Abstract: A thermostat or controller for controlling water circulation in a solar heating system is disclosed as including a resistant bridge circuit with a solar panel temperature responsive resistance and a storage tank temperature responsive resistance in opposite arms joined at one power input node with a differential comparator connected across the sensing nodes of the bridge. There are also disclosed optional features including additional fixed resistance divider circuits together with respective additional comparators sensing low-limit solar panel temperatures and/or high-limit storage tank temperatures for turning on or off the circulation pump, and/or for running cool water into the storage tank. In still another disclosed feature a sun switch produces periodic operation of the circulation pump to cause a sensor in the outlet of the solar panel to produce a true reading of solar panel temperature.

Abstract: A controller for a solar heating system includes a differential thermostat which responds to a preselected temperature differential between fluid in a solar collector and in a storage tank to operate a motor to pump fluid therebetween. The particular circuitry of the thermostat allows the use of non-linear sensing devices. Safety features includable in the controller provide for sensing of high and low extreme temperature conditions to prevent excess pressure in the storage tank or freezing of water in the collector.

Abstract: The invention is a time variable set point thermostatic device adapted for use in a two-wire circuit of a heating or cooling system without additional wiring. Electric timer means interconnected with a thermostatic switch and starting relay means of a transformer having a primary and secondary winding periodically changes the set point of the thermostatic switch at selected intervals. The circuit is arranged to limit the current in the two-wire control circuit to a value less than that required to actuate the starting relay of the heating or cooling system in the two-wire control circuit with the thermostatic switch open and to actuate the starting relay when the thermostatic switch is closed when the ambient temperature to be regulated varies a determined amount from a selected temperature set point and the thermostatic switch is closed.

Abstract: Energization of a motor is controlled by a latching relay operated by switch means passing current from a capacitor to the winding of the relay. The capacitor is charged through a relatively large impedance unipolarity input.

Abstract: A control circuit for a motor has an electronic RC timing circuit with a fluid pressure switch for shunting the timing circuit if the fluid pressure reaches and maintains a predetermined magnitude. The timing circuit terminates the energization of the motor when not shunted for a predetermined duration.

Abstract: A self-powered set-back electrical thermostatic device for use in a control circuit of a temperature control system requiring no additional wiring that includes a battery powered, motor driven timing mechanism for changing the ambient temperature setting of a thermostat at selected times.