Control circuit for starting a motor

Claim 1

In a power supply circuit having a motor arranged in series with an SCR starter and a power source, and having a bypass circuit arranged in parallel with said SCR starter, said power supply circuit further including a main contactor operatively arranged between said SCR starter and said power source, and a bypass contactor arranged in said bypass circuit, the improvement which comprises: a control circuit operatively associated with said power supply circuit for limiting the in-rush current supplied to said motor when said motor is initially started, and for supplying current to said motor through said bypass circuit after said motor has reached its operating speed, said control circuit including first branch circuit means arranged to be supplied with a control voltage and having a selectively operable control switch, having a main operator operatively arranged to close said main contactor when said control switch is closed, and having a first timer for measuring a first time interval after said main operator has been operated; second branch circuit means arranged in parallel with said first branch circuit means and having a trigger circuit operatively arranged to fire said SCR starter after said first time interval, and having a second timer for measuring a second time interval after said trigger circuit has been operated; and third branch circuit means arranged in parallel with said first branch circuit means and having a bypass operator operatively arranged to close said bypass contactor after said second time interval, having a third timer for measuring a third time interval after said bypass operator has been operated, and having means for opening said second branch circuit after said third time interval; whereby said SCR starter may be removed from said power supply circuit after said third time interval.