 kV
negative on the sine wave.  The effective potential between the two
windings is 20 kV to run the tube, however, the insulation and spacing from
the metal case only has to withstand 10 kV --- it's almost like cheating. 
This principle was using for many X-ray xmfrs running up to 200 kV output
with insulation for only 100 kV necessary internally.  The Boston Museum of
Science Van de Graaff was once actually two units -- one running 5 million
volts plus while the other was 5 million volts minus -- the accelerator
tube used between the units was "seeing" 10 million volts between them.

Hope this helps clear up the mystery.


> From: Tesla List <tesla-at-pupman-dot-com>
> To: 'Tesla List' <tesla-at-pupman-dot-com>
> Subject: winding your own transformer
> Date: Monday, January 26, 1998 8:14 PM
> ----------
> From:  Tabbal [SMTP:bigboss-at-inquo-dot-net]
> Sent:  Monday, January 26, 1998 4:00 AM
> To:  Tesla List
> Subject:  Re: winding your own transformer
> > I've had quite a bit of experience with transformers.  I've worked with
> > tesla coils for about 18 yrs. now and have been a High Voltage, High
> A question for the Transformer experts out there... Why do we center-tap
> them? I just haven't been able to figgure out what this does. 
> Also, I have a project I'm looking at that calls for the following custom
> transformer..
> 4 turns, center-tapper primary, 16 turns, center-tapped secondary; 5-mil
> copper foil wound on a Ferroxcube ETD-34 core.
> So, the center-tap question applies here, but do they want the actual
> windings to be copper foil? Seems like an odd matterial to use for a
> Transformer. I assume it must be insulated by me with paper or something.
> Would Polyethelene work? It's for lower voltages, should peak at about
> 60v. 
> If it is to be wound with foil, the tap could just be a wire soldered on
> at the middle of the winding, right?
> Travis