Re: Welders

Quoting Justin Hennigan <JustinH-at-Interlaced-dot-net>:

> How do you use a welder in Tesla coil applications.
> Do you use it for a ballast?  Or as a power supply?

A welder is placed in series somewhere in the control 
circuit to current limit (ballast) the step-up transformer.


On Fri, 8 Sep 1995, Mark Barton wrote:

 > A large series variable inductor is a must when using          
 > non-limited transformers.  It is usually made by connecting up 
 > to 2 leads of a Variac (one end and the wiper).

I have never been happy with a variac as a variable inductor for
ballasting (external current limiter). Variacs are designed not
to saturate in order to efficiently transform current. While I
have seen people use them, they really only have two settings, on
and off. The actual variable current limiting on a variac occurs
on just a couple of turns on the winding. There is simply not
enough smoothly variable inductance available to give good
control over a wide range of transformer input currents.

Quoting Harri S.

> The inductor would need to be huge. Or are you talking about  
> variac limiting on the primary side?

Yeah, the current limiting is placed in series with the primary
winding of the step up xfmr.

On Sat, 9 Sep 1995, Richard Quick wrote:

 > I have never been happy with a variac as a variable inductor  

Quoting Harri S.

 > What is a better choise? Air coils are certainly out becouse of
 > the huge size. Making other huge inductor is probably out too.
 > (Well, actually a big enough core would do the job w/o saturation).
 > Resistive methods work but are not too appealing. Still some
 > methods available I haven't figured out yet?

Here in the states most of us use a commercial electric arc welder
at some point or another. Commercial electric arc welders are not 
too expensive, easily obtained, fully rated for the primary current
typical of medium and high powered coiling, and provide a wide var-
iety of different tap or shunt positions that gives a wide range of
fully controlled current settings.

Wiring one in the circuit is easy. Simply place the primary winding
on the arc welder in series with the variacs. Short the secondary
on the arc welder. By adjusting the arc power level on the welder
the current through the variacs is varied. Arc welders do have one
problem though; inductive delay. Given the large mass of core and
copper in a Tesla coil system where a heavy step-up xfmr is used
with external current limiting, the inductive delays can exceed one
full second! You have the inductance of the current limiter, the
variac core(s), the step-up transformer core itself; it is not at
all unusual for the mass of copper and core to exceed several 
hundred pounds.