Re: Arc welders as curent limiters

I'll give this one a shot...

You short the output terminals of the welder and place the primary of the
welder in series with your application.
You move the crank on the welder to adjust the inductance of the core and
hence the current flow through the device.

I'll try to explain using an inductor to limit current:

In DC circuits, we know that Ohms law governs current flow by I = V/R.
In AC circuits, we have to get a bit more complicated and consider the effects
of inductance and capacitance.
For AC, we can say that I = V/Z, where Z is known as impedance.
Impedance = Reactance + Resistance
Reactance is created by inductance (L) or capacitance (C)
The formula for inductive reactance (in Ohms) is
Z(L) = 2*pi*F*L,   where F is frequency in Hz

It makes some of out EE friends cringe, but it has been said that an inductor
acts like a "frequency variable resistor".
At low freqs the DC resistance dominates and at high freqs the inductive
reactance dominates.
People have successfully used welder cores, homemade wound inductors, NST
primaries, MOTS, variacs, etc.

The interesting part happens when enough current flows through your inductor
to saturate the core.  When
the core begins to saturate, the inductance decreases.  A decrease in
inductance leads to a decrease in impedance which leads to more current.  The
cycle continues until the DC resistance determines the max current flow.
Oftentimes, this current is much more than the wire in the inductor can handle
and things burn up.

BTW, the ARRL Handbook has some very well written chapters on basic
electronics.  The technical data is there for those who want to dig deeper,
but the text is written with the novice in mind.  Although it's written by and
for the HAM crowd, it has tons of great info that is applicable to Coilers.
It's about 1200 pages, cost about $35, and can be ordered from
http://www.arrl-dot-org or found at most large bookstores.

Hope this helped,
Making Arcs in Huntington Beach,
Ross Overstreet

Tesla List wrote:

> Original Poster: "Norman F. Stanley" <nfs-at-midcoast-dot-com>
> I've seen references on this list to the use of arc welders as current
> limiting devices in the primary circuits of large transformers for Tesla
> coil operation.  Although my application is non-TC, I do need to limit the
> current drawn by a 12 KVA 206 ro 30V transformer under short circuit
> conditions.  Could some kind soul explain how the welder is hooked up to
> perform this function?  Reply off-list if the subject is too off-topic.
> Thanks.
> Norm