Motor Week: Is an AC or DC Drive Right for You?

The debate between direct current and alternating current isn’t confined to the pages of history, and between the renowned thinkers, Edison and Tesla. The debate is still prevalent on the plant floor when the choice whether to utilize an alternating-current (AC) drive or a direct-current (DC) drive arises. In an effort to more clearly highlight the differences between the two, here is a breakdown of some of the advantages and disadvantages of AC and DC drives.

Alternating-Current (AC)

There are a few significant benefits to the use of AC drives. First, AC drives require very little maintenance and upkeep. One reason for this, is that AC drives do not have brushes, so there are never issues with motor brush wear and the inconvenience and cost of replacements, as well as the resulting downtime. They are also typically a more cost effective motor option, due to their size and more simplistic design.

The speed of operations is important to consider when choosing a motor. The AC drives are particularly effective when working with higher speeds, such as 2500 rpm or higher. The AC drive also provides more controlled acceleration, as well as allowing for adjustable operation speeds and adjustable torque.

The AC drive is not without disadvantages, however.  Two notable disadvantages are speed control and control complexity. An AC drive is not always able to operate at speeds less than one third of the base speed. Therefore, the speed necessary for a motor is an extremely important factor to consider when deciding between an AC drive and a DC drive.

Direct-Current (DC)

Some of the most notable advantages to using a DC drive is high starting torque, control over a wide range of speeds, quick starting, stopping, acceleration, and reversing, as well as accurate step-less speed with constant torque.

Also according to Joliet Technologies, “DC regenerative drives are available for applications requiring continuous regeneration for overhauling loads. AC drives with this capability would be more complex and expensive.”

When choosing a DC drive there are also some important potential pitfalls to consider. DC drives are often high maintenance, requiring care for various parts such as the mechanical interface, the commutator and the brushes. They are also particularly vulnerable to dust, as well as physically more cumbersome – thus, making the location of the motor a very important factor to consider.  Location is also extremely important in regards to DC drives because some areas could prove quite dangerous. For example, DC drives cannot operate in explosive hazardous conditions because of the risk of sparking around the brush.

Industrial motors are crucial for many manufacturing enterprises, so selecting the right drive for unique and specific applications is extremely important.  The two common options are AC drives and DC drives, however, it is important to distinguish between them. AC drives and DC drives are very different and better suited to different applications.