Detailed Description of a DC Generator

A generator is the opposite of a motor; while a motor turns electrical energy into mechanical energy, a generator does exactly the reverse. Unlike alternating current generators, which produce current that periodically changes direction, a DC generator produces unidirectional current.

Features

• All direct current generators include at the minimum a rotating coil of wire; a split ring (with two breaks in it) that rotates together with the coil; two stationary metal brushes that transfer current from the rotating split ring to the external circuit and magnets that generate a magnetic field. The magnets may be permanent magnets or electromagnets. The combination of split ring and brushes is called a commutator.

Function

• As the coil of wire turns in the magnetic field, the magnetic flux (the total number of magnetic lines of force) passing through the loop of wire changes, because the angle between the coil and the magnetic field is always changing. In keeping with Faraday's Law, this change in magnetic field creates a voltage in the coil of wire and thereby generates electric current.

Considerations

• In an AC generator the EMF (electromotive force) if plotted as a function of time is a smooth wave-shaped graph (a sine wave), where the EMF is sometimes positive and sometimes negative. In a DC generator, the EMF rises from zero to max and falls back to zero, but never becomes negative. Some DC generators use more than one coil to smooth out this bumpy wave pattern and produce a more constant current.

Parts of a Dynamo Motor.

A dynamo motor, also known as an generator, is a device that can convert mechanical energy into an electric current. The concept of the dynamo is often attributed to Michael Faraday, who discovered that moving a magnet around a closed electric circuit can induce an electric current to flow in it. Modern dynamos or electric generators are made of several components that are essential for their function.

Magnetic Circuit

• On a modern dynamo motor, the magnetic circuit is made of several parts that include an armature core, a yoke, an air gap, and poles. An armature core is composed of sheet steel with a blanking die and thin magnetic steel laminates. These laminated sheets are either welded or bonded together to keep them from splitting apart.

  The poles are either steel laminates or solid steel, and they have field coils that set up the magnetic fields in the machine. The top and bottom poles are also called a pole head and a pole shoe, respectively. These poles usually fan out and are designed to smooth the flow of air on the air gap. The yoke is the casing where the completed poles are mounted, and it provides the magnetic path between the poles.

Electric Circuit

• The electric circuit is made of an armature winding, a commutator, a field winding and brushes. The armature winding is made up of copper wires that are insulated from the armature core. In a dynamo motor, the armature winding receives the voltage generated by the motor. Armature windings are connected to the commutator. The commutator acts as the mechanical rectifier that converts AC voltage to DC voltage, and it's usually made of silver-bearing copper. The commutator conducts the current to an external circuit through the brushes.

Mechanical Support

• The mechanical support of a dynamo motor is composed of a shaft, a frame, end bells, and bearings. In most cases, the yoke and the frame are the same, and they are usually made of steel or aluminum that encases the whole dynamo motor. The armature is placed inside the frame by using a steel shaft supported by two lubricated bearings that can either be a ball, a roller, or a sleeve type. Once the armature is placed inside the frame, both ends of the frame are enclosed using the end bells. The end bells are usually made of the same material used on frames and yokes.

How to Assemble a Dynamo With a DC Motor?

Electric motors and power generators are often identical in design. An AC motor, for example, may also be used as an alternator. The major difference in function depends upon whether the device is used to generate electricity such as an alternator or generator, or whether electricity is applied to the device to do work.

A DC motor contains a device called a commutator. This device allows a DC motor to produce DC power without adding any other electronics to the motor leads. When force is applied to a DC motor's rotor, the DC motor will work as a DC generator, also known as a dynamo.

* Use the electrical pliers to cut two lengths of electrical wire, with each length being six inches long. Strip 1/2 inch of insulation from the ends of each wire segment.

* Place one end of the first wire on the motor's positive electrical terminal. Melt a small drop of solder to both the electrical terminal and to the end of the first wire. Smooth out the soldered joint with the tip of the soldering iron, making sure that the electrical joint is shiny and free of lumps. Use this procedure to solder one end of the second wire to the negative electrical terminal.

* Attach the crank to the rotor shaft on the motor.

* Turn on the multimeter and set the measurement scale to "Volts DC." Connect the red probe to the loose end of the first wire, which should be attached to the positive electrical terminal. Connect the black probe to the loose end of the second wire attached to the negative terminal.

* Turn the crank and observe the multimeter display. If the crank is turned slowly, the voltage will fluctuate greatly. However, if the crank is turned quickly, the voltage will stabilize.

What Is the Difference Bewteen an Alternator & DC Motor Generator?

Generators were used to power vehicles before the invention of the alternator. DC generators produce direct current while alternators produce AC, or alternating current. The process of changing AC to DC is called rectification.

Function

• In a DC generator the coil of wire called an armature spins in a magnetic field. In an alternator, the magnetic field is spun inside a coil of wire called a stator.

DC Generator Vehicle

• A generator spins its armature to create a current. However, at lower speeds the generator cannot make a current, so vehicles run by generators cannot charge or maintain battery power at idle.

  Commutator

  • The current in a generator’s armature is alternating current, or AC, so to change it or rectify it a device called a commuter must be used. Overall, the output becomes DC.

  Alternator Vehicle

  • All modern-day vehicles have an alternator. The alternator is similar to a generator but can charge the battery and support higher amperages for electronics.

  Diodes

  • In an alternator, diodes change AC current into DC current. The diode can also do this without any moving parts.

Differences Between AC and DC Electric Motors.

An electrical motor converts electrical energy into mechanical energy in the form of torque (rotational energy). There are two types of motors, direct current (DC) and alternating current (AC), which differ both in the type of electrical energy they use and how they generate torque. DC motors were invented earlier, but are less commonly used today. AC motors have a simpler design and are used in most appliances and industrial equipment.

Structure

• Both AC and DC motors contain two essential components: a stator and a rotor. An electrical current creates torque when it moves within a magnetic field, according to Faraday's Law. In a DC motor, the rotor receives a direct current and a commutator reverses the current as the rotor rotates in a stationary magnetic field created by a permanent magnet in the stator. In an AC motor, the rotor receives an induced alternating current, and the stator is an induced magnetic field.

Mechanics

• The advantage of DC motors is that you can easily adjust their speed simply by increasing the voltage. However, DC motors have a more complex design, requiring brushes to transfer energy to the moving parts and a commutator to periodically reverse the voltage. These parts will wear out over time due to friction and eventually need to be replaced. AC motors have a simpler design, but they work at fixed speeds and cannot operate at low speeds.

Usage

• Due to their variable speed, DC motors can be used for both low-power and high-power applications. However, due to their higher cost and need for replacement parts, they are typically only used to power devices that require a variable power input, such as hybrid cars and certain toys. AC motors are cheaper to make and are compatible with the majority of modern appliances which have an AC energy source.

How to Find Torque From HP ?

Horsepower and torque are measures of an engine's output. In automotive engines, torque closely corresponds to how much force an engine generates when you first step on the gas, while horsepower gives an idea about how fast the car will go when you approach the rev limit, which occurs just before you must up-shift into the next gear. Automotive enthusiasts express this concept by saying that "torque gets you going and horsepower keeps you going".

* Get the horsepower for the engine and make sure it's expressed according to SAE standards, which stands for the Standard of American Engineers. If the horsepower is expressed in DIN units, which is more common on Europe, you'll need to convert by dividing the DIN horsepower by 1.0139.

* Multiply the horsepower by 5,252. When converting horsepower to torque, both figures depend on the speed at which the engine operates, which is expressed in revolutions per minute, or rpm. If you know the horsepower of an engine only at a particular rpm, you can calculate the torque figure for that specific engine speed only. If for instance, you are told that an engine makes 300 horsepower at 6,000 rpm and have no further information, you can use this data only to arrive at the engine's torque at 6,000 rpm.

* Divide the product from Step 2 by the rpm. The answer is your torque expressed in pound-feet. Returning to our original example, the torque figure would be 300 times 5,252 divided by 6,000, because the engine output was 300 horsepower at 6,000 rpm. The result will be 262.6 pound-feet. This is how much torque the engine generates at 6,000 rpm.

How to Convert HP to Torque ?

Torque represents a twisting force that causes an object to rotate, such as the force required to tighten a screw or to spin a wheel. In the imperial system of measures, which is used in the United States, torque is measured in foot-pounds. Usually torque refers to circular rotation, such as a spinning gear, but the rotation does not always have to be circular. To convert HP to torque, you also need to know the engine's number of rotations per minute.

* Look up the horsepower of your device in the owner's manual. This can be a car motor, water pump or any other mechanical device.

* Multiply the horsepower by the RPM at which your engine is turning, as in the following formula: HP*RPM. RPM stands for rotations per minute, and is shown on a tachometer, such as the one in a car. For example, if you have a 200 HP engine running at 2,500 RPM, you would multiply 200 by 2,500 to get 500,000.

* Divide the result from step 2 by 5,252 to calculate torque in foot-pounds.

The conversion factor of 5,252 is derived from one horsepower being equal to 550 foot-pounds per second; you have to multiply that number by 60 to convert from seconds to minutes (RPM means rotations per minute) and divide the result by 6.28, because there are 2π radians in a circle.

Finishing our example from the previous step, you would divide 500,000 by 5,252 to find the torque produced by a 200 HP engine running at 2,500 RPM, which equals about 95.2 foot-pounds of torque.