Electric Motor Starter | Their Functions, Types, and Troubleshooting

In industry, commerce, and even at home, appliances and machinery rely on electric motors. Motors help run tools and equipment ranging from small everyday appliances to huge machinery, but each motor also comes with a starter. Gaining knowledge on the function of a motor starter can help avoid downtimes and ensure smooth running of operations.

The Basics

The role of an electric motor starter is to protect the motor from high inrush current after voltage is applied on its terminals, by controlling the switching mechanism to provide power at a specified time. Automating a motor controller starts from two main functions — switching the power on and off at the appropriate time, and selecting the right amount of power to be fed into the motor, with respect to the workload being utilized by the motor.

More simply, a starter acts as an intermediary between the power source and the motor; it governs the starting sequence and safeguards the motor against potential overloads or faults. In broad terms, starting devices have the following components:  

Overload Protection: This prevents excessive overheating of the motor by shutting it down if current consumption exceeds a certain limit.  

Contactor: A switch responsible for turning on and off the power supply to the motor.  

Thermal Overload Relay: A device providing protection against overheating or overload damage to the motor.  

Fuse or Circuit Breaker: Prevention of faults provides protection from overheating of electrical circuits.  

Electric motor starters are integrated in a variety of equipment, ranging from industrial machines to HVAC units, in ensuring that the operation of the motor is not only effective but also safe.  

What is the process of an electric starter motor?  

In addressing the question on how an electric starter motor functions, it is crucial to emphasize that the starter, as its name suggests, must render the initial rotation of the motor as easy and smooth as possible.  

Here’s what it does:  

Power Flow: The starter motor permits the current to pass to the principal motor when the motor is turned on. This is made possible with a contactor or switch that completes the circuit.

Initial Activation: With the aid of the starter, the motor obtains initial current which helps the motor begin to rotate. Rewound motors use different types of control methods to aid in the starting of the motor. Resistor-based controls, capacitor based circuits, variable frequency drives, and other types may be used.

Protection Features: Starting the motor is accompanied with a current surge and the motor may be subject to thermal overload. The starter protection features take care of these due to their monitoring and controlling of current and temperature level. If too much current is passed through the motor causing overheating, the starter will break the circuit to protect the motor.

Smooth Transition: After the motor has reached running speed, the changeover from starting to running must be smooth. The starter cuts off the extra starting current. This must all be done without shock to protect sudden shocks to the motor that could cause damage.

What Are the Two Types of Motor Starters?

The two types of motor starters are direct-on-line or DOL starters and star-deltas starters. Each of these have their advantages and can be used for different applications of the motor.

1. Direct-On-Line (DOL) Starters  

The Direct-On-Line (DOL) starters are the most uncomplicated and widely accepted methods used with electric motors. This is achieved by mechanically connecting the motor to the power supply of the system. Consequently, it enables the application of the full voltage immediately, thus, it is referred to as a DOL starter. These types of starters are most common for small motors (usually 5 horse power).  

How it works:  

When powering the DOL starter on the motor, the entire load is present on the starter which translates to instant operation for the motor.  

The motor circuit is closed using a contactor and a thermal overload relay is used for overheating or excessive current damage protection.  

Advantages:  

Easy to install and maintenance free.  

Affordable solutions.  

Disadvantages:  

It can lead to a plethora of consequences like high motor current, power supply current, and motor torque which can negatively influence motor health and the wider electrical network.  

Large motors are yet another consideration for these types of motors as there is no known precise measurement for speed control.  

2. Star-Delta starters  

These types of starters are advanced in comparison to others with motors operating at 5 horsepower and above. It lowers the starting current due to specific types of wiring that reduces the voltage that is supplied on start.

How it works:

In Star configuration, the motor is connected in a manner that caps the voltage and decreases the starting current. After the motor has achieved a predetermined speed, the starter switches to delta configuration, which is where the motor is fully connected to the voltage.

The change from star to delta happens on its own once the motor reaches about 80 percent of its total speed.

Advantages:

Helps reduce inrush current that can potentially damage the motor and electrical infrastructure.

Appropriate for bigger motors and high power usage scenarios. 

Disadvantages:

Requires more care and complicated setup.

Not appropriate for motors that need the maximum rotational speed instantly upon starting.

How to Diagnose a Break in an Electric Motor Starter

A worn out electric motor starter can come as a result of prolonged usage. Other than that, signs of a malfunction should be a red flag indicating your motor starter needs servicing. Here is a list of signs that indicate an electric motor starter is having problems: 

1. The Motor Is Inoperable

Most electric motors tend to come with basic starters. If your motor does have one attached, but there seems to be no operation after activating the electric motor, the problem could be traced back to the starter not being able to energize the motor. Considering all the above issues, we can arrive with an electric contactor problem, overload relay that blew, or burnt fuse. 

2. A Drastic Change in Operating Temperature

An increase in temperature of the starter or disjointed motor that are part of the construction can mean a problem in the supply to the motor. A high temperature can result as a direct consequence in a present motor load which is too high, faulty electric wiring or a badly malfunctioning starter.

3. Peculiar or Unusual Noises  

An unusual noise like buzzing or humming typically means that the starter’s components are having issues. This could result from a failing contactor or a worn-out relay. It often signifies that there is excessive current or friction flow, which if not managed could lead to motor damage.

4. Blown Fuses or Tripping Circuit Breaker  

Excessive current draw which stare often connected with starter problems is suggested if the circuit breaker frequently trips. This may happen with an overload relay fault or starter built short circuit. An overload relay failure or built circuit within the starter might cause this.

5. Stalling or Irregular Motor Speed  

If the starter fails to deliver proper current to the motor, it may run at inconsistent speeds or stall soon after starting. Inadequate power supply can lead to motor damage and poor performance. Erratic power delivery is damaging to the motor which may cause it to fail.

6. Visual Inspection  

Performing a thorough visual inspection on the motor can sometimes prove to be useful. Look for failed burnt or damaged protective elements and dismantle wiring covered loose binding. These signs are likely to suggest starter failure.

Electric Motor Starter Essentials  

The functioning of electric motors is fully automated and integrated with technology, sophisticated electric motor starters allow for safety and optimal efficiency. Promptly addressing the electric motor’s starter components promotes effortless operation of other motor parts, helping avoid unplanned business halts due to expensive repairs.  

With a Direct-On-Line (DOL) starter, or an electric motor’s star-delta starter, the user can take advantage of each unique benefit in terms of size and application scope of the motors they use. Identifying issues with a motor starter is crucial as it optimizes value for resources and prevents premature damage to the electric motor.  

To put it succinctly, the starter’s role is crucial to ensure problem-free operation and service longevity for people working with electric motors.