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My Actuator Stops or Stalls Under Load — How Do I Fix It?

An actuator that runs freely with no load but stalls or cuts out when the mechanism is attached usually indicates an overload, thermal protection trip, or insufficient power supply. Here's how to diagnose it.

Why Actuators Stall Under Load

  • Load exceeds rated capacity— The actuator is being asked to push or pull more than its dynamic load rating allows. Running at over 100% load causes immediate stall.
  • Thermal cut-out triggered— If the actuator has been running near full load, the motor thermal protector may trip. The actuator will restart once cooled (typically 5–15 min).
  • Power supply voltage sag— Under-rated PSUs can't maintain voltage when the actuator draws peak current. Voltage sags, speed drops, and the internal protection may cut out.
  • Duty cycle exceeded— Running beyond the rated duty cycle heats the motor. Thermal protection trips even at rated load if run continuously past the allowed on-time.
  • Side-loading friction— Off-axis forces create extra mechanical resistance, increasing effective load even if the axial load is within spec.

Diagnostic Checklist

  • Verify the actual load against the actuator's dynamic force rating (see datasheet onPA Resources page)
  • Use a clamp meter to measure current draw under load — compare to rated running current
  • Measure supply voltage at the actuator terminals under load — must be within 0.5 V of rated voltage
  • Check operating duty cycle — if actuator has run > 25% of time in last 10 min, allow it to cool
  • Check mounting for binding, side-loading, or off-axis forces
  • Try a different power supply of higher current rating as a test

💡  Use the PA Force Calculator — Input your load, angle, and geometry at the PA Force Calculator to verify you have selected an actuator with sufficient rated capacity for your application.