Sump Pump Run-Time Limiter Circuit: Overview
This circuit was designed to prevent sump pump damage caused by extended operation in a dry sump. Its function is to monitor the pump’s running time and, if it surpasses a predetermined limit (set at 30 minutes in this case), cut off the power supply to the pump to prevent potential damage.
Circuit Configuration and Pump Connection
The protector circuit is integrated into the mains supply cable of the pump, effectively breaking the circuit if the pump runs for an excessive duration. The schematic diagram illustrates three key components: the power supply, the timing circuit, and the in-use detector. The 230-V input is on the left, and the output is on the right. The power supply draws voltage directly from the mains connection through transformer Tr1. Stabilization is unnecessary, allowing for a standard configuration involving a transformer, a bridge rectifier, and a smoothing capacitor. An indicator LED (D5) serves as an on/off signal for the circuit’s status.
Timing Function and Output Control
For the timing function, a 4060 (IC1) is employed. LED D10 (Count) serves as a visual indicator, blinking while power is supplied to the load. After 30 minutes, output Q14 of IC1 goes high, interrupting power to the load. Alternatively, the Test jumper position allows the selection of output Q6, which cuts off power to the pump after 6 seconds for testing purposes.
Pump Running Detection and Timing Control
Two anti-parallel diodes (D6–D7) are placed in series with one of the supply leads to detect the pump’s operation. When the pump activates, the voltage drop across these diodes triggers conduction in T1 and T2. These transistors pull down the Reset input of IC1, initiating the timing sequence. Diodes D8 and D9 create a return path to ground from the Reset pin, preventing a direct connection that would short out the detection diodes. This configuration keeps the Reset level around 0.8 V. Capacitor C2 suppresses crossover spikes from the AC signal, preventing circuit malfunctions.
Relay Activation and Restart Function
If the pump continues running beyond the set interval, T3 energizes the 12-V relay Re1. Re1, in turn, activates a 220-V relay with two changeover contacts. One contact interrupts the supply voltage to the pump, while the other activates the Reset LED (D11). To restart the pump, the Restart button must be pressed.
Practical Considerations and Safety Precautions
When implementing this circuit, a Eurocard relay can be used for Re1, and the Reset pushbutton switch should be a normally closed 230-V type. Due to the circuit’s connection to the mains network, prioritizing electrical safety during construction is crucial. Using a well-insulated enclosure is mandatory to ensure user safety.