Download Lab 42 Electric Motors and Generators

LAB 42: EFFICIENCY OF MOTORS AND GENERATORS
Tuesday, April 15, 2014
OVERVIEW
Electric Motors and generators play an important part in our industrial society. We find
many types of motors and generators used in homes, schools, factories, and offices.
Generators are most often used in power plants. Motors are more common, being used in
many electrical tools and appliances.
The main parts of generators and motors are very similar to one another. They differ
only in how they are used. Electric motors and generators are devices that convert power
from one form to another. Generators convert rotating mechanical power to electrical
power. Motors convert electrical power to rotating mechanical power.
The power input (PIN) to a motor or generator is the product of the voltage and current
input. The power output (POUT) of a motor or generator is the product of the voltage and
current output. This is shown in the equation P = V  I.
Recall that linear power can be expressed as the product of force and velocity. Rotational
power may also be expressed in the convenient form P =   .
The efficiency of a motor or generator is equal to the ratio of output power to input
power. This is given in the equation below:
Efficiency =  =
Pout
x 100%
Pin
In this experiment you will study the hookup and operation of DC motors and generators.
For information and not part of this experiment there are two basic types of DC motors
and generators, series-wound and shunt-wound. Each of these motors has a special
purpose or use.
The series-wound motor has its field windings connected in series with the armature
windings. The field windings in a series-wound motor are a few turns of large diameter
wire. This causes the motor to have high torque output. Speed regulation is not good,
but series-wound motors can handle heavy loads.
The shunt-wound motor has its field windings connected in parallel with the armature
windings. The field windings in a shunt-wound motor are many turns of small diameter
wire. This motor has low torque output, but very good speed regulation. It is used where
constant speeds are important. It runs at a higher speed than a series-wound motor for a
given source voltage.
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LAB 42: EFFICIENCY OF MOTORS AND GENERATORS
Tuesday, April 15, 2014
OBJECTIVES
A) Measure the electrical power used to operate a DC motor.
B) Find the electrical power produced by a generator driven by an electric motor.
C) Find the efficiency of a motor-generator assembly.
EQUIPMENT REQUIRED
Mechanical Breadboard
Universal Lead Set
DC Motor (2)
Circuit Panel Easel
Digital Multimeter (DMM)
Lamp #53 with mounted base
Shaft Coupler Package
Allen Wrench Set
Circuit Panel
AC/DC Power Supply
Analog Multimeter (VOM)
PROCEDURE
A) Lab Setup: The set up for this experiment is shown in Figures 1 and 2. Refer to these
figures when assembling your equipment.
1. Mount the two DC motors on the mechanical breadboard using the shaft coupler kit to
couple the motors. Make sure that the height of the motors is the same.
2. Connect the left DC motor to the 0-24 VDC power supply. See figure 2. Insure that the
power supply is off and the voltage adjust is at minimum.
3. Connect the DMM as an ammeter between the DC motor/generator and the lamp.
Select the 2 ampere DC range. See figure 2.
4. Connect the second terminal of the DC motor/generator to the second terminal of the
lamp. See figure 2.
5. Connect the VOM across the lamp as shown in figure 2. Select the 15 volt range.
6. Before turning on the power supply, insure the voltage adjust control is at minimum or
completely CCW.
COLLECTING DATA
B) Measuring the motor input and generator output power
1. Set the power supply to measure 0-24VDC and then turn it on. Adjust the voltage to 3
VDC.
2. Push the AMPS/VOLTS button on the power supply to measure DC current in
amperes. Read the power supply display and record your results in Data Table 1. Read
and record the generator output voltage and current in Data Table 1.
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LAB 42: EFFICIENCY OF MOTORS AND GENERATORS
Tuesday, April 15, 2014
3. Release the AMPS/VOLT button on the power supply. Adjust it to 4 VDC.
4. Repeat step B-2.
5. Release the AMPS/VOLT button on the power supply. Adjust it to 6 VDC.
6. Repeat step B-2.
7. Turn off the power supply. Proceed to the next section.
CALCULATIONS
C) Finding the power in and out and efficiency of the Motor-Generator Assembly.
1. Find the input power for input voltages of 3, 4, and 6 VDC. Use the formula below and
values from Data Table 1. Record your answers in Data Table 2.
𝑃𝐼𝑁 = 𝑉𝐼𝑁 · 𝐼𝐼𝑁
2. Find the output power from the generator for each value of input voltage to the motor.
Use the values from Data Table 1 and the equation below.
𝑃𝑜𝑢𝑡 = 𝑉𝑜𝑢𝑡 · 𝐼𝑜𝑢𝑡
3. Find the efficiency of the motor-generator set for each value of input voltage to the
motor. Use the equation below. Enter your answers in Data Table 2.
% 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 = (
𝑃𝑜𝑢𝑡
) 𝑥 100 %
𝑃𝐼𝑁
4. Complete the analysis section of your lab report.
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LAB 42: EFFICIENCY OF MOTORS AND GENERATORS
OBJECTIVES:
Tuesday, April 15, 2014
SKETCH:
DATA TABLE 1
MOTOR
Input Voltage
(V)
MOTOR
Input Current
(A)
GENERATOR
Output Voltage
(V)
GENERATOR
Output Current
(A)
Output Power
Pout
(Watts)
Efficiency
3 VDC
4 VDC
6 VDC
DATA TABLE 2
Motor Voltage
Vin
(VDC)
Input Power
Pin
(Watts)
%
3
4
6
SAMPLE CALCULATIONS:
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LAB 42: EFFICIENCY OF MOTORS AND GENERATORS
Tuesday, April 15, 2014
LAB 42 ANALYSIS
1. How are motors and generators the same? How are they different?
2. Explain the function of the motor in this experiment.
3. Explain the function of the generator in the experiment.
4. In a hydroelectric dam system, what provides the same function as the motor did in this
experiment? Be specific.
5. What caused the low efficiency for this experiment?
6. How would you design a more efficient system?
Use the 5-step method to solve the following problem.
7. A DC electric motor has an input of 12 A at 24 V. It rotates at 1200 rpm and
produces a force of 1.5 lb on a de Prony brake with a lever arm of 9.0 inches. Find the
efficiency of the motor.
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