Re: Inductive Ballasting
Subject: Re: Inductive Ballasting
From: richard.quick-at-slug-dot-org (Richard Quick)
Date: Tue, 12 Sep 1995 18:33:00 GMT
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Quoting gcerny-at-ix-dot-netcom-dot-com (Glenn Cerny ):
GC> I guess I still don't get it. Sorry, I am a little slow at
GC> times. Does a coiler connect to the secondary of the welder
GC> or the primary with his feeder leads? I assume that the
GC> welder winding that is not used is simply "stored".
Current limiting (ballast) is usually placed in series with the
240 volt 50/60 cycle mains somewhere between the breaker box and
the primary winding on the step up transformer (xfmr). Current
limiting can be resistive, inductive, or a combination of both.
When using an arc welder as a current limiter, the primary
winding on the welder is placed in series with one leg of the 240
volt 50/60 cycle feed to the step up xfmr. Now we want current to
flow through this circuit, we simply want to be able to control
the amount of current. In order for current to flow at all, the
secondary winding on the arc welder, that is the welder cables
themselves, must be shorted out. The welding cables are equipped
with clamps, so I just clamp the ends of the cable together.
Now current will flow through both windings on the welder. The
low voltage secondary winding is shorted, the 240 volt primary
winding is in series with the step up xfmr.
The welder will be equipped with some means of increasing and
decreasing the power that is supplied to the welding arc. By
power what we really mean is current. A dial, slide bar, tap
holes, or the like is used vary the current that is supplied to
the welding arc. With the secondary winding directly shorted
there is virually no resistance or impedance to current flow
here. If it were not for the inductive current limiting designed
into the welder core, every you struck a welding arc the breakers
would trip and/or things would get pretty dark. The welder is
designed to operate with a low impedance (even a dead short)
across the secondary winding for limited periods of time,
described as the "duty cycle" which will be noted somewhere in
the manual or on the welder case.
With the 240 volt primary winding of the welder wired into the
coil control circuitry as outlined above, the current settings on
the welder are in effect limiting the number of amps at ~240
volts (there is some voltage drop) that are allowed to pass
through the primary winding on the step up xfmr. When you
increase or decrease the power setting on the welder cabinet, you
are increasing or decreasing the current available to the step up
This is the simple way to wire things. When operating Tesla coils
I like to have control over the voltage as well as the current.
Variacs are available off the shelf that can be ganged together
to handle all of the current that can be passed through the arc
welder primary. In actuality I run the arc welder primary in
series with the variacs in my control cabinet. The outputs from
the variacs are sent to the step up xfmr, and it is this output,
or "conditioned power", that I monitor with the meters in the
control cabinet face.
... If all else fails... Throw another megavolt across it!
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