Power efficient motor starter and circuit breaker for an induction motor

Claim 1

A starting and thermal overload protection circuit for a motor having at least one main coil and a starter coil arranged in parallel comprising: a power source having at least first and second power supply terminals, said first power supply terminal serially connected to said motor coils; overcurrent protection means for protecting said motor from an overcurrent, said overcurrent protection means including, a conductive bimetallic contact support, and at least one moveable contact mounted thereon interacting with a stationary contact, said stationary and moveable contacts and said bimetallic support being serially connected between said second power supply terminal and said main coil to provide power from said power source to said motor, said moveable contacts being normally in contact with said stationary contacts, said bimetallic contact support moving said moveable contact away from said stationary contact when an overcurrent heats said bimetallic contact support; and means for supplying a starting current to said motor coil, said means for supplying including, a positive thermal coefficient resistance mounted in juxtaposition to said bimetallic contact support and electrically connected thereto, a triac serially connected between said positive thermal coefficient resistance and said starter coil for controllably supplying current thereto for motor starting, current sensing means for detecting current supplied said main coil by said power source, means, operatively interconnected between said triac and current sensing means, for gating said triac ON only in response to a detected current substantially greater than the normal current supplied to said main coil during normal operating conditions, and a phase control capacitance interposed between said triac and said means for gating and ensuring substantially complete conduction of said triac when gated ON by said means for gating.