Applicable Systems
G3 Series
Symptoms
The HMI power supply voltage has dropped below the minimum 19.2V DC (for a 24V system). The display flickers and the HMI may reboot unexpectedly.
Possible Causes
- Power supply output voltage low due to overload or failure
- Wiring resistance too high from long cable runs or undersized conductors
- Loose terminal connection causing voltage drop under load
- Power supply filter capacitor degraded causing ripple and brownout
Troubleshooting Steps
- Step 1: Measure the voltage at the HMI power input terminals with a multimeter
Voltage should be 20.4-28.8V DC; if below 19.2V, investigate the supply - Step 2: Measure the voltage at the power supply output terminals
If the supply reads 24V but the HMI reads low, check the wiring for voltage drop - Step 3: Inspect all power wiring connections for tightness and corrosion
Tighten loose terminals and clean corroded contacts - Step 4: If the power supply is overloaded, check the total load against its rating
Add a dedicated supply or upgrade the capacity if overloaded
How to Reset
Reset: The HMI reboots automatically once the supply voltage is restored above 20.4V DC.
Common Replacement Parts
- Power supply: 24V DC, 50W, DIN-rail mount (Match output current to total HMI load)
- Power cable: 18 AWG, 2-core, shielded (Keep length under 30m to minimize voltage drop)
Frequently Asked Questions
- Q: What causes voltage drop in HMI wiring?
Long cable runs, undersized wire, and loose terminals. Calculate drop using V=2RLI/A where R is copper resistivity.
- Q: Can I use the PLC power supply for the HMI?
Only if the supply has sufficient spare capacity. A dedicated supply is preferred to isolate HMI noise from the PLC.
- Q: What is the HMI power consumption?
Typically 10-30W depending on screen size and backlight. Check the manual for the specific model.
Source: OEM Technical Manual
Category: HMI