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, Einstein 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. The most significant being difficult speed control and control complexity. An AC drive is not 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.

Maura Falk, Associate Editor, Industrial Maintenance & Plant Operations

Industrial Electronics: Repair or Replace – Weighing The Benefits

As a provider of high quality assessments and training to industry, MPACT Solutions is often asked whether repair or replacement is the best option when considering industrial electronics. With current economic conditions, the decision to repair your industrial electronics is more important than ever. Given the right repair company, the answer to this question should be an easy one. However, many manufacturers often needlessly replace expensive controls. Either because they are unaware of the cost benefits of repair or they may have dealt with a less than reputable repair company in the past.

Here are a few tips for making the right decision about repair versus replace:

Are there real cost savings?
Most maintenance managers know that a new Reliance PC board costs just under $3500, but are they aware the same unit can be repaired for approximately $700! An 80% savings over the cost of new! As another example, the cost of a new Allen Bradley 1394 servo motor can run as high as $2430 depending on its feedback device. These motors and feedback devices can be repaired and reconditioned for as little as $910, a 63% savings. True cost savings that add up quickly when choosing repair versus replace!

What is most convenient?
Steve, maintenance manager with a corrugated plant, had the following to say regarding repairs for his plant. “I have old equipment paired with new equipment and over the years our hardcopy parameters have been misplaced, software has been troublesome and modifications have been made. I know when TEAMSESCO returns my units, the jumpers I have installed will be in the correct place, my program will still be intact as well as my parameters. I can install the repaired unit in my machine and I am good to go.” Steve went on to say that when he is forced to buy new, his down time and cost are increased because he has to program drives and make sure the parameters are correct for his application, a time consuming task when reading the parameters off of a “20 year old piece of greasy paper!”


How do I find a quality repair partner?
There are many repair companies offering repair services on industrial electronics and servo motors. Just Google ‘servo system repair’ and see what you get! However, many of these companies are small operations with very limited capabilities and even less test equipment. When choosing a repair company we highly recommend touring their facility or at a minimum asking these five questions.

• How do you load test AC and DC drives?
• How do you test PLC’s?
• How do you test servo motors?
• What is your repair process?
• Explain your quality control process?

We asked Stuart Smith, president of TEAMSESCO, Industrial Technology Services, these same questions and below are the responses we recommend you look for when interviewing repair companies.

Q: How do you load test AC and DC drives?
A: Each of our AC and DC drive repairs are fully load-tested on our industry exclusive hydraulic loading system. We designed and built this load center in order to duplicate our customers’ application by using the drive to run a motor under full load and maximum amps. Our load center consists of 26 individual motors all under a hydraulic load, we are able to load-test drives much longer than any competitor using a simple dyno system. This allows us to find any common intermittent problems that other repair facilities might miss.

Q: How do you test PLC’s?
A: We test our PLC’s repairs using a compatible rack while running a series of programs. Each input/output module, or rack, is fully reconditioned and exercised before being released to the quality control department.

Q: How do you test servo motors?
A: Every servo motor is tested using the Mitchell system for alignment and checking the feedback devices. After the motor is repaired and fully reconditioned, we load test each motor using another load center custom built by our technicians.

Q: What is your repair process?
A: TEAMSESCO technicians repair each unit, but most importantly, they recondition it as well. We accomplish this by replacing all high failure rate components that we have documented over years of experience. Every unit is then load-tested, duplicating the customers’ on-site application as closely as possible.

Q: Explain your quality control process?
A: Each TEAMSESCO repair is backed by our StarService Guarantee and our QC procedure is tops in the industry. Every repair we make is approved by a senior technician that signs off on our 26-point inspection process. This inspection includes witnessing the final load test, insuring the unit’s cosmetics are reconditioned, that all common failure rate components are replaced and the general functionality of the unit is up to standard. This procedure gives our customers peace of mind and allows us to offer a 1-year warranty tracked by our state-of-the-art bar-coding system.

So what is MPACT Solution’s final analysis on repair vs. replace? If you find a repair company that performs quality, guaranteed work in a timely fashion and for a fair price we recommend you stay with them and develop a solid working partnership. Over time your partner repair facility will learn the unique needs that your plant has and will be able to expedite your repairs when you are in that inevitable down situation. Repairing your industrial electronics and servo system components will always be the right decision when you can demonstrate a viable cost and time savings by partnering with a reliable repair firm.


About TEAMSESCO: Since 1913 and through four generations of the same family’s dedicated leadership, TEAMSESCO’s core business has been in providing high-quality, repair services to manufacturing and other industries. As a founding member of EASA and with recognition as a National Star Service repair center, they continue to be one of the industry’s leading innovators. To learn more, call TEAMSESCO at 800-48-SESCO or visit them online at www.teamsesco.com.


About MPACT Solutions: MPACT Solutions offers a full range of customized consulting services. With over 150 assessment test and 250 online and hands-on classes to choose from, they are the number one resource for keeping your maintenance teams up-to-date and working at top efficiency. To learn more, call MPACT Solutions at 336-379-1444 or visit them online at www.mpactsolutions.com.

Reprinted with Permission from MPACT Solutions (www.mpactsolutions.com)