Constant current arc welder

Claim 1

In a direct current arc welder having an arc-gap supplied with power through SCR devices and saturating reactor means, a controller for said SCR device including voltage feedback control means operative to establish a predetermined constant voltage between said arc-gap and current feedback control means operating with a predetermined gain and under a predetermined reference signal to establish a predetermined constant current through said arc-gap; the combination of: timer means initiated at start-up by a predetermined buildup of arc current under said constant voltage for establishing a time interval; with said current feedback control means having a first operative mode under a reference signal substantially reduced from said predetermined reference signal and a gain reduced from said predetermined gain; a second operative mode under said predetermined reference signal and with said predetermined gain; means responsive to initiation of said time interval for disabling said voltage feedback control means and for enabling said current feedback control means in the first mode, whereby arc-gap current is limited, by said current feedback control means and by said saturable reactor means concurrently, at the end of said time interval to a current level higher than said constant current level; means responsive to expiration of said time interval for transferring said current feedback control means into the second mode; and feedback loop means associated with said current feedback control means and operative at the end of said time interval for smoothly lowering the arc-current from said higher level to said predetermined constant current level as a function of time.