Motor heating unit with power failure control responsive to an unheated condition of the motor

Claim 2

A motor heating unit with power failure control for maintaining an electric motor in a warm condition after the motor has been turned off and preventing reapplication of power after a power failure until the motor is heated, comprising, in combination: a main power source connected to said motor; power switch means between said power source and motor for turning on and turning off said motor; an auxiliary source of electrical energy derived from said main power source; means for connecting said auxiliary source of electrical energy to the windings of said motor in response to opening of said power switch means and disconnecting said auxiliary source of electrical energy from said windings in response to closing of said power switch means; and sensor means connected to said power switch means and responsive to an unheated condition of said motor to open said power switch means and prevent reapplication of power to said motor in the event of a power failure and subsequent reapplication of power, until said motor is heated.

Claim 3

A motor unit with power failure control for maintaining an electric motor in a warm condition after the motor has been turned off and preventing reapplication of power after a power failure until the motor is heated, comprising, in combination: terminal means connected to the windings of said motor; a main power source connected to said terminal means; power switch means between said power source and terminal means for turning on and turning off said motor; an auxiliary source of electrical energy; heating switch means for connecting said auxiliary source of electrical energy to said terminal means when closed; time delay means responsive to turning off of said motor for closing said heating switch means after a given length of time at least as long as the time for said motor to come to rest after being turned off; and sensor means connected to said terminal means and said power switch means responsive to a decrease in the resistance of said windings in said motor below a given value to open said power switch means and prevent reapplication of power to said motor in the event oF a power failure and subsequent reapplication of power, until said motor is heated sufficiently by said auxiliary source of electrical energy to raise said resistance above said given value.

Claim 4

A motor unit with power failure control for maintaining an electric motor in a warm condition after the motor has been turned off and preventing reapplication of power after a power failure until the motor is heated, comprising, in combination: terminal means connected to the windings of said motor; a main power source connected to said terminal means; power switch means between said power source and terminal means for turning on and turning off said motor; an auxiliary source of electrical energy; heating switch means for connecting said auxiliary source of electrical energy to said terminal means when closed; time delay means responsive to turning off of said motor for closing said heating switch means after a given length of time at least as long as the time for said motor to come to rest after being turned off; and sensor means connected to said terminal means and said power switch means responsive to a decrease in the resistance of said windings in said motor below a given value to open said power switch means and prevent reapplication of power to said motor in the event oF a power failure and subsequent reapplication of power, until said motor is heated sufficiently by said auxiliary source of electrical energy to raise said resistance above said given value.

Claim 5

A unit according to claim 2, in which said auxiliary source of electrical energy includes a transformer having its primary connected to said main power source and its secondary connected to said heating switch means.

Claim 6

A unit according to claim 3, in which said secondary of said transformer includes a plurality of tap points so that different voltages to be applied to said terminals through said heating switch means may be selected.

Claim 7

A unit according to claim 3, in which said transformer is a step down transformer such that current supplied to said motor falls within a range of from one-half to one-sixth the current rating of said motor.