Understand Motor Efficiency and Know When to Upgrade

When is the best time to invest in a new motor for your essential equipment?

The answer might be that you should upgrade as soon as possible.

There are several factors that can impact this decision but understanding motor efficiency will greatly assist in answering this question. These factors are discussed in more detail below.

Motor Efficiency

A motor is used to convert electrical energy into mechanical work, typically through a spinning shaft. During the conversion process some of this energy is lost (commonly as heat and noise).

The efficiency of a motor relates to the ratio of the usable mechanical power and the electrical power supply. A higher motor efficiency means less energy losses, and more usable mechanical energy.

International Efficiency (IE) Classifications for Motors

IE classifications are divided into four groups that are defined by international standards. These groups define the minimum efficiency required for each classification and vary by the size of the motor.

These classifications groups are: IE1- Standard Efficiency, IE2 – High Efficiency, IE3 – Premium Efficiency, and IE4 – Super Premium Efficiency. The IE ratings are available online, and generally, a larger difference in efficiency between the groups can be seen for smaller motors.

An example of efficiencies for different motor sizes are shown below:

Rated Power (kW) Poles IE1 IE2 IE3 IE4
0.55 2 69.00% 74.10% 77.80% 81.50%
5.5 2 84.70% 87.00% 89.20% 90.90%
55 2 92.10% 93.20% 94.30% 95.30%

Capital Costs vs. Operational Costs

A more efficient motor will cost more to purchase than a less efficient one. However, over the life of the product, a more efficient motor will usually pay for itself in lower energy costs. This is demonstrated with the following example:

Let’s look at a moderately sized motor that delivers 30 kW of mechanical power to a pump for 12 hours of irrigation each day. If the existing motor is an IE1 rated motor and it is replaced with an IE3 rated motor, the motor efficiency goes from 90.70% to 93.60%. This increase equates to 3,591 kWh of energy saved, or $1,005/year*. If the motor replacement costs around $4,000 to purchase, the new motor is paid back in just 3.98 years!

(*assuming a constant pump load factor and a standard tariff rate)

Maintenance Costs and End of Life Considerations

As well as the operational costs, another benefit of a higher efficiency motor is that they can have lower maintenance requirements and longer life. This depends on the individual motor, though in general, a less efficient motor will result in more energy losses. One of the typical energy losses is heat and excess heat can lead to wear and tear on motor components (such as couplings, bearings, seals, shaft, electrical components). This will result in more costs required for the maintenance and replacement of parts. It also will reduce the overall expected life of the motor.

In some cases, a product’s warranty may give an indication of its expected lifespan; a longer warranty period implies that the manufacturing company has more confidence in the longevity of their products.

Overall, motor efficiency will have the biggest impact on larger motors that have high and frequent usage. The typical operation of the motor should be considered when assessing a motor. It is also important to consider the entire life of a product when making the decision to purchase a motor; whether it is a brand new installation, you are replacing a motor, or retrofitting an existing system.