Share an oil sump/fill pump controller circuit

Pump controller circuits are very important for efficient management of water. Implementing automatic filling pumps and sump pumps based on the availability of water in the tank or sump is the best way to manage it efficiently. Here, we will do something similar by automating the sump pump and automatically draining the water once the sump is full. This circuit can be used in underground rainwater collection tanks or sewer systems. Moreover, this pump controller circuit can be customized as a normal water level controller for water tanks or reservoirs.

Working operation of sewage pump controller:

Refer to Figure 1 (schematic) for this discussion. The heart of the oscillator is U1A, R1-R5, and C1. R1 and R3 split the V1 supply voltage in half, and their combined resistance is R1*R3/(R1+R3) = 50K. Since R2 = 100K, when the output of U1A switches from ground to 15 volts (+V1), the junction of U1A+ and R1, R2, R3 switches from 4 volts to 8 volts. R5 begins to charge C1. When C1 charges above 8 volts, the input of U1A- is higher than U1A+. This causes the output of U1A to switch to 0 volts. In turn, the junction of U1A+ and R1, R2, R3 switches from 8 volts to 4 volts. R5 begins to discharge C1. When C1 discharges below 4 volts, the input of U1A- is lower than U1A+. The output of U1A switches from 0V to 12V (+V1), and the junction of U1A+ and R1, R2, R3 switches from 4V to 8V. R5 starts charging C1, and the cycle repeats. C1 keeps going up and down between +V1*1/3 (4V) and +V1*2/3 (8V). What's really cool is that this circuit oscillates at the same frequency even as the supply voltage +V1 changes!

The output of U1A is a 12 volt square wave with a frequency of about 400 Hz. The output is connected to C2 and C5, which power one side of the electrode pair to detect low and high levels of water. The electrodes can be adjusted to provide any lower and higher levels desired by the user. S1 and S2 represent only two electrode pairs. C2 and C3 are connected to the lower level electrode pair, while C5 and C6 are connected to the higher level electrode pair. C3 is connected to D1, D2, C4, R6, forming a charge pump connected to the U1B+ input. If the water is below the low level electrode, no oscillating current flows through C3 and the charge pump turns off. R6 discharges C4, so the output voltage of U1B+ is zero, which is lower than the 8.9 volt reference of U1B- provided by R5 and R4.

Therefore, the output of U1B is zero, lighting LED, D5 (green), indicating low level in the tank. When the tank level rises above the low level electrode, an oscillating current flows through the water to C3. C3 passes an AC current through D1 and D2, pumping a charge onto C4. When the C4 charge voltage exceeds 5.4 volts, the output of U1B switches from low to high. This turns off LED D5 (low) and turns on LED D6 (yellow, medium) because the high charge pump is off and U1C output is low. While the output of U1B is high, the positive feedback through R15 and the low output of U14C coupled through R1 sets the input of U1D+ to approximately 3 volts. Since the input of U1D+ is less than the 5.4 reference voltage, the output of U1D is low and the sump pump remains off.

If you examine the charge pump formed by C3, D4, D7, C7, R1 connected to the input of U6C+, you will see that it works exactly the same way as the low level circuit. So when water connects the high level C5, C6 electrode pair, C7 charges above the 5.4 reference voltage and the output of U1C goes high. This causes two things to happen. First, LED D6 (mid level) turns off and LED D7 (red, high level) turns on. Second, because both U1B and U1C are high, R13 and R14 pull the input of U1D+ to 6.2 volts, which is above the 5.4 reference voltage. The output of U1D switches high. This turns on Q16 through resistor R1 and energizes relay RLY1.

This turns the sump pump on and lights the pump on LED D8 (green). While the pump is on, the water level in the tank drops. When the high C5, C6 electrode pair is dry, the D3, D4 charge pump turns off (zeroed), U1C+ falls below the reference voltage, the U1C output goes low, and LED D7 (red, high) turns off. Since the U1B output is still high, LED D6 (yellow, mid) turns on. Since U1D is high and U1B is high, the voltage input to U1D+ (about 7.5 volts) keeps the pump on. When the water drops below the low electrode, the low level charge pump goes to zero and the output of U1B also goes to zero. When this happens, R13 and R14 are zero, resulting in a U1D input voltage of about 4.4 volts, which causes the output of U1D to switch low, turning the sump pump off.

Changing a Sump Pump to a Fill Pump Controller Circuit:

Let's say you want to use this circuit to fill the tank when it gets low. Simply invert the inputs to U1B and U1C. That is, connect the charge pump to the U1B and U1C- inputs, and connect the U1B+ and U1C+ inputs to the R8, R9 reference voltage. Notice that LED D7 will represent a low tank, and LED D5 will now represent a full tank. Now, when the tank is full, U1B and U1C will be low and turn off the fill pump. When the tank drops below the low level, U1B and U1C will raise and turn on the pump to fill the tank.

The best part of this circuit is that it uses an alternating current on the electrodes to prevent them from corroding or forming scale which can degrade them and cause them to stop working. This means greater reliability and longer life.