Detailed Structure of a Relay on an Electric Forklift Controller

What is a relay?

A relay is an electrically operated switch that allows the controller to use a small control current to switch large load currents (contactors, solenoid valves, auxiliary motors, etc.).

👉 In electric forklifts, relays are commonly used to:

• Control the main contactor

• Activate the electric brake

• Control pumps, valves, and auxiliary circuits

• Isolate logic circuits (5V / 12V) from power circuits

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Common Types of Relays Used on Forklift Controller Boards

• 12VDC relays

• 24VDC relays

• PCB-mounted relays (plastic case relays)

• Intermediate relays (mini relays)

📌 Relays cannot replace contactors
→ Relays only provide control signals; contactors handle the high motor current

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Detailed Structure of an Electromechanical Relay

1️⃣ Coil

Structure

• Copper wire wound around an iron core

• Rated voltage: 12V / 24V DC

Function

• When energized → generates a magnetic field

• Pulls the movable iron core → actuates the contacts

📌 Coil failure symptoms

• No “click” sound

• Relay does not pull in despite control signal

• Coil measured as open or short circuit

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2️⃣ Fixed Core & Moving Armature

Structure

• Fixed iron core

• Movable armature connected to a lever

Function

• Pulled in when the coil is energized

• Transfers mechanical force to the contacts

📌 Common issues

• Sticking due to dust or rust

• Weak pull-in → relay does not switch firmly

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3️⃣ Return Spring

Function

• Returns the armature to its original position when power is removed

• Ensures fast contact release

📌 Weak spring

• Slow relay release

• Contacts are more likely to burn

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4️⃣ Contacts

Types of contacts

• NO (Normally Open)

• NC (Normally Closed)

• COM (Common terminal)

Function

• Switches load circuits (contactors, valves, auxiliary circuits)

📌 Most common failures

• Burnt contacts

• Welded (stuck) contacts

• Poor contact → voltage drop

👉 Relay clicks but the circuit does not operate = 80% chance of burnt contacts

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5️⃣ Relay Housing

Function

• Protects internal components

• Provides electrical insulation

• Limited dust protection

📌 In humid environments, forklift relays are prone to oxidation

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Basic Relay Working Principle

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Role of Relays in Forklift Controller Boards

• Relays act as an intermediate interface

• Logic board (5V / 12V) → relay → contactor → motor

• Protects the MCU from handling high current

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Signs of a Faulty Relay on a Forklift Controller

• No “click” sound when the key is turned on

• Forklift has power but does not move

• Contactor does not engage

• Electric brake does not release

• Intermittent operation