1. AC or DC
2. Determine HP needed
3. Soft starting capabilities
4. Dynamic breaking module
5. Single-phase to three-phase inputs
6. Drive software
7. Weatherproofing enclosures

Choosing the right speed controller will extend your motor's lifetime and maximize efficiency in all operational phases. The right speed controller or Variable Frequency Drive (VFD) reduces wear and tear on the motor, the electrical infrastructure, and driven load while maintaining peak productivity. It is important to choose a controller that can optimize your operation. Brands such as KB Electronics can offer a diverse, affordable, and customizable range of drives and accessories and hassle-free installation.

Here are the 7 important considerations when deciding on a speed controller:

1. AC or DC

The first step when choosing a drive is to make sure it matches the motor's power supply. The speed of an AC motor is determined by the frequency of the AC power supply, whereas DC motors are controlled by varying the DC supply voltage. Brands like KB Electronics can supply you with drive solutions for a range of both AC and DC applications, as well as custom controllers for OEM applications involving brushless DC, PMSM, PSC and shaded-pole motors.

2. Determining the HP Needed

Secondly, check that the drive is designed to handle the power required by your motor under maximum load. This will result in considerable savings in maintenance and replacement costs. KB Electronics offers several line-ups of speed controllers for AC motors up to 30 hp and DC motors up to 5 hp.

3. Soft Starting Capabilities

Inertia plays a vital role in starting and stopping. When it comes to starting a motor, introducing a large surge of electric current and mechanical shock can cause serious damage to the motor and its components. Soft starters can alleviate this problem by gradually increasing the torque of high-powered motors with high inertia driving loads. Another consideration is whether or not your application starts with a heavy load. Heavy loads require sufficient breakaway torque to get your application started. Some drives were designed to create additional torque at startup to handle these situations. Whether you are looking to smoothly start your application by limiting the inrush current or ramping up your torque to get your heavy loads moving, some drives can handle one or the other or both scenarios.

Motor “Slip”

Once the motor starts rotating, an electric motor drive must precisely manage the motor's speed over the full range through variations in the load. While DC motors generally provide consistent torque over the entire speed range, AC motors suffer from loss of torque at lower speeds and a phenomenon known as ‘slip’ where the rotor rotates slower than the supply frequency as the load increases. Without a speed controller capable of compensating for this, it will not be possible to maintain consistent speed with varying load.

4. Dynamic Braking Module

When it is time to stop a motor, braking needs to quickly and smoothly bring the driven load to a halt. Additionally, when power stops being applied to a motor, a heavy load's momentum keeps the motor spinning (a situation known as an ‘overhauling load’). When this happens, the motor begins to act as a generator, leading to potentially damaging voltage spikes in the electrical system. This is where dynamic braking comes in.

Dynamic braking is a method used to solve both problems by dissipating the power produced by an overhauling load as heat, creating an electromechanical braking effect on the motor. KB offers a simple-to-install Dynamic Braking Module (DBM) for selected drives that achieves a considerable 25% dynamic braking torque and 100% instantaneous braking torque to quickly and safely bring the load to a stop.

5. Single-Phase to Three-Phase Inputs

Ensure the electric motor drive can be operated from the power supply you have available. Drives are also used to convert input power supplies to match the needs of the electric motor. AC drives receive the AC power supply's voltage and frequency and convert it to the motor's full frequency range. If your power supply is single-phase and your motor requires a three-phase power supply, a variable frequency drive is used to convert your single-phase to a three-phase power supply for your motor. If this is something you need for your setup, pay attention to your VFD input and output phases. There are single-phase input/3-phase output solutions for AC drives and DC solutions with single-phase AC input.

6. Drive Software

An electric motor drive is often part of a sophisticated and highly automated control system. It is critical to choose a product that cannot just run its own software but also integrate easily with existing and future infrastructure. Interfacing capability is paramount to provide outstanding flexibility. KB Electronics offers various drives with an ‘SI’ interface port, which allows them to plug into many common fieldbuses, seamlessly integrating it into your current system. Many KB options come with an integrated PLC, enabling you to program your own control software. It has a range of I/O connections for building your own custom control system.

An electric motor drive solution customized for your specific application will also provide you with the ability to optimize and troubleshoot your operation with user-friendly tools and network integration. KBConnect is a PC software tool from KB Electronics designed to give the operators access to the information they need to quickly achieve the speed controller's peak performance and maintain it at all times. To achieve next-generation network connectivity, KB also provides controllers that are capable of remote diagnostics with optional industrial Ethernet and fieldbus communication, enabling off-site monitoring and troubleshooting of the application.

7. Weatherproofing Enclosures

In applications where the environment might be challenging, it is necessary to choose a speed controller that can handle the physical environment that it is in. If the VFD is exposed to harsh weather, high humidity or any harsh environment, a totally enclosed housing is needed. KB Electronics offers speed controllers for applications in all kinds of environmental conditions, with enclosures rated IP20, NEMA 1/IP50 and NEMA 4X/IP65.

Having the right accessories means that you can make the most of your speed controller and further customize it for your specific requirements. With a range of extras, including signal isolators, line filters, multi-speed boards, memory modules, switch kits and more, a comprehensive supplier like KB Electronics can provide you with all the parts you need to fine-tune every part of your application.


Choosing the right speed controller requires the following: motor type, operational requirements, power supply, and control system infrastructure and operating environment. It should be customize-able to your application needs. KB Electronics offers a wide range of products that can help you optimize and troubleshoot your applications.