Arc welder

In an arc welder:

• input terminals for receiving an a.c. power,
• an input rectifier for rectifying said a.c. power,
• a pair of capacitors connected in series between output terminals of said input rectifier for smoothing an output thereof,
• a pair of invertors respectively driven by outputs of said capacitors for generating high frequency outputs,
• an output transformer for transforming outputs of said invertors,
• an output rectifier for rectifying an output of said output transformer,
• a control transformer having a pair of primary windings connected in series between said input terminals,
• a d.c. convertor for rectifying and smoothing an output of said control transformer to produce a d.c. control voltage,
• means for changing connections of said capacitors and said primary windings of said control transformer from series to parallel when said control voltage is lower than a first predetermined value, and
• means for holding said connections in parallel regardless of increase in said control voltage due to said change of the connections;
• the improvement comprising:
• initializing means for temporarily shutting off said a.c. power to release operation of said holding means when said control voltage is higher than a second predetermined value.