Welding transformers obviously must be designed to withstand a very low
impedance short circuit across its secondary output winding (within a
reasonable duty cycle) when the welder strikes an arc with it. Therefore,
shorting the secondary (work) winding while the primary input is in series
with the primary of the step up transformer is actually staying pretty much
within the design parameters of the welding transformer - especially when
you consider that most coiling is also done on a very limited duty cycle.
David
----- Original Message -----
From: "Ronald Reeland" <ronreeland@xxxxxxx>
To: "TESLA COIL MAILING LIST PUPMAN" <tesla@xxxxxxxxxx>; "Ronald Reeland"
<ronreeland@xxxxxxx>
Sent: Monday, June 04, 2018 3:58 PM
Subject: [TCML] Welding Transformer As Ballast or Choke
Hi:
I am trying to understand how a welding transformer functions as a ballast
choke to limit surge current thus preventing circuit beakers tripping. I
get the fact that the welder has a heavy gage winding and can handle high
currents. And it has a certain inductance figure that presents inductive
reactance at or impedance at 60 Hertz to changes or surges in current. But
I am baffled as to why the welder has its secondary side shorted out when
used as a ballast choke.
A basic transformer has its highest impedance or inductive reactance on
its primary when there is no load on the secondary. As the secondary load
increases, primary reactance decreases and primary current increases. So
if you short the secondary, that is maximum load causing the primary
reactance to greatly decrease thus raising the primary current to a
maximum. ( And burning up the transformer as a result.)
So it seems to me that an unloaded secondary is the best situation while
using a primary as a choke coil.
And yet, Tesla coilers seem to get best results with a shorted secondary
on the welding transformer. Please explain.
Thanks,
Ron Reeland
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