RE: Ballast question (fwd)

[<sroys@xxxxxxxxxxxxxxxxx>]

---------- Forwarded message ----------
Date: Thu, 18 Nov 2004 09:27:46 -0600
From: Carl Litton <Carl_Litton@xxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: RE: Ballast question (fwd)

Hello Godfrey,

What an incredible resource this list is!  Thank you for the clear and
helpful explanation.

Carl Litton


-----Original Message-----
From: High Voltage list [mailto:hvlist@xxxxxxxxxx] 
Sent: Wednesday, November 17, 2004 9:58 PM
To: hvlist
Subject: RE: Ballast question (fwd)

Original poster: <sroys@xxxxxxxxxxxxxxxxx>



---------- Forwarded message ----------
Date: Wed, 17 Nov 2004 17:44:06 -0600
From: Godfrey Loudner <ggreen@xxxxxxxx>
To: 'High Voltage list' <hvlist@xxxxxxxxxx>
Subject: RE: Ballast question (fwd)

Hello Carl

You already discovered the answer in your experiments. Take two coils A
and B on a core. If coil B is not shorted, then the inductance of coil A
is determined only by the shapes of coil A and the core. In Mot's and
power transformers, the inductance of coil A is too high and will allow
too little current to flow through coil A for our purposes. But if coil
B is shorted, the current flowing in coil B will add a magnetic field to
the core that will lower the inductance seen by coil A. Now more current
can flow through coil A. If one is lucky, the amount of current might be
just the current limiting desired.   

Godfrey Loudner      

-----Original Message-----
From: High Voltage list [mailto:hvlist@xxxxxxxxxx] 
Sent: Wednesday, November 17, 2004 9:26 AM
To: hvlist
Subject: Ballast question (fwd)


Original poster: <sroys@xxxxxxxxxxxxxxxxx>



---------- Forwarded message ----------
Date: Tue, 16 Nov 2004 16:48:37 -0600
From: Carl Litton <Carl_Litton@xxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Ballast question



Carl Litton

Hello

Thanks to everyone who responded on the transformer stack question.
Tremendous amount of useful knowledge gained that is much appreciated.

We have now gotten the use of a very nice inductance meter, measuring up
to 500 Henries.  Of course, we immediately set about measuring every
possible combination of ballasting devices with a wide variation in the
results from a few microhenries to one that was 300 Henries.  One of the
things we did with large frame transformers was to measure the primary
winding with secondary short and open and the secondary winding with
primary short and open.  

Without exception, the inductance of a transformer winding is several
orders of magnitude higher when the other winding is open.  Shorting the
other side drops inductance usually into the microhenries.

The question is:

Why is it that it is almost uniformly recommended that transformers used
for ballasting (MOT's mostly) have the magnetically coupled winding
shorted?  Is this related to changing the inductance or simply to
prevent arcing?


All comments appreciated,

Carl Litton