I. Working Principle of Electromagnetic Relays
An electromagnetic relay is an electromechanical component that uses an input signal (voltage or current) to generate electromagnetic force in the core of an electromagnet, attracting an armature and thus actuating the contacts to open, close, or switch control. Electromagnetic relays are widely used in aviation, aerospace, shipbuilding, and home appliances, primarily performing functions such as signal transmission, execution control, and system power distribution. They are one of the key electronic components in various systems.
An electromagnetic relay is a switch that uses an electromagnet to control the on/off state of a working circuit.
(1) Structure: The main components of an electromagnetic relay are electromagnet A, armature B, spring C, moving contact D, and stationary contact E.
(2) The working circuit can be divided into two parts: low-voltage control circuit and high-voltage working circuit. The low-voltage control circuit includes electromagnetic relay coil (electromagnet A), low-voltage power supply E1, and switch S; the high-voltage working circuit includes high-voltage power supply E2, motor M, and electromagnetic relay contacts D and E.
(3) Working principle: When the switch S in the low-voltage control circuit is closed, the current passes through the coil of the electromagnet A to generate a magnetic field, which in turn attracts the armature B, causing the moving and stationary contacts D and E to come into contact, the working circuit is closed, and the motor works; when the low-voltage switch S is opened, the current in the coil disappears, and the armature B, under the action of the spring C, causes the moving and stationary contacts D and E to separate, the working circuit is opened, and the motor stops working.
When a certain voltage is applied across the coil, a certain current flows through it, generating an electromagnetic effect. The armature, attracted by this electromagnetic force, overcomes the pull of the return spring and is drawn towards the iron core, causing the moving contact of the armature to engage with the stationary contact (normally open contact). When the coil is de-energized, the electromagnetic attraction disappears, and the armature returns to its original position under the spring's reaction force, releasing the moving contact from the original stationary contact (normally closed contact). This engagement and disengagement achieves the purpose of connecting and disconnecting the circuit. The normally open and normally closed contacts of a relay can be distinguished as follows: the stationary contact that is in the open state when the relay coil is not energized is called a "normally open contact"; the stationary contact that is in the closed state is called a "normally closed contact."
II. Wiring Instructions for Electromagnetic Relays
Electromagnetic relays generally consist of an electromagnet, armature, spring, and contacts. Their operating circuit comprises a low-voltage control circuit and a high-voltage operating circuit. Electromagnetic relays can also achieve remote and automated control. When a certain voltage is applied across the coil, a current flows through it, generating an electromagnetic effect. The armature, attracted by the electromagnetic force, overcomes the return spring's pull and is drawn towards the core, causing the moving contact to engage with the stationary contact (normally open contact). When the coil is de-energized, the electromagnetic attraction disappears, and the armature returns to its original position under the spring's reaction force, releasing the moving contact from the original stationary contact (normally closed contact). This engagement and disengagement achieves the purpose of connecting and disconnecting the circuit. The "normally open" and "normally closed" contacts of a relay can be distinguished as follows: the stationary contact that is open when the relay coil is not energized is called a "normally open contact"; the stationary contact that is closed when the relay coil is energized is called a "normally closed contact."
III. Selection of Relays
1. First, understand the necessary conditions: ① The power supply voltage and maximum current that the control circuit can provide; ② The voltage and current in the controlled circuit; ③ The number and type of contacts required by the controlled circuit. When selecting a relay, the power supply voltage of the control circuit can generally be used as the basis for selection. The control circuit should be able to provide sufficient operating current to the relay; otherwise, the relay's operation will be unstable.
2. After determining the usage conditions by consulting relevant materials, find the required relay model and specification number. If you already have a relay, check its usability against the available information. Finally, consider whether the size is suitable.
3. Pay attention to the size of the appliance. For general electrical appliances, in addition to considering the chassis size, the main consideration for small relays is the circuit board mounting layout. For small electrical appliances, such as toys and remote control devices, ultra-miniature relays should be selected.
