When purchasing electric motors, there are a number of options to choose from – it’s not just a case of working out what power you need and choosing the cheapest. There are a number of different kinds of motor available, and the best choice will not only depend on your budget, but also on what type of application you intend to run.
To help you choose the best electric motor for your exact requirements, we’ve developed this handy guide. Here, we’ll explain the different types of electric motors that are available and we’ll give real-life examples of where they are best used. After reading this guide, you should have a better appreciation of the type of motor you need to purchase – then you can start to think about power outputs and budget.
Three-Phase Electric Motors
Three-phase electric motors are the most powerful and efficient commercial motors, and as a result, they are usually found in large commercial applications such as lifting gear, large conveyors and heavy duty compressors. But what exactly is a three-phase electric motor and can they be used on a 240v mains power?
The electricity you get from the grid is supplied as alternating current. As its name suggests, this means the current alternates cyclically, flowing in one direction on the circuit before reversing to flow in the other. In the UK, alternating current is supplied at 50hz, which means the current alternates its flow 50 times a second. While this is happening, the voltage levels vary between positive and negative amplitude. While this is fine for most small electrical appliances like electric drills and microwaves, it can cause problems for larger equipment which requires a constant flow of electricity.
To solve this problem, three-phase motors provide three streams of alternating current set at different phase angles. When the windings are set correctly, this ensures that each stream reaches maximum current approximately ⅓ of the time, effectively creating a constant flow of electricity. Three-phase motors are extremely efficient and reliable for operating large machinery since they draw less current than a single phase motor, however, they are typically more expensive to purchase and may require three-phase power to be installed at your premises.
These motors are suitable for a range of commercial applications in wet or dry environments and can be supplied with either a foot or flange mountings, depending on your application.
Single Phase Motors
If three-phase power is unavailable or impractical to install, you will have to use a single-phase motor. While these may lack the efficiency of three-phase motors, when correctly sized and rated, they can provide many years of trouble-free usage. When choosing a single-phase motor, it’s important to pay careful attention to your application and its power requirements. Choosing a power rating that is too small will result in repeated motor failures, while running a motor at less than full rating is not efficient and will cost you thousands in wasted electricity payments.
This type of motor is most suitable for powering small domestic or commercial applications including fans and blowers, electric gate and warehouse door operations, along with small pumps, conveyors, refrigerators and drills. Single-phase motors are cheaper to purchase and install than three-phase motors, but they cost more to run per hour because they draw more current.
It is important to bear in mind that this type of motor should never be used to hard start large applications. We recommend using a separate start/capacitor to run single-phase motors to help prevent motor failure.
Braked Electric Motors
While getting your motor to spin is easy, slowing it down is a different matter. Without brakes, the only way to stop your motor spinning is to let it coast to a standstill. While this doesn’t take long on a small single-phase motor, it can take a significant amount of time on a larger three-phase one. Allowing a motor to coast is also not suitable for many stop-start applications such as conveyors, drills and lathes.
For such applications, we recommend braked motors. As the name suggests, braked motors contain a brake which can slow down or stop the rotors when required. A range of breaking methods can be used to slow and stop the rotors, but for most applications, we recommend D.C. injection braking combined with regenerative braking to dissipate heat.
This braking method introduces a pulsating D.C. current into the motor windings to create a stationary magnetic field to slow the rotors, while dynamic energy from the spinning rotor is converted into electrical energy and fed back into the injection system. This type of braking mechanism is the most efficient braking method for three-phase motors and provides a reliable stop-start mechanism which is both reliable and energy efficient.
Contributed by Krysta Jackson:
