Most power- or control-switching applications provide both manual and remote operator control capabilities. For these remote switching functions, D.C. motors serve a vital role as remote motor operators. Two remote control applications that employ DC motors are circuit switchers in electrical transmission and distribution substations in the utilities industry and rail track switches in the transportation industry.

Electrical Power Circuit Switchers

An electrical utilities substation is a high-voltage electric facility that’s used to switch, connect, or disconnect generators, equipment and other circuits in or out of service throughout a power grid. There are four types of electrical substations: Step-Up, Step-Down, Distribution and Underground Distribution Transmission Substations. ¹ In these applications, circuit switchers are used to switch A.C. voltages up to 1100kV, and D.C. voltages up to 500kv. ²

Circuit switchers are electro-mechanical assemblies typically consisting of an interrupter sub-assembly, disconnect switch, fault sensing & protection, and a motor operator. The motor operator is used for remote switching or when the “disconnect switch’s function is integrated into a comprehensive system monitor and performance scheme such as a supervisor control and data acquisition system (SCADA).” ³

The motor operator is commonly a permanent magnet DC motor (brushed or brushless) that has a high torque, torsional output. The motor is typically a NEMA-rated, 48 VDC or 125 VDC, D.C. motor with features that can include permanently greased ball bearings, overload protection and dynamic braking. The motor operator “can be powered either via a substation battery source or via the input from an auxiliary AC source.” ⁴ For multiple switching operations, some motor operators “have their own internal batteries that can be fed from an auxiliary A.C. source via an A.C. to D.C. trickle charger for emergency operations in the event of loss of auxiliary AC power supply.”

Railroad Track Switches

Railroad switching is integral to the safe and normal operations of railroad transportation. It entails the manual or remote movement of switch rails, which are laterally moved from one position to another in order to change a railway junction point or spur so railway traffic can progress on its scheduled course.

The rail switching function can be accomplished manually or remotely. Manual, rail switching is performed by an operator at the railroad switch who moves a lever, rail operator or a hand pump to change the rail track’s position. Remote operation is performed via a track switch machine that is computer controlled remotely. This computer controller can sense when a train is on a specific length of rail track, provide warning signals, and initiate a rail switching operation by energizing an electric motor that drives the track from one position to another. ⁵ The track switch, drive motor is commonly a brushless, permanent magnet DC motor. “The controller has control circuitry for energizing and de-energizing field coils of the [brushless D.C.] motor sequentially as the armature rotates.” ⁶

Another type of rail switch machine is the electro-hydraulic rail switch. This type uses an electro-hydraulic power pack to provide the force to move the switched rail. The hydraulic power pack includes a manifold, control valves, pressure switch, pump and DC electric motor. The moving force is provided by a hydraulic cylinder, including a position transducer that provides feedback to control the movement of the cylinder or actuator. This rail switching type can be powered from a D.C source, a battery bank or solar cells for rail switch operations even in remote areas. In case of a loss of electrical power, a hand pump is available to manually switch the rail. ⁷

Forklifts are manufactured with varied designs, power sources, load capacities, and lifting configurations for both industrial moving and material handling applications. ¹ Forklift trucks are classified into two broad categories: indoor and outdoor use. Outdoor-use forklifts are powered by an internal combustion engine fueled by either gasoline, diesel, LP gas or CNG gas. Indoor-use forklifts ² are powered by an electric motor (12, 24, 36, or 48 VDC) and typically use large lead-acid batteries (10-75KWh capacity) for traction, steering and lifting power; the batteries also function as a counterweight to provide a counterbalancing force to oppose the lifted load in order to maintain stability of the forklift. ³. The forklift’s lifting mechanism is electro-hydraulically powered and consists of a fork, mast and lift/tilt jacks or cylinders. A hydraulic pump driven by an electric motor “forces hydraulic fluid through control valves. Hydraulic pressure raises the lift jack, which raises the fork by means of a system of chains and rollers. The forks raise on a mast. Heavy loads can be tilted backward by the tilt jacks to aid in stability. The lifting capacities of electric forklift tracks range from 1,000 to 10,000 pounds.” ⁴

Types of Electric Forklifts

Electric forklifts typically include walkie/rider pallet trucks and sit down, counterbalanced forklift trucks. There are two main types of electric, motorized pallet trucks: walkies and riders. Walkies can handle heavy loads for short distances. They are less expensive than riders. Since they move at walking speed, collisions when they do occur are less severe. Riders are used for long distances that would make a walkie impractical. Due to their fast speeds, they can pose a safety hazard to both the operator and pedestrians within the vicinity of operation. High lift pallet trucks are a variation of walkies and riders. They are used to move material on warehouse shelving that’s beyond the reach of most workers. High lift pallet trucks can be unstable since the center of gravity changes as the load height is increased, so it is critical to only lift loads within the manufacturer’s specifications. ⁵

Sit-down, counterbalanced forklift trucks are the most popular type of industrial & material handler. Similar to the fork-mast design of most pallet trucks, sit down forklifts have a place for the operator to sit that’s located between the lifting mechanism and the battery located in the rear of the machine. Fast speed and instability are the two main safety hazards of sit-downs. Order picker forklifts are used to obtain material on shelving while straddle forklifts are used to carry long material typically used in construction (pipers, boards, etc.) ⁶

Uses of DC Motors in Forklifts

Permanent magnet DC (PMDC) Motors ⁷ use a strong, permanent magnets to produce the motor’s magnetic field. Due to this constant magnetic field, PMDC motors are characterized by a consistent speed-torque response over the motor’s operating range (up to base speed). They are more compact and efficient with better thermal characteristics than wound-field DC motors so they can be used for continuous duty applications. But they have lower horsepower ratings than wound-fields; therefore, they are used in functions such as the steering (motor-pump) system and some lifting pump drive applications. In addition, PMDC motors have a lower stall torque than wound-field DC motors. Wound-field DC motors ⁸ use electromagnetic excitation to produce the motor’s magnetic field. When used in a series-field configuration, they have very high starting torque. They have high horsepower ratings so they can be used for high load applications at much higher speeds than PMDC motors. Typically, they will be used to power the traction drive, steering systems or the lifting system’s hydraulic pump drive. Their thermal characteristics make them most suitable for intermittent duty applications. DC motor control in electric forklifts is usually a voltage control, chopper system (DC-to-DC converter) using a buck/boost chopper circuit. ⁹

Hydraulic pumps are the workhorses used in nearly all industries including, construction, steel milling, mining, manufacturing, machining, heavy equipment, among others. They range from small pumps to hydraulic power packs for mobile applications to large hydraulic pumps used in the petroleum industry for pumping crude oil. Material handling, lifting and traction drives are some of the most popular applications.

By definition, a pump uses the mechanical input of a prime mover and converts it into pressurized fluid power to perform work. The prime mover can be a diesel or gasoline engine. But for electro-hydraulic pumps, the prime move is an electric motor. ¹ D.C. motors have been used as pump drives for many decades because of their ease of variable speed control and “faster response in transient conditions.” ² The introduction of low-cost, brushless DC motors overcomes the higher maintenance of brushed DC motors. ³ This article will discuss the types of hydraulic pumps and motors used in pumping applications and the important factors to consider when sizing a DC motor for a hydraulic pump.

Pump Types

Hydraulic pumps are classified in two broad categories: rotodynamic (centrifugal) and positive displacement. Centrifugal pumps employ a rotating impellor that uses centrifugal force to drive fluid from the inlet to the discharge side of the pump. There are many sub-categories of centrifugal pumps based up their specific application. Common types of centrifugal pumps include submersible, priming, and axial flow. Positive displacement pumps are the other broad category of hydraulic pumps. These pumps typically use gears, vanes, diaphragms or pistons to force a fixed amount of fluid through the inlet to the discharge side of the pump. Common types of positive displacement pumps are gear, rotary vane, screw, axial piston, diaphragm, plunger, radial piston, and peristaltic. Some pumps don’t fit directly into the two broad pump categories. These form a special category that includes ejectors, hydraulic-ram, air-lift and contraction pumps. ⁴

Types of DC Motors in Pump Applications

DC motors have been used as pump drive motors due to their variable speed control ability, especially at low speeds, simple control system, high starting torque and good transient response. Brushed, wound-field DC motors have formed the primary type of DC motor used in pump applications for many years. But permanent magnet (PMDC) and brushless DC motors have seen greater adoption rates, primarily due to their simple and compact design, high efficiency and power density, a wide range of frame sizes, and their need for less maintenance.

PMDC motors obtain their magnet field from strong permanent magnets, instead of electromagnets, which provide improved thermal properties and a constant magnetic field under all operating speeds and transients. Permanent magnet motors perform similar to shunt field-wound motors but they generally have more speed fluctuations during load changes. The permanent magnets give this type of motor excellent thermal properties that permit it to be used for continuous duty applications. Applications that require higher ‘part load’ efficiency at lower speeds is a typical application of PMDC motors.⁵

Despite the increased maintenance of brushed, wound-field DC motors, these motors possess distinct advantages that have made them the mainstay as pump drives for many decades. ⁶ Commonly operated in a series-field configuration, these wound-field motors have very high starting torque and can operate at high speeds. However, since they are load dependent, their output speed varies with the applied load. But they can generate very high power for short time periods. They are often used in pump applications with higher loads operated at higher speeds with an intermittent duty cycle.

Brushless DC motors have seen a quick adoption because they overcome the problem of brush maintenance common to brushed DC motors. ⁷ They characteristically have no brush sparking, high operating speeds, high efficiency, a compact size, and a fast response. ⁸

Pump Motor Sizing

Selecting and sizing a DC motor for a hydraulic pump application requires an understanding of the characteristics of both the motor and the pump. These factors assist in matching the motor’s horsepower (HP), rated full load current (FLA) and torque specifications to the pump’s flow, volumetric efficiency at the desired pressure and speed range, based upon pump performance curves provided by the manufacturer. ⁹ Pump motor selection is dependent upon a variety of factors including load and torque requirements, drive ratio, operating environment, efficiency, frame size, mounting configuration, enclosure type, battery amp/hour draw for mobile pump applications, among others. ¹⁰ Ensure the motor has both the capacity to drive the pump and desirable speed/torque characteristics. ¹¹ Motors operate most efficiently when fully loaded so avoid oversizing or undersizing the motor. Additionally, a motor’s amperage depends on the specific gravity of the fluid being pumped; therefore, the motor should be tested with a fluid that’s similar to the actual fluid to be pumped. ¹² The service factor should be taken into account during motor sizing calculations. The service factor is the overload capacity that a motor possesses without insulation damage occurring. The NEMA standard service factor for totally enclosed motors is 1.0, where there is no overload capacity. However, service factors range from 1.0 to 2.5, with 1.15 being the most common. See the motor manufacturer’s specifications for details. ¹³ The duty type affects motor sizing because it depends on how the pump will be operated. Duty types include: continuous, short time, and intermittent periodic-duty. Operating a motor not designed for a specific duty type can cause irreversible damage to the motor. ¹⁴

There are many factors that affect the life expectancy of an AC induction motor (or any electric motor). These factors can include input power problems, improper mechanical installations, malfunctions in the load, environmental factors, among others. Assuming that the motor is being operated under normal conditions, sized correctly for the application and within the manufacturer’s design requirements, it can last 15 years or more. ¹ However, rewinding a motor usually is the result of a catastrophic failure in the motor’s insulation and windings and is usually due to a thermal breakdown. Hence, generally speaking, a motor that requires rewinding may not have been operated under normal conditions. Motors are frequently replaced rather than rewound due to costs, convenience and the claim that rewinding may reduce the motor’s efficiency. ² Early failure of motor bearings is usually the result of improper mechanical installation causing undesirable forces acting on the bearings, or simply poor maintenance. Bearings should be inspected regularly for lubrication and uncharacteristic noises. Their life expectancy depends on factors previously cited. ³ Motor vendors typically recommend bearing replacement every two years. Refer to the motor manufacturer’s specifications for specific information.

Electrical motor torque is proportional to the product of magnetic flux and the armature current. Mechanical or load torque is proportional to the product of force and distance. Motor current varies in relation to the amount of load torque applied. When a motor is running in steady state, the armature current is constant, and the electrical torque is equal and opposite of the mechanical torque. When a motor is decelerating, the motor torque is less than the load torque. Conversely, when a motor is accelerating, the motor torque is higher than the load torque. ¹

The infographic explores the various areas that can lead to electric motor failure, including bearings, stator windings, external conditions, rotor bar, shaft coupling, and external conditions.

You can reduce the risk of failure by ensuring your electric DC motors are maintained properly. Be sure to read our General Guide to DC Motor Maintenance for tips and solutions to ensuring your electric motors run a top performance.

Source: L&S Electric

The term “quality” has many meanings. Most of the time, it is defined in subjective terms such as, exceeding expectations, or, in more casual terms, like “doing the job right the first time.” While it’s true that a quality product should exceed a customer’s expectations and be manufactured correctly, these definitions of quality are generic and subjective, especially for a motor manufacturer who has long-term relationships with its customers. At a DC motor manufacturer such as Ohio Electric Motors, quality is defined more aptly in objective and measurable terms. Specifically, quality is defined through the processes used to produce DC motors. Since manufacturing processes can be defined, controlled and measured to an objective standard, the “quality” of a DC motor is one that is produced as close as possible to that standard.

These processes are not limited to the manufacturing operations performed on the shop floor. Quality processes of a DC motor manufacturer extend throughout the supply chain and include the design processes as well as the performance of documented production tasks. Ohio Electric Motors has integrated several quality systems that provide a checks-and-balances “gauge” to verify that its custom designed DC motors are produced by standardized processes that stamp “quality” on each an every motor that leaves the plant. These systems include:

• The ISO 9000 Quality Management System
• The Lean Six Sigma Quality System
• Independent Product Safety Testing

The ISO 9000 Series Quality Management System

The ISO 9000 is a series of standards to manage the quality control processes of an organization. Published by the International Organization for Standardization, the standards are based on eight management principles that include, customer focus, process management, decision-making, supplier relationships, among others. The ISO 9000 standards have evolved over the years. Presently, Ohio Electric Motors is certified to the most current iteration of the series: ISO-9001:2008. OEM has taken advantage of the ISO 9000 quality management system to standardize the documentation of production procedures, the monitoring of supplier quality, and the implementation of a comprehensive testing program which includes 100% end of line testing and first piece inspections. Every motor that is produced by OEM is tested for peak performance and reliable operation.

The Lean Six Sigma Quality System

Lean Six Sigma is a business process management system that combines “Lean” management concepts and “Six Sigma” quality concepts to improve quality through process control and the reduction of process errors, defects and waste. The system emphasizes the continuous improvement of processes. Ohio Electric Motors has been a Lean Six Sigma company for many years. It uses Lean Six Sigma to achieve bottom line results such as, improving operational processes, identifying problems and solutions quickly and systematically, and reducing waste & cycle time.

Independent Product Safety Testing

Quality products are safe products that can measure up to independent testing. To verify the safety of its products, Ohio Electric Motors uses independent testing organizations such as, Underwriters’ Laboratories (UL), to independently test the entire line of its custom design, made-to-order DC motors. All of OEM’s motors are listed by UL and the CSA.

Most industry experts would agree that successful motor manufacturing requires significant competencies in design, manufacturing and quality assurance. No doubt these are crucial to the business success of a custom DC motor producer like Ohio Electric Motors. But OEM would add one other business competency into the success formula of a motor manufacturer: product support.

The real sign of a mutually beneficial, business partnership between a electric motor manufacturer and a customer is how the product is supported after it leaves the plant. While the goal of product support is total customer satisfaction, this term encompasses many different activities of the manufacturer-to-customer relationship that culminate in total product support. At OEM, product support is implemented in three separate but related support channels: Applications, Sales and Service.

Applications Support

As a critical, before-market support function, applications support is vital to matching as well as sizing a DC motor to an application. Motors are usually part of a complex electro-mechanical, motion control system, so knowing how the motor is going to be used and under what conditions is essential to promising a long service life. Product application issues addressed here are as varied as audible noise, bearing choices, vibration issues, torque-speed requirements, type of motor (brushed/brushless), EMI/EMC compliance and the operating environment. Since OEM specializes in custom designed, built-to-order, DC electric motors, our engineering staff is highly proficient with applications support.

Sales Support

If there were a motto that OEM would use to describe our philosophy regarding sales support, it would be “Sell and Support Locally.” Nowadays, business relationships can be started or facilitated by technology, but are only sustained by local, sales and support professionals. OEM has built a local network of sales engineers who meet with customers in their offices or at their facilities every day of the week. We have sales offices in all 50 U.S. states plus Canada, with a few states having more than one sales office, such as CA, IL, IN, NV, NY, OH and PA. These sales representatives provide before- and after-market sales support to our customers. Local contacts and relationships are integral to OEM’s core business: custom DC motor design and manufacturing.

Service Support

In any business, customer service is the first line of support to a customer. But OEM has structured its customer service department as much more than a call center or a place to order spare parts. Staffed with factory-trained professionals, our representatives are service support experts. Many of them have held different roles in motor manufacturing so they can speak from the viewpoint of a manufacturer, a service provider and an end-user. Personable, flexible and knowledgeable, they can take a customer through the steps of resolving a problem in short period of time. We know that many of our motors are installed in production applications so resolving their problems promptly is critical for eliminating lengthy equipment downtimes. In addition, we offer in-house testing and repair services for our line of motors with fast turnaround times at a reasonable price for non-warranty repairs.

Most businesses describe their devotion to customer satisfaction as a prime benefit of their products and services. Yet, in the business press, surveys of customer satisfaction often reveal this devotion is not always a reality. Too often customer service is compartmentalized to the call center as an after-market business process. We at Ohio Electric Motors approach customer service in a much different way. For OEM, customer service is synonymous to motor quality and is integrated into engineering, production, and order fulfillment using a four step system:

• Analysis of Customer Needs
• Planning for the Accomplishment of Goals
• Implementing the Project
• Evaluating our Customer’s Requirements

Analysis of Customer Needs

The production of quality DC motors is a complex task that requires a cross-functional team of professionals. The first task our team takes on is first analyzing the customer and determining what he needs. This task ensures that what is produced by OEM really answers our customers needs, which is the first step in the long road of integrating customer service into our motors. After determining what our customers need, our team analyzes what we need to do, as far as our organization, our suppliers and our processes, in order to move the project forward. We then address what our performance processes, such as, benchmarks and metrics. This period of analysis is an on-going process that is revisited throughout the development and production project and forms the first step of integrating customer satisfaction into our products.

Planning for the Accomplishment of Goals

It’s one thing to say you are a customer-focused organization and another to make it a reality that a customer perceives as such. Ohio Electric Motors uses an in-depth planning phase to establish the priorities, mission objectives and roles & responsibilities of each member of our organization. This is perhaps the most involved step of our approach to customer service. Our planning process is much more than an extended management strategy session. Rather, it establishes the project’s organizational structure, resources, training needs (if applicable), project management systems, risk assessments, budgets & cost accounting and supply chain management. Finally, we conclude the planning phase with ways to kick-off the project and build team cohesion. We want our employees to believe in the job they are about to do. And OEM management wants to empower them do the best job possible. When our workers believe they “own” the job, what happens is they improve the quality of the electric motors OEM produces, which is customer service by any other name.

Implementing the Project

A successful planning phase leads to a rapid and efficient implementation of the electric motor manufacturing project. This where we take all the things we learned while analyzing our customers needs and planning for the project and make them a reality. Throughout the implementation phase we are comparing what we thought was necessary for a successful project to what is happening in real-time on the engineer’s CAD station and all the way to the activities on the shop floor. We monitor how our resources are being used. We address problems, conflicts and changes, so we can take immediate corrective action. This is where engineering and production quality meets customer service even before our motors are shipped.

Evaluating Our Customer’s Requirements

The conclusion of our successful project analysis, planning and implementation phases is the final step: evaluating our results relative to customer satisfaction and requirements with quantitative methodologies. We develop reports to document costs, performance and the testing of our motors. We conduct process reviews and meet to see how we can improve them. This type of checks-and-balances evaluation tries to close any gaps, so to speak, and verify that what we are producing is what our customers want. This is the endgame for Ohio Electric Motors: DC electric motors built with quality and answer the requirements of our customers.

If you are an original equipment manufacturer who needs the services of a DC motors manufacturer who can design, build and test custom DC motors, what factors should guide your decision on whom to select? A basic starting point is investigating the manufacturer’s capabilities in design, manufacturing and its ability to deliver on schedule. As a successful, custom DC motor manufacturer nearly 100 years, Ohio Electric Motors has found three important requirements for a custom motor manufacturer to possess to ensure a profitable business partnership: (1) a professionally trained design and manufacturing team, (2) comprehensive manufacturing facilities and (3) standardized work processes verified by quality control systems.

Professionally Trained Engineering and Manufacturing Team

Producing custom-made, DC motors is a complex process. Even before the raw materials are trucked to the manufacturing plant and brought to the production line, both the client and electric motor manufacturer have started to solidify their working relationship by laying the ground work that’s required prior to the commencement of production. Successful working relationships require trained professionals, including engineering, manufacturing, supply chain, logistics, quality control, among others, to create not only the motor design and prototypes, but also the manufacturing processes and delivery channels. Ohio Electric Motors has built a design and manufacturing team of highly trained and customer-focused professionals. It leverages both the technical expertise and customer service skills of its staff to ensure production goals occur within budget.

Comprehensive Manufacturing Facilities

Manufacturing any product requires both the equipment and facilities to handle projected production volume, capacity or throughput. Beyond capacity considerations, what’s key for a custom electric motors manufacturer is to have all the machinery, equipment and testing capabilities in house and on-site so it can produce motors from start to finish in a timely fashion. Ohio Electric Motors has built a state-of-the-art comprehensive production facility that’s fully equipped to manufacture even high volume runs. It’s onsite process equipment includes, CNC machining, shaft splining, automated magnetizing, heat treating, epoxy coating insulation, automated coiling, winding, commutator slotting and balancing, varnishing and welding/painting/special fabrication. It also has a testing laboratory, which includes a 30 HP dynamometer and 500 Amp testing capability, to conduct both standard and special tests.

Standardized Work Processes Verified by Quality Control Systems

One of the motivations for using a custom motor manufacturer is the belief that a specialist can manufacture a motor, quicker, less expensively and with a greater level of quality. And it is the ability to manufacture a quality product that reaps both cost and time benefits. To obtain a high level of quality, a successful DC motor manufacturer should implement standardized work processes to enhance consistency and reliability. In addition, the motors should be tested throughout the production chain to verify this quality. Ohio Electric Motors understands the vital importance of manufacturing process control to produce consistent and reliable product. That’s why it has invested in ISO-9001: 2008 registration and implemented Lean Six Sigma initiatives. All of its machining operations undergo first piece inspections and all of its motors go through end-of-line testing. It uses documented manufacturing procedures and its production work-stations are linked to the engineering department to ensure all parts are manufactured to the latest revisions.