This control board is produced specifically for a domestic washing machine brand in China. It has been customized to meet the specific requirements and expectations of the customer in terms of product functionality and design. The design of the control board takes into account the desired appearance of the customer’s product. The customer is highly satisfied with the results, and we have received repeat orders from them six times already. This has helped the customer to expand their presence in the Chinese market significantly.

During this washing machine PCB controller projects, we learned the electrical components and principles is essential when designing a PCB controller for a drum-type fully automatic washing machine, that could help us to meet the functional requirements, safety standards, and performance expectations of a drum-type fully automatic washing machine.

Now, let’s take a quick look at the main components used in this project of a fully automatic drum-type washing machine and their operating principles.

Inlet Valve

The inlet valve is composed of an electromagnetic coil, housing, valve core, and mounting plate.

When a voltage of 220V, 50Hz is applied to the electromagnetic coil, it generates an electromagnetic field that attracts the valve core, opening the valve and allowing water to enter. When there is no voltage applied to the coil, the valve core, under the action of a spring, closes the valve, stopping the water flow.

The inlet valves can be classified into single-head, double-head, and multi-head types.

• Single-head inlet valves are used in regular drum washing machines.
• Double-head inlet valves are used in washing machines with drying functions (one valve is equipped with a flow restrictor for controlling the water supply during the drying process) or in drum washing machines with electronic water distribution.
• Multi-head solenoid valves are mainly used in drum washing machines that require hot water inlet, have drying functions, or adopt electronic water distribution.

Water Level Switch

There are two types of water level switches: mechanical water level switches and electronic water level switches.

Mechanical water level switches change their state based on the variation of air inside an internal air bladder. When water enters the washing machine, the air inside the connected hose of the water level switch gets sealed and compressed. As the water level rises, the air inside the hose gets further compressed, increasing the pressure. Once it reaches a certain value, the normally closed contact of the water level switch is pushed open, and the normally open contact is closed, cutting off the water supply. The washing machine then automatically enters the washing program. When the water level decreases, such as during drainage, the decreased pressure in the sealed air causes the normally closed contact to reconnect, while the normally open contact opens.

Washing machines that use mechanical programmable controllers and integrated electromechanical programmable controllers utilize mechanical water level switches.

Fully computer-controlled washing machines employ electronic water level switches. As the water level rises, the water level switch generates pulses at a specific frequency. The microcontroller amplifies and processes these pulses to determine whether the current water level has reached the set level. If the set water level is reached, the machine proceeds to the next operation.

Electric Motor

Drum washing machines use two types of motors: dual-speed motors and series-excited motors.

Dual-speed motor is a single-phase capacitor-operated induction motor. It consists of a 16-pole low-speed winding and a 2-pole high-speed winding assembled on the stator. During the wash cycle, the 16-pole winding is used, providing low speed but high torque. During the spin cycle, the 2-pole winding is used, providing high speed but low torque. Dual-speed motors have excellent starting characteristics (high starting torque) and operational performance (strong overload capacity).

Series-excited motor adopts a commutator structure and belongs to a motor that can operate on both AC and DC power. It is called a series-excited motor because the excitation winding on the stator core and the armature winding on the rotor are connected in series. Series-excited motors can easily achieve stepless speed control through a certain control circuit, making the machine’s operation smoother. Series-excited motors have advantages such as high torque, strong overload capacity, high speed, small size, light weight, and convenient speed control.

Both types of motors are equipped with overheating protection devices. When the motor experiences a locked-rotor condition and the temperature of the motor windings rises to a certain value, the thermal protector automatically disconnects the circuit, protecting the motor. When the winding temperature decreases, the thermal protector reconnects the circuit.

Figure 1 shows the wiring diagram of the dual-speed motor: M3 and M7 form the 16-pole winding. M2 and M6 form the 2-pole winding. TP represents the temperature protector.

Figure 2 shows the wiring diagram of the series-excited motor: D5 and D10 form the stator winding. D8 and D9 form the rotor winding. TP represents the temperature protector.

Heater

To enhance the washing effect of the washing machine, a heating function is usually employed in a drum-type washing machine.The outer wall of the heater is made of stainless steel tubing, with a heating wire placed at the center and insulated with magnesium powder in between.

• The power of the electric heating tube for washing is 1700W, installed at the lower part of the outer drum, with the heating section immersed in water.
• The power of the electric heating tube for drying is 1200W (or 1000W), installed on the air duct of the outer drum. Due to the variation in stainless steel materials, this heating tube can withstand high temperatures and be used for dry burning. During the drying process, the drying fan blows the heat generated by the heating tube into the washing machine, removing moisture from the clothes.

Temperature Controller and Thermostat

Many drum-type washing machines have a heating function, which requires temperature control and selection using a temperature controller or thermostat.

• A thermostat is a temperature controller with a fixed temperature value. It is a type of bimetallic expansion thermostat that operates by utilizing the deformation of bimetallic strips when heated, thereby activating the contacts.
• A temperature controller is a linearly adjustable liquid expansion thermostat. It operates by utilizing the expansion of liquid within the temperature sensor when heated, thereby driving the actuator to control the operation of the heating tube.

If a washing machine adopts a mechanical program controller, a temperature controller and thermostat are always required whenever heating is involved.If a washing machine is controlled by a computer board, the heating temperature is fed back to the microcontroller on the control board through a temperature sensor. The microcontroller then controls the operation of the heating tube based on program requirements.

Electric Door Lock

The electric door lock is fixed inside the enclosure on the right side of the front door of the washing machine, and its lead wires are connected in the power circuit. When the washing machine door is closed and the power is turned on, the PTC heating element inside the door lock starts to heat up, connecting the main circuit and simultaneously engaging the “door lock tongue” to securely lock the washing machine door, preventing any danger of the door being opened during operation.When the power is turned off, the PTC heating element begins to cool down until it transitions from the high-resistance state to the low-resistance state (this process generally takes 1.5 to 2 minutes). At this point, the “door lock tongue” springs back, and the door can be opened.

Piano Key Switch

The piano key switch is a functional switch that is installed on the control panel to select various functions of the washing machine, such as power on/off, economy wash, wrinkle-free, high-temperature wash, no spin, and more.

Drain Pump

Most drum washing machines use a top drainage method for draining, therefore a drain pump is used for the drainage process.

Electronic Speed Control Board

The electronic speed control board, when paired with a series-excited motor, enables stepless speed control.

Drying Timer

The drying timer is used to set the drying time for clothes. It is driven by a synchronous motor and operates through a gear reduction mechanism, which rotates two cam discs to control the action of two sets of contacts: A-A1 (controls power supply to the drying system) and B-B1 (low-temperature drying).

Currently, our company uses a drying timer with two working time segments: 0-120 minutes and 0-80 minutes.

• When the timer is set to 0-120 minutes, both sets of contacts operate simultaneously, causing the motor and heater to work together for drying and heating.
• When there are 12 minutes remaining in the set time, the timer cuts off the B-B1 contact to initiate low-temperature drying.When the timer is set to 0-80 minutes, the A-A1 contact operates while the B-B1 contact does not, and the system performs only low-temperature drying.

Filter

To prevent electromagnetic interference from the washing machine affecting other household appliances through the power network, a filter should be installed in the power circuit of the drum washing machine. The filter consists of resistors and capacitors, forming a filtering network (as shown in the diagram). It is designed to absorb the multiple harmonics generated during the operation of the washing machine and redirect them to the ground via the ground wire, thereby avoiding interference from harmonics on other appliances.

Now, do you feel more confident about designing a control board for a fully automatic drum-type washing machine? Don’t worry, SuperPCBA is here to help you complete your customized control board manufacturing. Our commitment to efficiency, speed, and competitive pricing remains unchanged. We welcome both new and existing customers to inquire and negotiate with us！