Universal motor
![Modern low-cost universal motor, from a vacuum cleaner. Field windings are copper colored, toward the back, on both sides. The rotor's laminated core is gray metallic, with darker slots for winding the coils. The commutator (partly hidden toward the front) has become dark from use. The large brown molded-plastic piece in the foreground supports the brush guides and brushes (both sides), as well as the front motor bearing.](/Images/godic/202502/18/Universalmotor_35839.JPG")
![Universal motors' field coils are series wound with the rotor coils and commutator](/Images/godic/202502/18/Universeelmotor.svg5839.png")
![Equivalent circuit](/Images/godic/202502/18/ESB_Einphasen-Reihenschlussmotor.svg5839.png")
The universal motor is so named because it is a type of electric motor that can operate on both AC and DC power. It is a commutated series-wound motor where the stator's field coils are connected in series with the rotor windings through a commutator. It is often referred to as an AC series motor. The universal motor is very similar to a DC series motor in construction, but is modified slightly to allow the motor to operate properly on AC power. This type of electric motor can operate well on AC because the current in both the field coils and the armature (and the resultant magnetic fields) will alternate (reverse polarity) synchronously with the supply. Hence the resulting mechanical force will occur in a consistent direction of rotation, independent of the direction of applied voltage, but determined by the commutator and polarity of the field coils.