Control for intermittently loaded electric appliance

An electric appliance comprising:

• an electric motor:
• an electrically controlled switch connected in series with a conductor arranged to deliver operating power to the motor, and openable in response to a control signal to interrupt the delivery of operating power to the motor;
• a current sensor arranged to sample the current drawn by the motor, and providing a signal representative of the load on the motor;
• and
• a microcontroller responsive to said signal and programmed to:
• (a) determine when the current drawn by the motor has fallen below a threshold current level greater than the level of an idling current drawn by the motor after the motor is turned on but before the motor is under an operating load but less than the level of the current drawn by the motor when under said operating load;
• and
• (b) deliver a control signal to said electrically controlled switch to open said switch after a delay interval following the time when the current drawn by the appliance falls below said threshold current level and during which the current drawn by the motor remains below the threshold current level;
• whereby energy consumption by the motor is reduced by removal of operating power when the motor is unloaded for an extended time.

A method for controlling an intermittently loaded electric appliance comprising:

• measuring the level of the idling current drawn by the appliance after the appliance is turned on but before the appliance is placed under an operating load;
• measuring the level of the current drawn by the appliance when under said operating load;
• establishing a threshold current level greater than the level of said idling current but less than the level of the current drawn by the appliance when under load;
• using a microcontroller, determining when the current drawn by the appliance has fallen below the said threshold current level after having reached a level of the current drawn by the appliance when under said operating load;
• and
• delivering from said microcontroller a control signal to an electrically controlled switch in series with a conductor arranged to deliver operating power to said appliance, to open said switch after a delay interval following the time when the current drawn by the appliance falls below said threshold current level and during which the current drawn by the appliance remains below the threshold current level;
• whereby energy consumption by the appliance is reduced by removal of operating power when the appliance is unloaded for an extended time.