This is a swimming pool solar heating panel pump control. The circuit in below is use an external thermistor that is attached to the solar panel in a manner that will allow it to sense heat generated by direct exposure to the sun. This circuit is controlled by IC TC621-C. This is the figure of the circuit.
A thermistor with a resistance of about 100 kΩ at 25°C should be selected. One such thermistor is the ACW-027 from Ketema, which can be clamped around a pipe in the solar panel. This circuit will energize the pump when the sun is heating the panels and turn off the pump when the sky is cloudy or the sun goes down. To prevent rapid cycling of the pump during partly cloudy conditions, the hysteresis is set for a relatively wide (20°F) span. Providing low thermal impedance between the thermistor assembly and the solar panel will also prevent rapid pump cycling by adding the solar panel’s thermal time constant to the hysteresis. To select the set point resistors, consult the thermistor data sheet for the thermistor’s value at the desired temperature. For example, assume that we want the pump to turn on (high set point) at 100°F and turn off (low set point) at 80°F. [Schematic diagram source: Microchip Technology, Inc].
A thermistor with a resistance of about 100 kΩ at 25°C should be selected. One such thermistor is the ACW-027 from Ketema, which can be clamped around a pipe in the solar panel. This circuit will energize the pump when the sun is heating the panels and turn off the pump when the sky is cloudy or the sun goes down. To prevent rapid cycling of the pump during partly cloudy conditions, the hysteresis is set for a relatively wide (20°F) span. Providing low thermal impedance between the thermistor assembly and the solar panel will also prevent rapid pump cycling by adding the solar panel’s thermal time constant to the hysteresis. To select the set point resistors, consult the thermistor data sheet for the thermistor’s value at the desired temperature. For example, assume that we want the pump to turn on (high set point) at 100°F and turn off (low set point) at 80°F. [Schematic diagram source: Microchip Technology, Inc].
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