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A servo press uses servo motors for precise force and position control during forming operations.

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Fanuc alarm 416 motor overheat - keeps tripping

sam_automation

Fanuc alarm 416 motor overheat keeps tripping on our press. We're not even running that hard. Ambient is 25°C. What's going on?

**Alarm 416 Definition
**
Fanuc alarm 416 is servo motor overheat. The motor thermistor has detected temperature above the threshold (typically 120-150°C depending on motor model).

**Immediate Actions
**
1. Stop production immediately
2. Do NOT restart until motor has cooled (minimum 30 minutes)
3. Check motor surface temperature with infrared thermometer
4. Check cooling fan operation

**Root Cause Analysis
**
#**Duty Cycle Too High**

The most common cause on servo presses: the motion profile demands too much continuous torque.

Check: Download drive data log and look at motor current over time. If current is consistently above 80% of rated, the motor is undersized or the cycle is too demanding.

Fix: Reduce SPM, add dwell time between strokes, or upgrade to larger motor.

**Cooling System Failure
**
- Check cooling fan on motor (should spin freely, no noise)
- Check air filter on drive cabinet (clean if blocked)
- Check ambient temperature in press area (should be below 40°C)
- For liquid-cooled motors: check coolant flow rate and temperature

#**Thermistor False Alarm**

If motor is cool to touch but alarm 416 triggers:
- Check thermistor resistance (should be 100-120 ohm at 25°C for most Fanuc motors)
- Check thermistor wiring for damage or loose connection
- Parameter 2165 controls thermistor alarm threshold — verify it has not been changed

**How to prevent this
**
Monitor motor temperature trend in the drive data. If temperature is rising session over session, address cooling before alarm occurs.

raj_pm

Check the cooling fan first. On Fanuc motors, the fan is a separate unit that can fail independently. We had a motor hitting overheat every 3 hours —fan motor had seized. $120 replacement fixed it. Also check that nothing is blocking airflow around the motor —I've seen rags and plastic wrap get sucked onto the fan intake.

anna_plc

If the motor is genuinely overheating (not a sensor issue), calculate your duty cycle. Fanuc motors are rated for specific duty cycles —typically S1 (continuous) or S3 (intermittent). If your actual duty cycle exceeds the rating, you need either a larger motor or a longer cooling period between cycles. Parameter 2086 sets the thermal time constant.

mchen_servo

Duty cycle is the one I see missed most often. Engineers size the motor for peak torque but don't check the RMS torque over a full cycle. On a servo press doing 40 SPM with a deep draw profile, the motor can be running at 90%+ RMS even if peak torque is within spec - and that's where the 416 alarm comes from after an hour of production. Quick check: pull the drive's torque monitor (on Fanuc that's in the servo check screen, parameter 3111 for torque reference). If you're seeing sustained values above 80% of rated, you need to either reduce cycle rate or look at the motion profile to reduce the high-torque dwell time at BDC.

carlos_mx

Coming back to this because we just dealt with a tricky 416 that wasn't any of the obvious causes.

Motor fan was fine. Duty cycle was fine (65% RMS). Ambient was 24C. Motor was still hitting 416 after about 90 minutes of production every time.

Turned out to be the motor's internal thermistor wiring. The thermistor connector at the motor junction box had corroded ??not enough to open-circuit (which would throw a different alarm), but enough to increase resistance by about 15%. Since the thermistor is a resistance-based temperature sensor, higher resistance = drive thinks the motor is hotter than it actually is.

We measured actual motor case temp with a contact thermocouple when the alarm fired: 78C. The drive was reading it as 135C. Cleaned the connector pins with DeoxIT, crimped new terminals, alarm went away permanently.

Diagnostic tip: if you suspect a false 416, compare the drive's reported motor temperature (parameter 2020 on Fanuc) against an external measurement. If there's more than a 10-15C discrepancy, you've got a sensor/wiring issue, not a real overheat.

Other sneaky cause we've seen: someone replaced the motor cooling fan with a "compatible" unit that spins the wrong direction. The fan housing looks symmetrical but the impeller is directional. Air was blowing OUT of the motor housing instead of pulling through it. Motor ran 30C hotter than it should have. Check airflow direction with a tissue paper strip at the exhaust port.