When reading and explaining relay wiring diagrams, it is first necessary to understand the components of the relay and the roles of each component in the circuit. Below, I will guide you step by step to understand the relay wiring diagram and use specific examples to illustrate it
1. Identify relay coils
- Find the symbol representing the relay coil in the wiring diagram.
- The coil terminals are usually marked as 85 and 86, which are the positions where the control voltage is connected.
- When voltage is applied to these two terminals, the coil will be energized and activate the relay.
2. Find the contact point
Identify the normally open (NO), normally closed (NC), and common terminal (COM) contacts of the relay:
- COM： Usually marked as 30.
- NO： Mark as 87, disconnect when the relay is not activated.
- NC： Marked as 87a, connect to COM when the relay is not activated.
3. Track the circuit path
Starting from the power supply:
1. Observe how the current flows through the relay coil.
2. Analyze how the control signal activates the relay.
View load control:
- Track from COM terminal to NO or NC contact.
- Understand how relays control loads (such as lights) by switching contacts.
4.Check additional components
Diode protection (if any):
- If the wiring diagram includes diodes, check their polarity.
- The cathode (usually marked with a line) should be connected to the positive voltage terminal to prevent the reverse voltage spike generated by the inductor from damaging the control circuit.
Example analysis: Automotive headlight control
The following is a typical 4-pin relay wiring diagram for controlling car headlights:
- Terminal 85: Connect the ground wire.
- Terminal 86: Connect the headlight switch and connect it to the positive terminal of the battery when pressed.
- Terminal 30: Connect the positive terminal of the battery to provide power to the load.
- Terminal 87: Connect the positive pole of the headlight.
working principle
1.When the headlight switch is pressed, voltage is applied between 85 and 86, and the coil is energized.
2.After the coil is powered on, the relay switches internally and connects COM (30) to NO (87).
3. Current flows from the battery through the relay to the headlights, causing them to light up.
By following the above steps, one can clearly interpret the relay wiring diagram and understand its role and working mode in the circuit.
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