5 pin relay wiring diagram
Learn the 5-pin relay wiring diagram with terminals 85, 86, 30, 87, and 87a. Step-by-step connection guide for automotive, lighting, and motor control systems.
Relay switch wiring diagram
A 5 pin relay has terminals 85 and 86 for coil, 30 as common, 87 as normally open (NO), and 87a as normally closed (NC), allowing dual circuit control.
Automatic water pump controller
The Fully Automatic Water Pump Controller Circuit is a must-have project for those homeowners and hobbyists who would like to have a fully automated water pumping system. This circuit is to make sure that the pump starts when there is a low level of water and automatically shuts off when the tank is full to avoid dry running.
This tutorial expounds on the mechanism of operation, the materials needed, the circuit diagram, and the construction of a fully automatic water pump controller step by step in a do-it-yourself manner. It also incorporates troubleshooting, safety measures, and home or farm water systems applications. The wide version of the circuit will allow you to save electricity, ensure that the pump is not damaged, and automate the everyday water management process, which does not require any human help.
Components Required for the Circuit
- Relay (12V DC or 230V AC based on pump)
- Float switches or water level sensors (low and high)
- Diode (1N4007 for relay protection)
- Transistor (BC547 or similar)
- Resistors (1kΩ – 10kΩ)
- Power supply (12V DC for control section)
- Water pump (AC or DC as required)
- Connecting wires, PCB, and enclosure
Working Principle of Water Pump Controller
Float Switch Operation
The low-level float switch detects an empty tank, while the high-level float switch senses when the tank is full. These switches send signals to the control circuit to automate the pump.
Relay Switching Mechanism
The relay receives control signals based on water levels. When the tank is low, the relay energizes to turn the pump ON. When full, the relay de-energizes, switching the pump OFF automatically.
Overload Protection
A diode protects the transistor from back EMF generated by the relay coil. An optional fuse can be added to protect the pump against overload or electrical faults.
Fully Automatic Water Pump Controller Circuit Diagram
- Connect the low-level float switch to the transistor base through a resistor.
- Connect the relay coil between the power supply and transistor collector.
- Place a diode across the relay coil for back-EMF protection.
- Connect the high-level float switch to provide the cut-off signal when the tank is full.
- Connect the water pump to the relay's normally open (NO) contacts.
- Ensure isolation between the control circuit power supply and pump power supply.
Step-by-Step DIY Construction Guide
- Mount the transistor, diode, and resistors on a PCB or breadboard.
- Connect float switches to the control input terminals.
- Attach relay coil and pump wiring to the correct terminals.
- Connect a stable 12V DC supply to the control section.
- Test switching manually using float switches before full deployment.
- Place the entire unit inside a waterproof or insulated enclosure.
- Adjust float switch heights for accurate water level detection.
Applications of Water Pump Controller Circuit
- Home water tank automation
- Farm irrigation systems
- Borewell and underground water pumping
- Fountains and water feature automation
- DIY smart water management projects
Safety Precautions
- Ensure AC pump wiring is fully insulated and isolated.
- Use a proper fuse or circuit breaker for the pump.
- Avoid touching live terminals while the pump is running.
- Secure float switches to prevent false triggers.
- Place the circuit inside a waterproof enclosure for long-term reliability.
Troubleshooting Common Issues
Pump Not Starting
Check the low-level float switch, verify transistor operation, and ensure the relay is receiving the correct signal.
Pump Running Continuously
Ensure the high-level float switch is properly positioned and verify that the relay is de-energising correctly when the tank is full.
Relay Not Switching
Check the orientation of the diode and confirm that the relay coil is receiving the correct voltage.
Frequently Asked Questions - 5 pin relay wiring diagram:
What is a 5 pin relay?
It is an electromechanical switch with 85, 86, 30, 87, and 87a terminals.
What is terminal 85 in relay?
It is one side of the coil, usually connected to ground.
What is terminal 86 in relay?
It is the other side of the coil, connected to positive or switch.
What is terminal 30 in relay?
It is the common input power terminal.
What is terminal 87 in relay?
It is the normally open (NO) output contact.
What is terminal 87a in relay?
It is the normally closed (NC) output contact.
What voltage does a 5 pin relay use?
Commonly 12V or 24V depending on design.
Where is 5 pin relay used?
In cars, lights, motors, and automation systems.
Can I use 5 pin relay as 4 pin?
Yes, just ignore the 87a terminal.
How to test a relay?
Apply voltage to coil (85–86) and check switching between 30, 87, and 87a with a multimeter.
