Two-wire water level controller production

Two-wire water level controller production

Here we introduce a two-wire water level controller. The circuit uses only 10 components and can be directly welded on a small circuit board (can be directly welded under amateur conditions). Together with two reed switches used for water level detection, it is encapsulated in a stainless steel tube. Although this controller is small in size, it has a large driving power. It can not only directly drive AC contactors of various powers of 220V~380V, but also eliminate the AC contactor and directly drive single-phase AC motors with a power of less than 400W. Since only two wires are connected in series in the load circuit, the peripheral connection is simplified to the maximum extent, making the overall structure very simple. It is easy to install, easy to use, no debugging is required, the power consumption is very small, and almost no power is consumed when unloaded. In addition, according to needs, an external control switch can be connected to convert the three different working states of "automatic water supply-stop water supply-manual water supply", which is more flexible and convenient to use.

How it works

The figure above is a circuit schematic. The dotted box in the figure is the control circuit, and 10 components are installed on a small circuit board; K1 and K2 are two reed switches, installed at both ends of a stainless steel pipe of appropriate length, and cooperate with a float equipped with a permanent magnet to form a float-type water level detection device to detect the upper and lower water levels respectively; K3 is the working state control switch, which is divided into three working states: "automatic water filling", "stop water filling", and "manual water filling"; J is an AC contactor, which can also be a water filling solenoid valve or a low-power water filling motor.

The following figure is a schematic diagram of the structure of a two-wire water level controller. The control circuit and two detection switches are encapsulated in a stainless steel tube with both ends closed. Outside the stainless steel tube is a float that can move up and down and is equipped with a permanent magnet and two water level stops that limit the range of the float's movement, which are connected to the periphery with only two leads.

Now take J using AC contactor as an example to explain the working process. When K3 is placed in the "automatic" position, the AC 220V power supply passes through the coil of J1, and is rectified by D1~D4 bridge to output DC voltage, which is divided by R1 and R3. There is about ten volts of DC voltage on C1 as the trigger voltage of the thyristor control.

When the water level in the water tank is lower than the lower water level detection reed switch K2, the permanent magnet in the float makes the lower water level detection reed switch close and turn on. The voltage on C1 is supplied to the trigger voltage of the thyristor V1 trigger terminal through R2. At this time, V1 is turned on, the AC contactor J is attracted by the working voltage, and the contact of J provides the working power supply for the water pump motor for water supply, and the water level in the water tank begins to rise; as the water level rises, the float leaves the lower water level reed switch, K2 is disconnected, but V1 remains in the on state. This is because after V1 is turned on, the resistance of R2 is very small, and there is leakage current charging C1 through the anode and gate of V1 through R2, so that the two ends of C1 still maintain a certain voltage, which also maintains the conduction state of V1 unchanged, and the water pump continues to work; when the water level reaches the upper water level detection switch K1, the permanent magnet in the float makes the upper water level detection reed switch close and turn on, the thyristor trigger terminal is zero, the voltage on C1 drops to zero, V1 is cut off, the AC contactor J loses the working voltage and disconnects, and the water pump motor stops working. Even if the water level drops and the float leaves K1, V1 remains disconnected until the next working cycle begins, thus achieving automatic control of the water level.

J can also be a water supply solenoid valve, which is opened or closed by the controller; it can also be a low-power AC motor, which is directly controlled by the controller to control the water pump to supply water/stop supplying water.

If necessary, a three-position switch K3 can be added to set different working states of the water supply pump motor. When the automatic control part fails or water supply is required at any time, it can meet the needs.

Equipment selection

The thyristor V1 should use a micro trigger current, such as 2P4M parameters: Vdrm: 400V, Ir: 2A, Igt: 0.2mA, T0220A package. When the driving power is not large, it can be replaced by 2N6565 in T092 package to reduce the size. 2N6565 parameters: Vdrm:

400V, Ir: 0.51A, Igt: 0.35mA. When using 380V AC contactor, 2P6M can be used, Vdrm: 600V. The diode should also be selected according to the driving power. When using 220V or 380V AC contactor and low power, 1N4007 is used. When directly driving the motor or high-power drive output, 1N5404 or 1 N5407 is selected. The pipe should be made of non-magnetic materials such as stainless steel pipe. The length is determined according to the depth of the water tank or the water level difference to be controlled. It is best to use stainless steel pipe. PVC material is also acceptable, but the strength and service life are worse. The inner diameter of the pipe is between φ18 and φ25 mm, which is determined by the size of the circuit board. Due to the small number of components, the circuit board can actually be made very small. 2 or 4 pairs of permanent magnets are installed in the float, with opposite polarities close to the steel pipe surface and firmly bonded. The float material is made of finished spherical stainless steel float or non-absorbent foamed plastic.

A few points to note
1. The power wiring direction is as shown in Figure 1. Since the circuit directly uses 220V or 380V without isolation, the phase line should be connected to one end of the contactor at 220V, and attention should be paid to insulation treatment.

2. When connecting the motor, there must be fuse protection to prevent the motor from overloading or overcurrent and damaging the controller.

3. Ensure that both ends of the stainless steel pipe are water-proof and water-tight. The circuit board must be insulated to prevent leakage.

4. All types of reed switches can be used, but they must be properly fixed and protected to prevent vibration and breakage.