The universal motor is a special type of motor that is created to operate with almost the same features as AC as well as DC power. Commutator machines are used in universal motors.
- Universal motors powered by single-phase alternating current work at speeds ranging from 3000 to 2500 rpm and have a power rating of up to 1200 watts.
- Their speed rotation is only limited by the mechanical strength of the rotor and bearings as well as the usable brush lifespan.
- Universal motors are used in portable tools and different types of equipment.
- The structure of the universal motor is similar to the exactly to the DC motor.
Characteristic of universal motor
- The universal motor is much less expensive.
- The universal motor has a high changeable speed.
- A universal motor's speed is low at full load and very high at no load. The motor is operational.
- This motor has a high changeable speed.
- It is a single-phase series motor.
- These motors are very portable.
- The motor generates a lot of transmitting torque.
- This motor is a type of commutation motor.
- Universal motor work with high efficiency in DC supply.
- The universal motor produces a unique wiring sound when operational.
- It runs at a lower speed when using an AC supply due to a voltage drop in reactance.
- A universal motor at full load about 90% of the power factor
This unique characteristic of the universal motor of being able to operate at all types of voltage makes it universal.
Speed/load characteristics of universal motor
Speed/load characteristics of the universal moor are similar to that DC series motor. The speed of a universal motor is low at full load and the highest at no load. Gear trains are made use of to get the required speed at the required load. The speed/load characteristics for both AC as well as DC supply are shown in the figure below.
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| Speed/load Characteristics |
Construction of universal motor
The construction of a universal motor is very similar to the construction of a DC machine. A stator is mounted on which field poles are attached. Field coils are would on the field poles. Still, the whole magnetic ath is laminated. when operating on AC, lamination is required to minimize eddy current.
Stator
A stator is a part that does not move. It is a stationary part, which contains the following components
- Field coils
- Laminated case
- Wiring from source
- Brushes
Rotor
The rotor is a rotating part, it consists of the following main part
- Shaft
- Commutator
- Rotor windings
Commutator
Commuters work like a reverse the direction of current in the rotor and external circuit. So we make sure that the current flowing through the rotor winding is always in the same direction.
Brushes
These are the components of the stator that help in the passage of current to the rotor, or moving section, of the universal motor. Brushes are often produced from graphite.
Frame
the frame is built of steel or rolled iron shells. It is in charge of keeping the magnetic field and motor body laminations in good condition.
Working of universal motor
A universal motor can be powered by a direct current (DC) or a single-phase alternating current(AC) source. When a DC supply is connected to the universal motor, it operates as a DC series motor. An electromagnetic field is created when electricity travels through the field winding. The same current runs through the armature conductor as well. When a current-carrying conductor is placed in an electromagnetic field, it experiences a mechanical force. As a result of this mechanical force, or torque, the rotor begins to rotate. The direction of this force is determined by the burning left-hand rule.
When creates unidirectional torque powered by an alternating current supply. Because the armature and field windings are linked in series, they are in the same phase. As a result as the polarity of AC changes regularly, the reaction of current in the armature and field winding reverses at the same time.
As a result the direction of the magnetic field and the direction of armature current reverse, while the direction of force experienced by armature conductors stays constant. Thus, regardless of whether the power source in AC or DC universal motors operates on the same principles as DC series motors.
Application of universal motor
- Universal motors are found in portable drills, blenders, and other similar devices.
- They are commonly seen in portable drill machines.
- Polishers, blowers, food mixers, vacuum cleaners, and kitchen equipment all use them.
- Table fans, hairdryers, and grinders all employ universal motors.
Advantages of Universal motor
- The cost of the motor is higher than ordinary brushed and quite less than brushless.
- The main advantage of a universal motor is it is lightweight.
- It is simple design and cheap.
- It is very high speed.
- It is easy to construct and inexpensive.
- It is smaller in size allows it to be used in the smallest device.
- In universal motors, the main parts are quite durable.
- They are capable of generating a high number of revolutions.
- The universal motor is ideal for small appliances that require high power.
- The cost of a universal motor is a little higher than an ordinary brushed one and quite less than a brushless one.
Disadvantages of Universal motor
- Speed control is lousy.
- It is not easy to reverse the motor.
- The efficiency range of 55-80% and it depends on source type.
- The universal motor has a high maintenance cost and short life commutator.
- When working with voltages up to 100 V.s, the efficiency drops dramatically.
- Universal motors produce more noise and vibration than induction motors.
- This motor is in direct contact with the brushes with the collector, they require periodic replacement or repair.
Summary
In this article, you will understand the details of the universal motor and its characteristics, construction, working principles, Speed, load characteristics, advantages, disadvantages, and applications. So we all understand that universal motors run at very high speeds at no load, which is quite dangerous. Also this article we also discuss that this type of motor is unique its power is dependent on both AC and DC.
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