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How to change the direction of a DC motor?

Suppose you’ve installed your DC motor. But upon starting the engine, you realize that the motor is rotating in the wrong direction. What a mess!

The first question that arises in your mind is, “Can I change the rotation direction of a DC motor?”

Yes, DC motor can run in both clockwise and counter-clockwise directions, easily changing the direction by inverting the polarity of the applied voltage.

Revise Polarity Of Motor

In this article, I will share some practices to change the direction of a DC motor by yourself.

Gear up!

Types of DC Motors

 

Let’s understand the different types of DC motors because each type requires different but straightforward methods for changing the direction.

There are two main categories of DC motors.

  1. Brushed DC motor
  2. Brushless DC motor (BLDC Motor in short)

Brushed Vs Brushless Dc Motor

Brushed DC Motors

 

They are further divided into:

  1. Permanent Magnet DC motor or Low Voltage DC motors
  2. Electromagnetic DC motor or High voltage DC motors

At Prorich, we focus on manufacturing low voltage brushed DC motors. So we will mainly discuss permanent magnet DC motors.

Permanent Magnet DC Motor 

 

Permanent magnet DC motors use 24V or below to create a permanent magnetic field. This type of motor caters to small applications such as Educational Toys, Model Trains, Micro Drones, Toothbrushes, etc.

In PMDC motors, you can change the direction of the shaft by reversing the polarity only. Another method is to use an H-bridge.

Brushed Dc Motor

Electromagnet DC motors

 

They are as under.

Shunt Wound Motor

 

The shunt-wound motors use field coils connected parallel to the armature windings. The connection provides the same supply voltage to the field wire and armature.

They are commonly called constant flux motors, regulating their own speed regardless of load.

To change the direction of rotation of DC shunt motors, reverse the armature or field current.

Type Of Dc Motors

Series Wound Motors

 

In a series DC motor, the field coils and armature windings are connected in series. The field winding in the series wound motors receive more current than any other type of DC motor. And they have the highest starting torque with the most excellent no-load speed.

The high torque makes these motors an optimal choice as a starter motor. But with light loads, the chances of series-wound motors running at high speed are high. Unlike DC shunt motors, series wound motors cannot regulate their own speed.

If we reverse the polarity of the supply to the coils, there will be no effect on the rotation direction of the motor. It is because the current in the armature windings and field winding is already reversed.

Compound Wound Motors

 

A compound wound motor is a mixture of shunt and series wound DC motors. It has two field coils where one coil is connected in series with the armature winding. While the other connected in parallel.

It’s a combination of shunt and series-wound motors. Hence, it shows the best features of both. For example, a high starting torque and exceptional speed regulation.

Can a DC motor be Reversed?

 

Reverse Motor Polarity

Yes. The best part about an electric motor is the ability to run in both directions. So, it can be structured to turn in either direction.

The question remains, “How to change the direction of a DC motor ?”

By inverting the polarity of the applied armature voltage by reversing the polarity of armature winding.

Good news! This method works with all types of DC motors: shunt wound, series wound, and compound wound. 

Why Change the Direction of DC Motor?

 

Now that we know that changing the direction of a motor is possible. Let’s discuss some real-life examples where the change in direction rotation of a DC motor is necessary.

The ventilator moves forward by pushing in and out of the enclosed place. Thus, the change in direction of the DC motor is necessary.

Also, when we install a pump, the conveyor belt should correspond with the speed of the motor. Similarly, brakes might fail while driving a fast car. To produce torque in an opposite direction, reverse the polarity of the supply voltage and your car will stop. 

Thus, changing the rotation direction of the DC motor has a direct impact on overall machine performance and outcome.

How to Change the Direction of a DC Motor?

 

First of all, let’s determine the rotational force of a DC motor i.e., torque. The torque of a DC motor depends on the following factors.

  • 1. Magnetic Flux
  • 2. Armature current

If we reverse the direction or change the field’s polarity through the armature wires, the direction of the motor will reverse.

But, make sure to reverse one factor at a time, either the armature or field wires. Otherwise, the motor will continue to rotate in the same direction. Usually, reversing the field excitation voltage reverses the DC motor direction.

Usually, you will find DC motors that are set up in a fixed direction of rotation to perform particular jobs. 

But, sometimes, the need to change the direction of rotation arises, such as motors for gun or missile launchers. Such motors should move in both directions.

All in all, the direction of your DC motor can be reversed in two ways;

  • 1. By changing the polarity of the supply circuit or field wires
  • 2. By changing the polarity in the armature supply

How to Reverse the Direction of a DC Series Motor?

 

The above method only applies to a separately excited DC motor. But in the case of the DC series motor, things are different.

The field windings and armature winding are connected in series in the series combination DC motor. And so, the field current and armature current are always equal. Now, if we change the polarity of the applied armature current, the direction of the field voltage and armature voltage both change, and the speed will remain unaffected.

Hence, for DC series motors, the change in polarity of armature voltage has no impact on the speed.

The direction of DC series motors can be changed if the polarity of either the field or only armature is altered.

How to Control the Rotation Direction of DC Motor?

 

You can handle DC motor direction by controlling the machine or through any automatic motor controlling tool.

There are three ways you can control the direction of your DC motor.

Manually Reverse the Armature Leads

You can reverse the armature leads of your DC motor to change the polarity of the DC motor’s circuit. The process is pretty straightforward. The DC motor’s user guide contains all the information about the circuit drawings of the negative or positive terminals.

This way it’s pretty easy to reverse the armature leads of your DC motor manually.

Installing a Switch into the Circuit

 

This is by far the easiest method. You can install a switch into the circuit that allows full control of the polarity of a DC motor.

Changing the direction of the motor’s output shaft is a matter of a flip of the switch!

Connect an H-Bridge Circuit

 

H Bridge Diagram

The name, H-bridge, stems from the actual shape of the circuit that controls the motion of the motor.

You can install a double pole, double throw switch (DPDT switch), which is four switches in one that makes an H-bridge. An H-bridge helps you to handle your DC motor effectively when the switches are opened or closed in pairs.

The only disadvantage of an H-bridge circuit is the need for a high current to run the motos that result in dissipation. Thus, to cool the circuit, heat sinks are used.

Cautions You Need to Know When Running a DC Motor in Reverse

Did you know? Your DC motor uses carbon brushes with beveled edges to drag over the commutator. 

When you reverse the direction of your DC motor, it pushes the carbon brushes over the commutator. This results in producing more friction in one direction and causes fast wear and tear of the carbon brushes. 

These worn brushes cause serious damage to the non-interchangeable commutator segments.

Thus, I always recommend checking your motor’s datasheet.

Carbon Brush

Conclusion

 

Now you know what to do with your electric motor running in the wrong direction!

Changing the direction of DC motors is as easy as ABC. Just reverse the armature leads while following the above-mentioned practices, and you’ll be good to go!

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