The Allen-Bradley AC Servo 1391 series is a family of AC servo controllers. To maintain the UL listing, the power to an AC Servo 1391 controller must be provided from an Allen-Bradley 1391 Isolation Transformer. Only users trained on 1391 servo controllers and associated equipment should be involved in the planning and implementation of this controller system. Furthermore, static control procedures should be followed to minimize the probability of component damage. The AC Servo 1391 controllers are PWM (Pulse Width Modulated) servo controllers which are dedicated, single-AC-axis AC servo controllers. They are typically used along with computer-aided closed-loop positioning systems to control the position and rotary or linear motion of machine parts on an automated machine. AC Servo 1391 controllers are designed for panel mounting inside an enclosure. These controllers included an internal fan for air circulation. 

The AC Servo 1391 controllers convert a 3-phase input voltage at 50 to 60 Hertz to variable voltage with controlled amplitude, phase, and frequency values. The output is used to regulate the speed and/or torque of a 1326 AC servo motor. The AC Servo 1391 controllers are available in ratings of 15 Amps, 22.5 Amps, and 45 Amps RMS with all these current ratings available in the same package size. The corresponding output power ratings are 5 kilowatts, 7.5 kilowatts, and 15 kilowatts, respectively. The rated ambient temperature for the AC Servo 1391 controllers is from 0 to 60 degrees Celsius and the storage temperature is from 0 to 65 degrees Celsius. The output of the integrated cooling fan is 50 CFM. The AC Servo 1391 controllers must be mounted inside suitable enclosures where they are protected from contaminants such as oil, dust, and coolants.