Re: Microwave Transformers / Capacitors

To: tesla-at-pupman-dot-com
Subject: Re: Microwave Transformers / Capacitors
From: Thomas McGahee <tom_mcgahee-at-sigmais-dot-com>
Date: Wed, 22 Jan 1997 03:39:59 -0500
Subscriber: tom_mcgahee-at-sigmais-dot-com Wed Jan 22 21:32:59 1997
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> From: Tesla List <tesla-at-poodle.pupman-dot-com>
> To: Tesla-list-subscribers-at-poodle.pupman-dot-com
> Subject: Re: Microwave Transformers / Capacitors
> Date: Friday, January 17, 1997 12:58 AM
> 
> Subscriber: 100624.504-at-CompuServe.COM Thu Jan 16 22:53:22 1997
> Date: 16 Jan 97 11:15:37 EST
> From: Alan Sharp <100624.504-at-CompuServe.COM>
> To: Tesla List <tesla-at-poodle.pupman-dot-com>
> Subject: Re: Microwave Transformers / Capacitors
> 
> Greetings all,
> 
> >Bottom line is that two microwave oven transformers CAN be used to
produce
> >a quite powerful Tesla coil if you pay close attention to the spark gap,
> >capacitor, primary, secondary, and use a toroid on the secondary.
> 
> Great I have two microwave transformers and they seem to be easier to
> come by over here (UK). And while I'm busy with FET's at the moment
> I do want to build a traditional coil sometime.
> 
> >To use two transformers you first connect the frames together. This will
act
> >as a frame-connected center tap. Note that all this means that this
> >arrangement is subject to all safety precautions pertinent to high
voltage
> >transformers with a center tap attached to their case or frame.
> 
> I do have one question is it possible to arrange things so that the frame
> connected centre taps are both connected to ground, (primaries
> connected in anti //.
> 
> +/- 2500V
> 0
> 0
> 0
> ---- GND
> 0
> 0
> 0
> -/+ 2500V
> 
> The capacitor would be two caps in series centre tapped to ground, the
gap and
> the primary connected across the capacitors, plus chokes on both sides
and
> safety gaps to ground on both sides.
> 
> This arrangement would avoid raising the frame to 5KV relative to the
mains
> voltage
> primary. But it needs two (lower voltage) capacitors.
> 
> >Fr. Thomas McGahee
> >(Yep, I am a 50 year old priest that has taught electronics for 30
years. 
> 
> Yes, but shouldn't we clergy leave the lightning bolts to our Boss!
> 
> Have fun!
> 
> Alan Sharp (minister, Church of Scotland)

Ah, it is always Good to meet another Follower and Minister of Jesus
Christ! THAT is my absolute Greatest Joy... To be HIS!

To answer your question: Yes, you can wire things up the way you described,
but you need to understand what the Problem is with this arrangement.
(EVERY posible arrangement that you can think of using a frame grounded
center tap circuit has one Problem or another, so don't worry too much)  

If you draw out the circuit on paper you can see the Problem fairly
clearly.  Now there are TWO ways you MIGHT ATTEMPT to connect the Bottom of
the Tesla Secondary. The REALLY BAD Way is to connect it to the Primary.
This will not work, because when the Tesla Coil TOP strats to shoot out
sparks it is electrically PUSHING against the bottom of the coil. But since
the NEAREST GROUND CONNECTION is the Frame Center Tap, it gets there
THROUGH the Lower transformer HV winding which has a Realtively High
Inductance. So it BLOWS through the insulation and Kills the bottom
transformer. Not too Good!

The only VIABLE way of connecting is to NOT connect the Tesla Secondary to
the Primary circuit AT ALL. Connect the Tesla Secondary to a really Good
Earth Ground. There is still a Problem, but one we have more control over!
The potential between the Tesla Primary and Tesla Secondary Bottom Windings
is now 1/2 of the Power Supply HV value due to the Center Tap Connection.
This is OK so long as you absolutely ensure that there is no chance of
ARCING between the Tesla Primary and the Tesla Secondary (Which have 1/2
the HV between them). Any ARCing HERE will effectively be a DEAD SHORT
between the Tesla Primary and GROUND. So the Lower half of the transformer
would be at Risk. But ONLY IF AN ARC OCCURS. Just make sure the Tesla
Primary and secondary are extremely well separated along their entire
length. 

Hope this answers your question.

If all else fails, try something else.
Fr. Tom McGahee