Method and apparatus for preventing overheating in an electronically commutated motor assembly

A control circuit for operating a motor having a rotor and a stator, the stator having a stator winding, the control circuit comprising:

• a switching device controlling power supply to the stator winding;
• a switching device driver controlling the operation of the switching device;
• a voltage regulator circuit connected to the switching device driver;
• a temperature sensing device adapted to sense the temperature of the voltage regulator circuit;
• and
• a thermal shutdown device adapted to shutdown the voltage regulator circuit in response to the temperature of the voltage regulator being above a threshold level;
• a micro-controller further adapted to detect an unexpected drop in the speed of the rotor and to generate an error code in response to detection of the drop in the speed of the rotor.

A vacuum cleaner having a motor and a load attached to the motor, the motor having a rotor, and a stator having a stator winding, the motor being operated by a control circuit, the control circuit comprising:

• a switching device controlling power supply to the stator winding;
• a switching device driver controlling the operation of the switching device;
• a voltage regulator circuit connected to the switching device driver;
• a temperature sensing device adapted to sense the temperature of the voltage regulator circuit;
• and
• a thermal shutdown device adapted to shutdown the voltage regulator circuit in response to the temperature of the voltage regulator being higher than a threshold level;
• a controller coupled to the switching device driver,
• wherein the controller detects the slow down of rotor speed below a set value and prevents a restart of the motor absent cycling off and on of the motor starter switch.

A method of operating a motor to prevent unintended restarting of the motor following an over-temperature condition absent subsequent cycling off and on of a motor starter switch, the motor having a control circuit, a rotor, and a stator having a stator winding, the control circuit having a controller and a voltage regulator having an thermal shutdown device for shutting down the voltage regulator when the temperature of the voltage regulator exceeds a threshold temperature, the voltage regulator for supplying power to the stator winding via a switching device and switching device driver in response to switching device control signals from the controller to the switching device driver, the method comprising:

• measuring a temperature of the motor with the thermal shutdown device;
• monitoring the rotational speed of the motor;
• turning off the voltage regulator if the measured temperature indicates an over temperature condition, thereby shutting down power to the stator winding, while maintaining power to the controller;
• and
• preventing a restart of the motor upon cooling of the thermal shutdown device absent a cycling off and on of the motor starter switch if the rotational speed of the motor drops below a threshold value.

A control circuit for preventing an unintended restarting of a motor following an over-temperature condition of the control circuit, absent cycling off and on of a motor starter switch, the motor having a rotor and a stator, the stator having a stator winding, the control circuit comprising:

• a switching device controlling power supplied to the stator winding;
• a switching device driver controlling the switching device;
• a voltage regulator circuit providing power to the switching device driver, the voltage regulator including a thermal protection device to shut down the voltage regulator in response to the over-temperature condition;
• circuitry for detecting the rotational speed of the rotor;
• and
• a controller coupled to the speed sensing circuitry and the switching device driver,
• wherein shutting down of the voltage regulator shuts down power to the stator winding, causing the rotor to drop in speed;
• and
• wherein the controller detects the slow down of rotor speed below a set value and prevents a restart of the motor absent cycling off and on of the motor starter switch.