Types of DC Motor

We know that there are two types of motors, namely AC and DC. The AC motor uses AC current to transform electrical energy into mechanical energy. There are many types of AC motor. The DC motor uses DC current to transform electrical energy into mechanical energy. The main advantage of using this is that we can control the speed, and it occupies less space.

There are 4 major types of DC motor. They are:

• Series DC Motor
• Shunt/Parallel DC Motor
• Compound DC Motors
• Permanent Magnet DC Motor

In the case of a permanent magnet DC motor, permanent magnets are used to create field flux. The other three types are classified based on the electrical connections between the stator and the rotor. Each of them has a unique torque/speed.

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Classification of DC Motor

Based on the type of construction and electrical connection, DC motors can be categorised into four major types. A brief chart (based on the type of construction and electrical connection) is given below:

Types of DC motor when listed sequentially:

• Permanent Magnet DC Motor
• Shunt Motor
• Series Motor
• Compound Motor is again classified into
• Short Shunt Motor
• Long Shunt Motor
• Differentially Compound
• Cumulative Compound

Permanent Magnet DC Motor

In these types of DC motor, the permanent magnet is used to create a magnetic field. In this, no input current is consumed for excitation. These are used in automobile starters, wipers, air conditioners, etc

Shunt DC Motor

Here, the field is connected with the armature windings in parallel or also known as a shunt. The shunt field can be separately excited from the armature windings and that is the reason it can be used for greater speed regulation and can also offer very simplified reverse control.

Series DC Motor

Here, a large wire carrying the full armature current winds the field with few turns. This kind of motor generates a large amount of starting torque but the speed cannot be regulated here. If they are run with no load then it might face damage. These are not the ideal option for variable speed applications.

Compound DC Motor

These have a shunt field which is separately excited. They have a good starting torque but might face problems in variable speed applications.

Short Shunt DC Motor

Here, the shunt field winding is only connected with the armature winding and that too in parallel. The field coil, which is in series, is entirely exposed to current before being split up into the armature.

Long Shunt DC Motor

Here, the shunt field winding is connected in parallel with the both series field coil and armature which are again connected with each other in series.

Differentially Compound DC Motor

In this type of compound wound DC motor, the flux produced due to the shunt field windings reduces the effect of the main series windings.

Cumulative Compound DC Motor

Here, the flux produced by the shunt field windings enhances the effect of the main field flux which is produced by series winding.

Frequently Asked Questions

Q1

What is the function of permanent magnets in a permanent magnet DC motor?

A permanent magnet DC motor uses permanent magnets to create field flux.

Q2

What is a series motor?

A large wire carrying the full armature current winds the field with few turns. This kind of motor generates a large amount of starting torque but the speed cannot be regulated here.

Q3

What is a compound motor?

These have a shunt field which is separately excited. They have a good starting torque but might face problems in variable speed applications.

Q4

What are the types of compound excited DC motors?

The types of compound excited DC motors are short shunt motor, long shunt motor, differential compound, cumulative compound.

Q5

What are the types of self-excited DC motors?

The types of self-excited DC motors are shunt excited, compound excited and series excited DC motors.

Q6

What happens when the speed of a DC motor increases?

When the speed of a DC motor increases, back emf increases but there will be a fall in the line currents. This is because speed is proportional to the back emf. If there is a series motor, the armature current will be equal to the load current.

Q7

How to determine the direction of rotation of the motor?

The direction of rotation of the motor is determined by Fleming’s left-hand rule. The law states that when the current-carrying conductor is placed in the magnetic field, there is a force acting on the conductor, and on the other side of the conductor is forcefully kept under a magnetic field, there will be an induced current in the conductor.

Faraday’s Law of Electromagnetic Induction Explained

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Type Of Motors

Shaded Pole Motor 

Shaded pole motors are the original type of AC single-phase induction motor. Also called a single phase induction motor, simply connecting to a single voltage line and an external capacitor is required to make this motor turn. The different types of single phase induction motors vary depending on the method used to started them. The four basic types are split phase, capacitor start, permanent split capacitor, and capacitor start/capacitor run.

Split Phase Motor

A split phase motor uses a switching device to disconnect the start winding once the motor gets to 75% of its rated speed. Although this type has a simple design which makes it less expensive for commercial use, it also has low starting torques and high starting currents.

Capacitor Start Motor

The capacitor start motor is a split phase capacitor motor with a capacitor in series with the starting winding to create more starting torque. This motor is more expensive due to the switching and capacitor components that are required.

Permanent Split Capacitor

A permanent split capacitor motor does not have any starting switch. For this type, a capacitor is permanently connected to the starter winding. Since this requires a capacitor for continuous use, it does not provide starting power, therefore starting torques are typically small. These motors will not perform well for heavy starting load applications. However, they do have low starting currents, quieter operation, and higher life/reliability, thereby making them a good choice for high cycle rates. They are also the most reliable capacitor motor on account of not having a starting switch. Different designs offer higher efficiencies and power factor at rated loads.

Capacitor Start/Capacitor Run Motor

The capacitor start/capacitor run motor has both a start and runs capacitor in the circuit. Once achieving full start-up, the start capacitor is disengaged.  This type of motor has higher starting, lower loaded currents, and higher efficiency. The drawback is the expense required for two capacitors and a switching device. Reliability also plays a factor on account of the switching mechanism.

The Technology

To compare, this resistance split induction motor types supply only a low to medium amount of starting torque, and this restricts them to the low power applications they are best suited for. These motors use a single auxiliary winding smaller than typical, creating a lower inducting rate and much higher resistance than other types.  Simple models like these can only be used when the load is low, and there is little starting drive needed.

Some applications, like small fans, grinders, and heaters, do not need the higher starting torques but in most cases, the more torque at starting the motor, the more of a load can be put on the machine. A Single phase motor that comes with high starting torques often is more expensive than the simpler split induction types. However, the difference in power can be worth it for different industrial needs. In a single phase motor that has a high starting torque you can expect a different level of performance, this can save time and energy.

The alternating currents that flow in a single phase motor reach their peak values at the same time; this makes one single phase. In a three phase systems,  peak current values are achieved in a sequential fashion, making three separate stages. To compare to three phase systems, these motors do not have the same high-efficiency levels but can last indefinitely with little maintenance.

Induction electrical motors have different classifications according to the source of electric power and type of construction. Induction type motors, also called asynchronous motors, operate using an alternating current (AC) produced by electromagnetic induction, as opposed to the commutators commonly used in other AC motor types. Induction motors have been used across the industry as well as in standard appliances such as refrigerators, washing machines, dishwashers and clothes dryers.

Induction type electric motors were the original AC motor to be created; Nikola Tesla came up with the prototype in 1883. These induction motors use a very simple design and operation when compared to modern AC motor designs but, they are still very rugged, quiet and durable. Induction motors are distinctive because they use an induced current in the rotor to produce rotational motion.

Induction motors consist of two simple parts, the copper winding stator, and the armature or rotor assembly. The stator windings are held in slots around the stator, with a balance between the number of north and south poles. The rotor assembly comes manufactured in a few variations: squirrel cage rotors, slip ring rotors, and solid core rotors.

These motors are best for low power needs and applications where it would be inefficient to use more high-powered mechanisms. Many single-phase motors are ideal for applications with low inertia while others are engineered to meet high starting torque requirements.