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The Definitive Guide to Reduce DC Motor Noise

Is your DC motor making funny sounds recently? Or does it feel like a vibrating guitar string? If so, you’re not alone. 

DC motors and noise go hand in hand. But what if I tell you the motor noise and vibration result from some technical problems?

In this article, I will walk you through the main causes of DC motor noise and techniques to reduce them. 

Let’s get started!

Types of Motor Noise

Before jumping into the technicalities, let’s first focus on the two main types of DC motor noise.

  • Electrical Noise
  • Mechanical Noise

Causes of Electrical Noise in DC Motor

The causes of electrical noise in DC motor are as under:

Sparks Occurrence

 

Motor Spark Prorich Motor

One of the main causes of electric noise is the occurrence of sparks. How do sparks occur in your motor? Do you know what happens when your motor is up and running?

The commutator switches the electricity direction that flows through the windings.

An occasional spark occurs between the brushes and the commutators during commutation timings. This spark is one of the main causes of electrical noise.

High Stall Current

 

High Stall Current Prorich Motor

The higher current that flows through the windings causes the motor to make higher noise. Other sources of noise in DC motors are:

The Instability of Motor Brushes

 

When motor brushes lie in an unstable position, such as, on the surface of the commutator.

Higher DC Input

 

High Dc Input Prorich Motor

Higher DC input may cause insulation on the surface of the commutator, which is not normal and leads to electrical noise.

Types of Electrical Noise

Understanding the types of electrical noise helps a lot in troubleshooting the problem.

There are two types of electrical noise:

  • Line Noise: mostly travels through the power cables and in connection cables.

  • Radiation Noise: radiates from the source to the air and leads to interference in radio and TV.

Mechanical Noise

In DC motors, the primary sources of mechanical noise are from:

  1. Bent shaft
  2. Damaged bearings
  3. Poor lubrication of bearings
  4. Missing parts such as screws or other minor pieces
  5. Loose stator core

Furthermore, airborne noise occurs when motor parts are excited at their natural frequency. 

Causes of Mechanical Noise

Let’s now discuss the causes of mechanical noise in detail.

Loose Stator Core

Loose stator core noise is a buzzing sound that is particularly magnetic. Thus, upon removing the power, the noise will stop.

Methods to reduce the loose stator core noise are as follows.

  • Tap the outside of the motor frame with a mallet when the motor is running

  • The noise level will change or may even stop if the tapping deforms the frame-to-core-fit

Bearings

 

Ball Bearing Prorich Motor

Loose or damaged bearings are one of the most common causes of mechanical noise in DC motors. Also, DC motors are very noisy due to the poor lubrication of bearings. But, the sources of bearing noises are distinct and easy to identify, such as:

  • Bearing brinelling gives a low-pitched noise.

  • Dirt in your bearings can increase friction, heat and produce a shrill noise.

  • The insufficient lubrication of ball or roller skidding causes a high-frequency noise.

Brush and Commutator Friction

The friction between the DC motor’s moving parts. For example, brush and commutator, shaft and bearing, all these friction cause noises.

Unbalanced Rotor

 

Unbalanced Rotor Prorich Motor

The unbalanced rotor behavior creates heavy vibrations, leading to thrust noise. Misaligned motor balancing shafts created unwanted, annoying vibrations, resulting in mechanical noise. Let’s say, the radial runout creates noise when shaft and bearing bore clearance is large.

Resonance

Motor resonance causes heavy vibrations that lead to mechanical noise

How Does Motor Noise Impact Your Machine Performance?

Motor noise worsens your machine’s average performance, leading to its downtime. So, you should never ignore both the mechanical and electrical noises. Prompt diagnosis also increases the longevity of your machine.

Pro Tip: Diagnose any noise from your machine immediately to avoid further damage. Otherwise, even a minor issue worsens and leads to irreversible motor damage.

Dealing with DC Motor Noise

As discussed above, many noises are one of the major drawbacks of working with DC motors. It can both affect your motor performance and distort your sensors. In this section, I’ll discuss some helpful tips to reduce DC motor noise.

1. Solder One to Three 104 Ceramic Capacitors Across Your Motor Terminals

 

104 Ceramic Capacitors Prorich Motor

The most popular method to reduce DC motor noise is by installing capacitors. Thus, it is recommendable to solder at least one capacitor over your motor terminals. (as close as possible)

Please note if the noise is too much, solder your motor with two capacitors. 

Furthermore, for greater noise suppression, I tell soldering your motor with three capacitors.

Motor With Capacitor Soldered Prorich Motor

2. Make Your Motor Lead Wires As Short As Possible

When it comes to motor lead wires, less is more.

Short motor wires reduce the noise by twisting motor leads that swirl around each other.

3. Adding a Disk Varistor or Capacitor Inside of the Motor

 

Unbalanced Rotor Prorich Motor

As I mentioned earlier, the major cause of electrical noise is the occurrence of sparks in the motor. 

To cater to this, I insist on installing a disk varistor and attaching it to the commutator. 

In this way, it absorbs the surge voltage that reduces the noise from the DC motor and prevents sparks.

4. Lubrication of Bearing Ends After Motor Assembly

Poor lubrication of bearings causes your motor to make funny noises.

I suggest using adequate grease volume (no more, no less) to lubricate the bearings.

5. Balancing The Motor Rotor

An unbalanced motor rotor creates a centrifugal force on the motor. These centrifugal forces lead to vibrations that produce greater noise.

6. Motor Shaft and Bearing Should be Concentric When Doing Motor Assembly

Bearing failure and misalignment of shafts causes heavy vibrations. And it makes the motor too noisy. 

Concentric locking of bearings will prevent heavy vibrations and disturbing motor noises.

7. Place Your Motors in a Total Enclosed, Shielded Enclosure

A shielded enclosure provides reasonable ventilation that controls heavy noise voltage and vibrations.

Final Takeaway

DC motors are still used because they offer exceptional speed and torque control.

Yet, you should never overlook the noise problems that surround DC motors.

In this article, I’ve highlighted the most common causes of noise in DC motors, and some tips to reduce them.

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