DC Motors and Drives

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 Siemens DC Drives

SIMOREG is the trade name for Siemens adjustable speed DC Drives. SIMOREG stands for SIemens MOtor  REGulator . Siemens DC drives are an important element of the TIA strategy. DC motors were the first practical device to convert electrical energy into mechanical energy. DC motors, coupled with DC drives such as Siemens SIMOREG 6RA70, have been widely used in industrial drive application for years, offering very precise control.

 KB Variable Speed DC Drives (SCR, PWM, Regen)

KB offers 47 models of off the shelf distributor style Variable Speed DC Drives that cover the most popular voltages and horsepower ranges. From 115/208-230 input voltages and extending from 1/100 to 5 horsepower, our DC drives are available as imbedded chassis/IP20, stand-alone Stamped Aluminum enclosures NEMA-1/IP40 and heavy duty, indoor/outdoor, wash-down die Cast Aluminum enclosures NEMA-4X/IP65. A variety of optional DC Drive accessories are also available to meet the most demanding applications.

KB Penta Power Variable Speed DC Drives are available through over 800 distributors worldwide.


Figure displays photo of some models of

KB DC drives courtesy of KB Electronics, INC

For more info refer to


DC Drives

DC SRC drives and motors remain common in industries such as metals, cranes, mining and printing. The current trend is to replace DC systems with new AC drives and motors to reduce maintenance overhead. This can, however, often be a significant task that requires the machinery to be taken out of service for an extended period while mechanical and electrical rework is completed.

Utilizing existing DC motors and upgrading the DC drives is often the most attractive option. DC motors are usually well built and capable of offering many more years of service to help lower project costs and minimize disruption and risks. Control Techniques DC drives are now based on our industry-leading AC drive technology to deliver enhanced motor performance, reliability and system integration options.

DC drives continue to be an attractive alternative for machine suppliers. The modern DC converters is easy to operate, compact and low in maintenance. DC Drives can be used in most industrial applications as well as for the modernization of old plants. ABB offers the complete portfolio of three-phase DC drives – from 9 kW (12 Hp) up to 18 MW (24 000 Hp). ABB DC drives are available directly from ABB or through valued ABB Drives partners.

 Mechanical Basics

Before discussing DC drives, it is necessary to understand some of the basic terminology associated with the mechanics of DC drives operation. Many of these terms are familiar to us in some other context. Later in the course we will see how these terms apply to DC drives.

 What is definition of Force?

Force is a quantity that is measured using the standard metric unit known as the Newton. A Newton is abbreviated by an “N.” To say “10.0 N” means 10.0 Newton of force. One Newton is the amount of force required to give a 1-kg mass an acceleration of 1 m/s/s. Thus, the following unit equivalency can be stated:

A force is a vector quantity. As we know already, a vector quantity is a quantity that has both magnitude and direction. To fully describe the force acting upon an object, you must describe both the magnitude (size or numerical value) and the direction. Thus, 10 Newton is not a full description of the force acting upon an object. In contrast, 10 Newton, downward is a complete description of the force acting upon an object; both the magnitude (10 Newton) and the direction (downward) are given.

Because a force is a vector that has a direction, it is common to represent forces using diagrams in which a force is represented by an arrow. Such vector diagrams. The size of the arrow is reflective of the magnitude of the force and the direction of the arrow reveals the direction that the force is acting. (Such diagrams are known as free-body diagrams.) Furthermore, because forces are vectors, the effect of an individual force upon an object is often canceled by the effect of another force. For example, the effect of a 20-Newton upward force acting upon a book is canceled by the effect of a 20-Newton downward force acting upon the book. In such instances, it is said that the two individual forces balance each other; there would be no unbalanced force acting upon the book.

When forces are applied in the same direction they are added. For example, if two 4 and 7 lb forces are applied in the same direction the net force would be 4 +7 = 11 lb.

See figure 2.


Figure 2

If a 7 lb of force were applied in one direction and 2 lb of force applied in the opposite direction, the net force would be 5 lb and the object would move in the direction of the greater force. See figure 3.


Figure 3

If 5 lb of force were applied equally in both directions, the net force would be zero and the object would not move. See figure 4.


Figure 4.

 What is definition of Torque?

Torque, moment or moment of force (see the terminology below), is the tendency of a force to rotate an object about an axis, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist to an object. Mathematically, torque is defined as the cross product of the lever-arm distance and force, which tends to produce rotation.

Loosely speaking, torque is a measure of the turning force on an object such as a bolt or a flywheel. For example, pushing or pulling the handle of a wrench connected to a nut or bolt produces a torque (turning force) that loosens or tightens the nut or bolt.

The symbol for torque is typically τ, the Greek letter tau. When it is called moment, it is commonly denoted by M.

The magnitude of torque depends on three quantities: the force applied, the length of the lever arm connecting the axis to the point of force application, and the angle between the force vector and the lever arm. In symbols:



τ is the torque vector and τ is the magnitude of the torque,

r is the displacement vector (a vector from the point from which torque is measured to the point where force is applied),F is the force vector,

× denotes the cross product,

θ is the angle between the force vector and the lever arm vector.

The length of the lever arm is particularly important; choosing this length appropriately lies behind the operation of levers, pulleys, gears, and most other simple machines involving a mechanical advantage.

Torque is the force that produces rotation. It causes an object to rotate. Torque consist of a force acting on distance. Torque, like work, is measured is pound-feet (lb-ft). However, torque, unlike work, may exist even though no movement occurs.

To calculate torque, apply this formula:

T = F x D

T = torque (in lb-ft)
F = force (in lb)
D = distance (in ft)

Figure 5

Full-load torque is the torque to produce the rated power at full speed of the motor. The amount of torque a motor produces at rated power and full speed can be found by using a horsepower-to-torque conversion chart. When using the conversion chart, place a straight edge along the two known quantities and read the unknown quantity on the third line.

To calculate motor full-load torque, apply this formula:

T = [HP x 5252] / rpm

T = torque (in lb-ft)
HP = horsepower
5252 = constant
rpm = revolutions per minute

For more information on torque:


What is definition of Speed?

 Speed is a scalar quantity that refers to “how fast an object is moving.” Speed can be thought of as the rate at which an object covers distance. A fast-moving object has a high speed and covers a relatively large distance in a short amount of time. Contrast this to a slow-moving object that has a low speed; it covers a relatively small amount of distance in the same amount of time. An object with no movement at all has a zero speed.

Speed = (distance) ÷ Time

 Linear Speed

 Linear path refers to the plain path like a straight road. You could often be walking, riding, running in a straight line road. The speed you are carrying is what linear speed is!

 Angular Speed

 In physics, the angular velocity is defined as the rate of change of angular displacement and is a vector quantity which specifies the angular speed (rotational speed) of an object and the axis about which the object is rotating.


 Acceleration is a vector quantity that is defined as the rate at which an object changes its velocity. An object is accelerating if it is changing its velocity.

Law of Inertia (Newton’s first law of motion)

An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.


Frictional resistance to the relative motion of two solid objects is usually proportional to the force which presses the surfaces together as well as the roughness of the surfaces. Since it is the force perpendicular or “normal” to the surfaces which affects the frictional resistance, this force is typically called the “normal force” and designated by N.


 Work refers to an activity involving a force and movement in the direction of the force. A force of 20 Newton pushing an object 5 meters in the direction of the force does 100 joules of work.

W = F × d = 20 × 5 = 100 joules


Power is the rate of doing work or the rate of using energy, which are numerically the same. If you do 100 joules of work in one second (using 100 joules of energy), the power is 100 watts.

Power = Work ÷ Time = 100 ÷ 1 = 100 watts


The story goes that Watt was working with ponies lifting coal at a coal mine, and he wanted a way to talk about the power available from one of these animals. He found that, on average, a mine pony could do 22,000 foot-pounds of work in a minute. He then increased that number by 50 percent and pegged the measurement of horsepower at 33,000 foot-pounds of work in one minute. It is that arbitrary unit of measure that has made its way down through the centuries and now appears on your car, your lawn mower, your chain saw and even in some cases your vacuum cleaner.

In short, power can be expressed in foot-pounds per second, but is often expressed in horsepower (HP). This unit was defined in 18th century by James Watt.

Calculate the horsepower. Using the formula HP=(RPM * T) / 5252, determine your automobile’s effective horsepower.

Example: A Porsche 911 generates 480 lb-ft. of torque at 2,500RPM. Expressed in terms of the equation, that is HP = (2500 * 480) / 5252 = 1,200,000/5252 = 228.48hp

 DC Motors

A DC motor is a mechanically commutated electric motor powered from direct current (DC). The stator is stationary in space by definition and therefore the current in the rotor is switched by the commutator to also be stationary in space. This is how the relative angle between the stator and rotor magnetic flux is maintained near 90 degrees, which generates the maximum torque.

DC motors have a rotating armature winding (winding in which a voltage is induced) but non-rotating armature magnetic field and a static field winding (winding that produce the main magnetic flux) or permanent magnet. Different connections of the field and armature winding provide different inherent speed/torque regulation characteristics. The speed of a DC motor can be controlled by changing the voltage applied to the armature or by changing the field current. The introduction of variable resistance in the armature circuit or field circuit allowed speed control. Modern DC motors are often controlled by power electronics systems called DC drives.

The introduction of DC motors to run machinery eliminated the need for local steam or internal combustion engines, and line shaft drive systems. DC motors can operate directly from rechargeable batteries, providing the motive power for the first electric vehicles. Today DC motors are still found in applications as small as toys and disk drives, or in large sizes to operate steel rolling mills and paper machines.


Figure 6

 What is Totally Integrated Automation (TIA)

Totally integrated automation (TIA) is a strategy (philosophies/architecture) in the automation technology, which was developed since 1996 by Siemens Automation and Drives. This strategy defines the interaction of extensive single components, tool (SW) and the services (spare part service, etc.) to achieve an Automation solution. The interaction performs integration across the four automation levels of the automation pyramid:

Management level (Ethernet)

Control Level (Ethernet)

Process and Field Level (PROFIBUS-DP)

I/O Level (AS-I)

The consistency of TIA offers a simplification and cost savings to companies involved in the value chain (OEM, System integration planner and end customer).

Sub definition: automation is composed of the essentials of the drives (frequency converter + motor), a programmable logic control as well as a Panel to the visualization.

More information on this subject on the following link:


What are DC Drives?

A DC drive is a DC motor speed control system. It modifies the armature voltage or the field current in order to control the motor’s speed. There are various types of DC motors used for different electronic speed controls.

Adjustable speed drive (ASD) or variable-speed drive (VSD) describes equipment used to control the speed of machinery. Many industrial processes such as assembly lines must operate at different speeds for different products. Where process conditions demand adjustment of flow from a pump or fan, varying the speed of the drive may save energy compared with other techniques for flow control.

Where speeds may be selected from several different pre-set ranges, usually the drive is said to be adjustable speed. If the output speed can be changed without steps over a range, the drive is usually referred to as variable speed.

Adjustable and variable speed drives may be purely mechanical (termed variators), electromechanical, hydraulic, or electronic.

Figure 1 shows variable frequency drives, showing capacitors(top cylinders) and inductors attached which filter the regenerated power

Although AC motors and vector-control drives now offer alternatives to DC, there are many applications where DC drives offer advantages in operator friendliness, reliability, cost effectiveness, and performance. We will discuss applications latter in this course.


Figure 1

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Download PDFKey terms discussed on the download file:

 Siemens DC Drives, Speed = (distance) ÷ Time, Linear Speed , Angular Speed, Acceleration, Law of Inertia, Newton’s first law of motion, Friction,  Work, Power = Work ÷ Time = 100 ÷ 1 = 100 watts, horsepower, armature , Brushless DC motors, BLDC motors, brushed DC motors,  rotor and a stator, Induction AC motor, slotted or slotless, Rotor, permanent magnet, flux density , torque, Principles and Operation of Brushless, solenoid or relay, electromagnets formed by a conducting coil, EMF, Brushes, rotating Basic DC Motor, torque “ripple”, DC Motor, Separately Excited DC Motor, Self Excited DC Motor, Shunt Wound DC Motor, Series Wound DC Motor, Compound Wound Motor, Cumulative Compound DC Motor, Short Shunt DC, Differential Compound DC Motor, Short Shunt DC Motor,  DC Motor Ratings, Insulation Class, Base speed at rated load, Rated Armature Voltage, Rated field Voltage, Armature, Rated Load Current , Shunt, Series, Compound, Permanent Magnet, Enclosure, Horsepower (Hp), 1 hp = 746 watts, Field Economizing, shuting the field off is the prevention of condensation, DC motors insulation class, Armature Voltage, Inductive components ,magnetic field, flyback diode ,DC motor Torque, tangential velocity, Torque, Thyristor, silicon controlled rectifier or SCR,  ANODE ,CATHODE, P type and N type (PNPN), BT151, thyristors, Power Control,  pressure-control, liquid-level regulators, thyristors, Stud and disc,  SCRs, AN SCR ,Door Intrusion Indicator Circuit, SCR BT169 ,LED, SCR application circuit, AC to DC conversion by thyristor, An ac-dc converter, thyristor , converter valves, bi-directional thyristor valves, C-DC converters ,bi-directional thyristor valves ,DC drive Converter, The output of one thyristor is not smooth enough to control the voltage of, brushed DC motors, Reverse Armature polarity, Reverse field polarity, Dynamic Braking, Regenerative braking, Dynamic braking ,Plugging or reverse current braking , dynamic Braking (Rheostatic Braking), MOSFET, Reverse current braking , plugging, plugging of separately excited DC motor,

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