PLC resets or memory loss typically show up as:
Program disappearing after power cycle
Machine returning to factory defaults
Random restarts during production
Time/date resetting
I/O mapping lost
Unexpected fault messages
This is almost never a “software bug.”
It is almost always power or hardware related.
Most PLCs use an internal battery to:
Retain program memory
Preserve parameters
Maintain clock and data
If battery fails:
Program may erase after shutdown
Time/date resets
Parameters disappear
✔ Look for “Low Battery” warning
✔ Check battery replacement interval
✔ Replace with manufacturer-specified battery
Never ignore battery warning alarms.
PLC power supply instability can cause:
Random resets
Memory corruption
Partial boot failures
Voltage drops
Phase imbalance
Loose wiring
Overloaded control transformer
✔ Measure 24V DC stability
✔ Inspect power supply terminals
✔ Check incoming AC voltage under load
✔ Verify proper grounding
PLC requires stable, clean voltage.
If the 24V power supply is:
Undersized
Overloaded
Aging
It may drop voltage during high demand (solenoids, relays switching).
PLC resets when hydraulic solenoids activate
Reset during punch or shear cycle
✔ Measure voltage during peak load
✔ Upgrade to properly sized power supply
✔ Separate PLC power from heavy solenoid loads
Control voltage must be isolated from high-current devices.
High-frequency noise from:
VFDs
Motors
Large solenoids
Can cause:
PLC communication faults
Unexpected resets
Data corruption
✔ Ensure proper grounding
✔ Separate signal and power cables
✔ Use shielded cables
✔ Install ferrite cores if necessary
Noise is a common hidden cause of instability.
PLC memory can degrade over many years.
Especially if:
Frequent program downloads
Power interruptions during writes
Poor shutdown practices
Random loss of specific parameters
Program partially corrupted
✔ Reload clean backup
✔ Update firmware
✔ Replace PLC if memory chip failing
Always keep a verified backup copy.
In modular PLC systems:
I/O cards may loosen from vibration
Backplane connection may be unstable
Intermittent resets
Communication errors
Partial I/O loss
✔ Power down safely
✔ Reseat modules
✔ Inspect connectors
Vibration is common in roll forming environments.
If power is cut abruptly during:
Data write
Parameter change
Firmware update
Memory may corrupt.
Use proper shutdown process whenever possible.
Excess heat inside electrical cabinet can:
Cause PLC reboot
Shorten battery life
Corrupt memory
✔ Cabinet fans
✔ Air filters
✔ Ambient temperature
✔ Dust buildup
Control systems need clean airflow.
Improper grounding can cause:
Floating voltage
Noise feedback
PLC instability
✔ Solid earth grounding
✔ No ground loops
✔ Clean bonding between panels
Grounding is critical for PLC reliability.
| Symptom | Likely Cause |
|---|---|
| Loses program after power off | Backup battery dead |
| Resets during punching | 24V voltage drop |
| Random resets at high speed | Electrical noise |
| Date/time always resets | Battery failure |
| Resets after long run | Overheating |
Understanding the pattern dramatically narrows the cause.
If PLC is resetting:
Check for battery alarm
Replace battery proactively
Measure 24V under load
Check grounding integrity
Inspect cabinet cooling
Review VFD and motor cable routing
Reload clean backup program
Monitor system over multiple runs
Never operate without a verified program backup.
PLC resets can cause:
Punch misfires
Shear misalignment
Unexpected machine motion
Production downtime
Parameter loss
Control stability is critical for safe operation.
PLC memory loss or resets are usually caused by:
✔ Dead backup battery
✔ Power supply instability
✔ 24V voltage drop
✔ Electrical noise
✔ Overheating
✔ Loose I/O modules
✔ Corrupt memory
The most common cause is a failing backup battery combined with unstable control voltage.
A stable roll forming machine requires:
Clean power → Stable 24V supply → Good grounding → Proper cooling → Regular battery replacement.
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