Pro
12 min
Wiring 4 — Digital Output to Relay / Contactor
wiringdigital-outputrelayflyback-diode
Ready to build this?
Sign up free — no credit card required. This scenario requires the Pro plan.
Sign up to play this scenario →Already have an account? Log in
Briefing
A PLC output module can switch a 24 VDC relay coil ON and OFF. When the coil is de-energised, the collapsing magnetic field creates a **flyback voltage spike**. A **freewheeling diode** (flyback diode) across the coil clamps the spike and protects the PLC output transistor. Wire the relay coil and its flyback protection to the PLC output %Q0.0.
Objectives
- Wire relay coil A1 (+) terminal to PLC output %Q0.0
- Wire relay coil A2 (−) terminal to 0 V common
- Wire the flyback diode anode to 0 V, cathode across coil to %Q0.0
Hints
- Relay coil A1 connects to the PLC output; A2 to 0 V. Never reverse them.
- The flyback diode must face AGAINST the supply voltage: cathode (+) toward +24 V / %Q0.0.
I/O Table
Outputs
RELAY_A1Relay coil A1 (+) — connect to PLC output
BOOL · %Q0.0
RELAY_A2Relay coil A2 (−) — connect to 0 V bus
BOOL · %Q0.1
DIODE_KFlyback diode cathode — connect to PLC output side
BOOL · %Q0.2
Related scenarios
Ready to build this?
Sign up free — no credit card required. This scenario requires the Pro plan.
Sign up to play this scenario →Already have an account? Log in