Universal Motor

What Is a Universal Motor?

A unique kind of motor known as a Universal Motor can be powered by both AC and DC power sources. Universal motors are wound in series (the Armature and field Windings are in series). The Universal motors are Typically Integrated into the device they are intended to drive because the series connection enables them to Generate high torque.

The Majority of Universal motors are designed to function at up to 3500 RPM. When powered by DC rather than AC at the same voltage, these motors operate more quickly. This is brought on by the Reactance voltage drop, which only occurs in AC and not DC.

How does a Universal Motor run on both AC and DC supply?

A Series-wound DC motor’s construction is similar to that of a Universal motor. A Universal motors has some Modifications that enable it to function with either an AC or DC power source.

Construction of a Universal Motors (diagram)

The field poles are mounted on a stator, which is the component of a universal motor. The field poles are encircled by field coils. A universal motor’s armature and stator field circuit are both laminated. To lessen the eddy currents generated when using AC power, laminations are required.

The commutator and brushes are supported by straight or crooked slots on the rotary armature of the universal motor. Due to the current induced in the armature coils, the commutation on AC is worse than that on DC. The brushes used have a high resistance because of this.

Operation of Universal Motors

When fed with a DC supply

The universal motor functions as a DC series motor when it is supplied with a DC supply. An electromagnetic field is created in this instance by the current flowing through the field winding. The conductors of the armature carry the same current. A Current-carrying Conductor Encounters a Mechanical force when it is exposed to a magnetic field. The rotation of the rotor is caused by this mechanical force. We can determine the force’s direction using Fleming’s Left-Hand Rule.

When fed with an AC supply

When the universal motor is powered by AC current, a unidirectional torque is created. This is due to the series connection and phase alignment between the field and armature windings. As a result, the direction of the current in the armature and the field winding change at the same time whenever the polarity of the AC changes. The armature current and magnetic field directions are reversed, keeping the armature conductors’ sense of force in the same direction. Therefore, universal motors operate on the same principle as DC series motors, whether they are powered by an AC or DC supply.

Properties of Universal Motors

Following are the distinctive properties of the universal motors:

• They have high starting torque.
• Universal Motors run at high speed.
• Universal Motors are noisy because of the commutator and brushes.
• Compact size and are lightweight.

Characteristics of Universal Motors

Efficiency of Universal Motors

The efficiency of smaller universal motor is around 30%, while the larger universal motor have an efficiency of 70-75%.

Speed Load Characteristics of Universal Motor

The universal motor’s speed is highest when there is no load and lowest when it is fully loaded. To achieve the required speed at the required load, gear trains are used. The figure above displays the speed-load characteristics of universal motors for both AC and DC.

Universal Motor Speed Control

The speed of the universal motor is managed to prevent it from operating at an unsafe speed when there is no load. Including a universal motor in a device that is designed to never operate in no-load conditions is one way to control the speed. Small applications that favour connecting the motor directly to the system it drives favour these setup types.

A few other ways to set the speed of the motor to the desired value is as follows:

• Using a gear train to reduce the actual load speed
• Centrifugal Mechanism
• Resistance method of speed control
• Field Tapping method of speed control

Application of Universal Motor (Universal Motor Application)

When high speed and precise speed control are required, universal motors are used. The following are some of the uses for a universal motors:

• They are used in portable drill machines.
• Universal Motors are used in table fans, hairdryers and grinders.
• They are used in polishers, blowers and kitchen appliances.

Frequently Asked Questions –

What is a Universal Motor, and why is it called so?

A unique kind of motor called a universal motor can function on either a single-phase AC supply or a DC supply. It is referred to as a universal motors because it can operate on both AC and DC.

Where is a Universal Motors used?

Due to their high starting torque and compactness, universal motors are used in portable power tools and equipment.

List two differences between Universal Motors and DC series Motors.

• The universal motors has different winding ratios and thinner iron laminations.
• A universal motors can also operate on AC power, while a DC series motor operates only on DC power.

Can a Universal Motors be used as a generator?

Yes, but a universal motor is a DC series motor, not the kind of generator that works well for a variety of purposes.

How does a Universal Motors work?

When powered by a DC supply, a universal motors functions as a DC series motors. As the current moves through the field winding, a magnetic field is created. The conductors of the armature carry the same current as well. We are aware that an electromagnetic field exerts a mechanical force on current-carrying conductors when they are exposed to the field. The rotor begins to rotate as a result of this mechanical force.