Control Techniques has unveiled its first all-new DC drive for 15 years. The Mentor MP is the result of 20 man-years of development, guided by customer research which revealed that there is still a substantial demand for DC drives, especially if they support modern communications.

"There are a lot of expensive DC motors already installed,” points out CT executive vice-president, Phil Sewell. Users want to keep them, he adds, “but most DC drives lack modern controls, system integration and connectivity. Mentor MP brings DC drives into the modern world.”

CT’s new drive shares the same control platform as its Unidrive SP AC range and includes three slots that accept SP option modules. There is a choice of 18 modules including I/O expansion, a programmable controller, feedback options, and support for Profibus-DP, Interbus, DeviceNet, CANopen, EtherCat, Ethernet/IP and Modbus TCP/IP communications. More modules are planned. The photograph (above) shows a Mentor MP with its front cover removed to show three option modules in their slots.

The power side of the DC drives has also been redesigned with a patent-pending form of galvanic isolation separating the power and control sections. Although such separation is common in AC drives, most DC drives rely on impedance to provide isolation and this has limitations, according to Control Techniques.

The thyristors used in DC drives are the most common point of failure. Those used in the new drives are protected against over-voltages during switching and are designed to survive lightning-induced surges of up to 6kV.

As well as a built-in field controller, there is the option of an external field controller rated at up to 25A for dynamic applications such as rapid reversing. For larger motors drawing bigger currents, a special mode allows the drive itself to act as a field controller. 

The Mentor MP covers the current range 25–1,850A using single modules, and up to 7,400A if the modules are paralleled. It is available in 12- or 24-pulse configurations. The drives have the same footprint and power connections as the earlier Mentor II drives, allowing direct replacement. Software wizards help to migrate from an old drive to a new one, and to set up the drive with its motor.

CT produced the world’s first digital DC drive in 1984. According to Sewell, the company has been increasing its DC sales and share of the DC market every year. “DC is in the DNA of Control Techniques,” he declares. In 2007, the company held an estimated 13% of the $370m global DC drives market and Sewell hopes that the Mentor MP will boost this share to 18% by 2012.