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How Does a Universal AC Motor Work?

A universal motor can be defined as a special kind of motor that is designed to operate on either single phase AC supply or DC. Their name is derived from the fact that they are able to run on both AC and DC. Universal motors are available in 2 types i.e. uncompensated type and compensated type. Universal motors have variable speed characteristics and a high starting torque. This is the main reason why universal motors arrive built-into devices that they are designed to drive. Most universal motors can work at very high speeds i.e. 3500 RPM. How does a universal AC motor work?

How does a universal AC motor work?

When a universal motor is fed with an AC supply, it produces a unidirectional torque. Field winding and armature winding are in the same phase because they are connected in series. The current direction in field and amateur winding reverse simultaneously because the polarity of AC alters periodically. This makes the direction of armature current and magnetic field to reverse such that the direction of the force experienced by the armature conductors is constant. In AC supply, polarity is altered between -ve and +ve and this happens about fifty times in every second. This is what changes direction of the magnetic field and current hence the resultant force in varying direction.

How does a universal AC motor work? It works on a similar principle to the DC series motor. This means that the nature of the supply i.e. AC or DC makes little difference. However, it should be noted that universal motors that run on AC supply do so at a lower speed compared to DC supply and this is for a similar voltage. This is attributed to a reactance voltage drop that is experienced in AC alone.


After comprehensively addressing the query i.e. how does a universal AC motor work? It is good to look at some of its applications:

i. Universal motors are heavily used in numerous home applications such as domestic sewing machine, drink and food mixers, vacuum cleaners etc.

ii. Universal motors of a higher rating are found in blenders, portable drills etc.

Next time that you use any of the above applications, you can comfortably answer how does a universal AC motor work?


A universal motor’s electrical design include armature windings, field windings, cooling system, insulation, commutator and brushes and magnetic circuit. How does a universal AC motor work? Now you know. 

Keywords in the article: Auto Motor,Brushless Motor,Universal Motor,PMDC Motor,Gearbox Motor