[Prev][Next][Index][Thread]

Re: Inductive Ballasting

> 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
> transformer.
> 
> 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.
> 
> Richard Quick
> 

Excellent explanation. Thank you. I just want to make sure if I am clear on
a few points.

Tesla coil is essentially a transformer (with a distributed and lumped tuned 
circuit) in the secondary and intermittent make and break circuit in the 
primary. The output voltage of this can be varied by changing the input 
voltage using variacs. The output current can be limited by varying the
input current. This is accomplished without losses using a large inductor,
also called ballast or choke by the lighting and other industries. One place
this inductor is found is the arc welding power supply.

The arc welding power supply is essentially a stepdown transformer with a
current limit in series with the primary. The transformer which is an infinite
inductance is shorted out by shorting the secondaries (convenient trick) and
then this is used as the inductor.

Is this a correct understanding of the setup?

My question is if the welding supply has any other circuitry such as
SCR/Triacs for conduction angle modulation in series with the primary?

lbliao