PASCO SE-8657 User Manual
Includes
Teacher's Notes
and
Typical
Experiment Results
MOTOR ACCESSORY
Instruction Manual and
Experiment Guide for the
PASCO scientific
Model SE-8657
012-06247A
8/96
© 1996 PASCO scientific $7.50
012-06247A Motor Accessory
T able of Contents
Section...................................................................................................... Page
Copyright and Warranty, Equipment Return................................................... ii
Introduction ......................................................................................................1
Equipment ........................................................................................................1
Table 1. Equipment Options for Experiments 1 - 4 ..........................................2
Operation .........................................................................................................3
Assembly—Motor Accessory onto the Variable Gap Magnet .........................4
Assembly—Motor Accessory onto the Coils and Cores Set ............................5
Suggested Uses ................................................................................................6
Experiment 1: Operation of the DC Motor......................................................7
Experiment 2: Operation of AC and DC Generators ....................................13
Experiment 3: Operation of an AC Synchronous Motor ...............................19
Experiment 4: Operation of the Universal Motor ..........................................25
Teacher’s Guide .............................................................................................29
Technical Support ..........................................................................................34
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Motor Accessory 012-06247A
Copyright, Warranty and Equipment Return
Please—Feel free to duplicate this manual
subject to the copyright restrictions below.
Copyright Notice
The PASCO scientific SE-8657 Motor Accessory
manual is copyrighted and all rights reserved. However, permission is granted to non-profit educational
institutions for reproduction of any part of the manual
providing the reproductions are used only for their
laboratories and are not sold for profit. Reproduction
under any other circumstances, without the written
consent of PASCO scientific, is prohibited.
Limited Warranty
PASCO scientific warrants the product to be free from
defects in materials and workmanship for a period of one
year from the date of shipment to the customer. PASCO
will repair or replace, at its option, any part of the product
which is deemed to be defective in material or workmanship. The warranty does not cover damage to the
product caused by abuse or improper use. Determination of whether a product failure is the result of a
manufacturing defect or improper use by the customer
shall be made solely by PASCO scientific. Responsibility for the return of equipment for warranty repair
belongs to the customer. Equipment must be properly
packed to prevent damage and shipped postage or
freight prepaid. (Damage caused by improper packing of the equipment for return shipment will not be
covered by the warranty.) Shipping costs for returning the equipment, after repair, will be paid by
PASCO scientific.
Equipment Return
Should the product have to be returned to PASCO
scientific for any reason, notify PASCO scientific by
letter, phone, or fax BEFORE returning the product.
Upon notification, the return authorization and
shipping instructions will be promptly issued.
ä
NOTE: NO EQUIPMENT WILL BE
ACCEPTED FOR RETURN WITHOUT AN
AUTHORIZATION FROM PASCO.
When returning equipment for repair, the units
must be packed properly. Carriers will not accept
responsibility for damage caused by improper
packing. To be certain the unit will not be
damaged in shipment, observe the following rules:
➀ The packing carton must be strong enough for the
item shipped.
➁ Make certain there are at least two inches of
packing material between any point on the
apparatus and the inside walls of the carton.
➂ Make certain that the packing material cannot shift
in the box or become compressed, allowing the
instrument come in contact with the packing
carton.
Credits
Author: Jim Housley
Editor: Sunny Bishop
Address: PASCO scientific
10101 Foothills Blvd.
Roseville, CA 95747-7100
Phone: (916) 786-3800
FAX: (916) 786-3292
email: techsupp@pasco.com
web: www.pasco.com
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012-06247A Motor Accessory
Introduction
The PASCO SE-8657 Motor Accessory transforms the
PASCO EM-8641 Variable Gap Magnet into a motor
that can operate on alternating or direct current, as well
as a generator that can produce alternating or direct
current. The Motor Accessory also transforms the
PASCO SF-8616 Coils and Cores Set into a universal
Equipment
The Motor Accessory includes
- armature with split commutator at one end and a
dual slip-ring commutator at the other
- brush holder
- shaft
- wrench/retaining nut
- maintenance items
motor. Combined with an AC/DC power supply and
sensors for voltage, current, and rotational speed,
these motors allow students to discover key concepts
and relationships concerning motors and electric
current. Students can also explore properties of AC
and DC generators with this apparatus.
dual slip-ring
commutator
armature
brushes
split ring
commutator
brush holder
- manual
- ceramic magnet
shaft
Additional Equipment Required:
- Variable Gap Magnet (EM-8641) or
- Coils and Cores Set (SF-8616)
wrench/
retaining nut
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Safety precautions
- Always wear safety goggles when in a room where the Motor Accessory is being used.
- Keep fingers and other objects away from the spinning armature.
- Choose power sources that limit current to not more than one ampere (1.0 A). The motor may overheat
if this current is exceeded or if power is applied continuously, especially if the armature is not rotating.
The motor is intended only for intermittent operation.
- Disconnect any power source whenever the motor is to be left unattended.
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Motor Accessory 012-06247A
➤ NOTE: Although the instructions for experiments in this manual are for mechanical setups
with specific PASCO equipment, the experiments in this manual may be set up in a variety of ways,
depending upon the equipment you have available. They can all be done with or without the
PASCO Science
experimental setups. You may be able to substitute other equipment for the PASCO models listed
Workshop computer interface. Table 1 lists the equipment suggested for optional
Table2.xls
in this table.
Table 1. Equipment Options for Experiments 1 - 4
Equipment Options
for Experimental
Setups with the
PASCO SE-8657
Motor Accessory
Experiment Options
Experiment 1: DC Motor
no computer interface
no computer interface
computer interface
computer interface
Experiment 2: AC/DC Generator
no computer interface
computer interface
Experiment 3: Synchronous AC Motor
no computer interface
computer interface
computer interface
Experiment 4: Universal Motor
no computer interface
computer interface
computer interface
Low Voltage DC Power Supply (SE-9720)
Motor Accessory (SE-8657)
Variable Gap Magnet (EM-8641)
xx x
xx x x
xx x x x x
xx x xx
xx x
xx xxx
xx x xx
xx x x x x
xx x xx x
xx x
xx x xx
xx x xx
(SE-9712) or similar*
Coils and Cores Set (SF-8616)
Low Voltage AC/DC Power Supply (SF-9584) *
Power Amplifier (CI-6550A) (CI-6552A)
Digital Function Generator/Amplifier (PI-9587)
Multimeter (e.g. SB-9623) or Ammeter (SF-9569)
Galvanometer (SF-9500) or Multimeter (SB-9623)
OR
Voltage Sensor (CI-6503)
Science Workshop 300 or 500 Interface
Science Workshop 700 or 6500 Interface
Digital Photogate Timer (SF-9215A)
Digital Stroboscope (SF-9211)
OR
OR
OR
OROR
OR
*If your power supply does not have the capability to quantify output current, you will need
to measure it using an ammeter, or preferably, by calculating it from the voltage drop
across a small value series resistor. (This option avoids the potential for damage to a
sensitive ammeter.)
It is important to limit the current to a maximum of 1 A to avoid
damaging the armature.
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012-06247A Motor Accessory
Operation
Options for electrical connections
- Banana-style plugs may be inserted into openings
in the ends of the black plastic brush holder.
- Large alligator clips may be attached to the brass
posts that hold the brushes.
- Small alligator clips may be attached directly to
the ends of the brushes where they protrude from
the slits in the brass posts.
Options for Power Sources
It is important to limit the current of the power source
to 1.0 A to avoid damaging the coils of the armature.
Either choose a power supply that can be set to deliver
a maximum current of 1.0 A, or use your power
source connected in series with a multimeter or
ammeter to monitor the output current. (Alternatively, to avoid possible damage to a sensitive
ammeter, you can measure the voltage drop across
a low-value series resistor, such as a 0.51 ohm, 1
watt resistor, and calculate the output current.) You
will also need to adjust and measure the output
voltage, so if your power supply does not have this
capability, you will need a multimeter or voltmeter.
(See Table 1 for specific suggestions for power
sources.)
Starting the motor
- The motor is not self-starting. Immediately after
you apply the power, start the motor manually by
grasping the black plastic bushing at the top of
the armature assembly between your thumb and
forefinger and spinning the armature.
source. This is impractical at frequencies
much above 30 Hz, and some students may
require assistance even a lower frequencies.
Maintenance and Storage
- A small box is provided for storing the parts of
the motor not installed on either the Variable
Gap Magnet or Coils and Cores Set.
- The commutators and brushes will experience
wear, oxidation, and pitting and will require attention from time to time. Rotate the armature
slowly by hand and monitor current flow or
sense the force developed to determine whether
proper contact is occurring between brushes and
commutator. To restore proper operation, clean
the contacts with emery paper or shift the
brushes somewhat to expose new surfaces.
- Careless installation of the armature onto the
shaft might bend the brushes. You can easily
bend them back into their original shape with
finger pressure.
➤ NOTE: If you are using a PASCO CI-
6502A Power Amplifier (for the CI-6500
Interface System), the distorted waveform light
will turn on during operation of the motor, but
no damage is being done to the Power Amplifier; you can ignore the light.
- With the Motor Accessory configured as either a
DC or universal motor, almost any attempt you
make at spinning the armature will result in successfully starting the motor; only the direction of
the spin is important.
- When configured in an AC synchronous mode,
the motor must be spun at a speed that approximately matches the frequency of the power
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Motor Accessory 012-06247A
Assembly
Motor Accessory onto the Variable Gap
Magnet
➀ Be sure you have the flat iron pole pieces placed on
the two neodymium magnets of the Variable Gap
Magnet. The larger threaded portion of the shaft
screws easily, without tools, into the threaded hole
in the magnet base. Insert the threaded end of the
shaft from above, screwing it in until 1 mm, or
slightly less, of the threaded portion remains above
the upper surface of the base.
➁ Turn the magnet over and screw the retaining nut
onto the smaller diameter threaded portion of the
dual slip-ring commutator
armature
brushes
shaft
(this end down for
AC motor)
split ring
commutator
(this end down for
DC motor)
brush holder
shaft that protrudes through the bottom of the magnet base. (Note that the retaining nut has a metric
thread, size M6-1.0.) Use firm finger pressure. If
this should prove inadequate, tighten the nut somewhat more with a wrench. If an appropriate wrench
is not at hand, use a heavy metal object to tighten
the nut by tapping the edge of the nut. Do not use
a pole piece of the magnet to tighten the nut because that might mar the finish of the pole piece.
Do not over tighten.
➂ Working from above, press the brush holder onto
the smooth, enlarged portion of the shaft. Apply
increasingly firm pressure equally to each side of
the brush holder while rotating the brush holder
back and forth. If this action loosens the retaining
nut, tighten it more tightly, as described in step 2.
Check to be sure the brush assembly is seated as far
down on the shaft as it will go.
➃ Gently lower the armature onto the shaft. To make
a DC motor, the split ring commutator should be
down; for an AC motor, the dual slip-ring commu-
tator should be down. Carefully rotate the armature back and forth to separate the brushes and allow the commutator to slip down between them. If
necessary, insert a pencil or similar object down
between the brushes. Use only the most delicate
force to avoid bending the brushes and necessitating adjustments or repairs.
flat pole pieces
neodymium
magnet
leave 1mm
exposed at
installation
magnet base
wrench/retaining
nut
Motor AccessoryVariable Gap Magnet Assembly
➄ Adjust the gap of the Variable Gap Magnet so there
is approximately 1 mm of clearance between the
pole pieces and the armature when it is rotated by
hand.
➅ Refer to the instructions included in experiments 1-
4 for details of the electrical connections.
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012-06247A Motor Accessory
Motor Accessory onto the Coils and Cores
Set
➀ Begin with the U-shaped core, with the coils and
any other parts removed. The smaller threaded
portion of the shaft screws easily into the threaded
hole in the core so the shaft is between the poles of
the core. Use the wrench provided to tighten the
shaft by gripping the flats on the larger threaded
portion. The small wrench limits the torque that
can be applied. If an ordinary wrench is used, be
careful not to over tighten.
ä
Note: Do not discard the small wrench; it
is essential as a retaining nut when the Motor
Accessory is used with the Variable Gap
Magnet.
➁ Working from above, press the brush holder
onto the smooth, enlarged portion of the shaft.
Apply increasingly firm pressure equally to each
side of the brush holder while rotating the brush
holder back and forth. If this action loosens the
shaft, tighten it as described in step 1. Check to
be sure the brush assembly is seated as far down
on the shaft as it will go. Orient the brush
holder perpendicular to the base of the Coils and
Cores apparatus.
➂ Place the two 400-turn coils from the Coils and
Cores Set onto the poles of the core.
➃ Gently lower the armature onto the shaft. The split
ring commutator should be down for use as a uni-
versal motor. Carefully rotate the armature back
and forth to separate the brushes and allow the
commutator to slip down between them. If necessary, insert a pencil or similar object between the
brushes to separate them. Use only the most delicate force to avoid bending the brushes and necessitating adjustment or repairs.
400
Motor AccessoryCoils and Cores Assembly
split ring commutator
U-shaped base
400
400-turn coil
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Motor Accessory 012-06247A
Suggested Uses
Operation as a DC motor
The Motor Accessory can be used with the Variable
Gap Magnet to demonstrate the operation of a DC
motor ( Experiment 1). Students can explore relationships between motor speed and voltage, as well as
between direction of armature rotation and polarity,
developing key concepts including: action of the split
ring commutator, dependence of speed on voltage,
dependence of direction of rotation on polarity, righthand rule, and direction of current flow from positive
to negative poles.
Action of AC and DC generators
Spinning the armature by hand while it is connected to
a sensitive DC meter or to the Signal Interface II
shows the action of an AC generator, as well as the
rectifying action of the commutator in a DC generator
(Experiment 2).
Operation of a synchronous AC motor
Operation as a universal motor
The Motor Accessory-Coils and Cores assembly
functions as a universal motor, operating on both AC
and DC power supplies (Experiment 4). Students can
explore the relationships of current direction and direction of the magnetic field, the effect of changes in
voltage and AC current frequency on motor speed, and
the effect of changes in DC voltage on motor speed.
Additional possibilities
The Motor AccessoryVariable Gap Magnet assembly
can be used to determine the speeds of maximum power
and maximum efficiency of a DC motor by varying the
load while simultaneously measuring the speed, torque,
and armature current. In this experiment, you can
measure the motors speed with a photogate or stroboscope.
The Motor AccessoryCoils and Cores assembly also
can be used to demonstrate series-wound, shunt-wound,
and hysteresis-synchronous motor setups.
Coupled with an AC signal supplied by the PASCO PI9587C Digital Function Generator/Amplifier or similar
function generator, the Motor Accessory-Variable Gap
Magnet assemblies will operate in sync with 15 and 30
Hz (and often wider range) signals (Experiment 3).
Students can explore the relationship between AC
voltage and motor speed, as well as between AC current
frequency and motor speed. They can conduct detailed
explorations of the precision of synchronism of AC
current and motor speed with a PASCO SF-9211
Digital Stroboscope or PASCO ME-9215A Digital
Photogate or by observing the stroboscopic effect of an
ordinary fluorescent lamp at selected motor speeds. As
a result, they develop key concepts, including the
independence of AC motor speed and voltage, dependence of AC motor speed on current frequency, and
action of a dual slip-ring commutator.
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012-06247A Motor Accessory
Experiment 1: Operation of the DC Motor
EQUIPMENT NEEDED:
• Motor Accessory • multimeter
• Variable Gap Magnet • patch cords
• low voltage DC power supply, limited to 1 A • small piece of masking tape
Purpose
The purpose of this experiment is to demonstrate the operation of the DC motor in terms of
basic concepts of electromagnetism.
Theory
Setup
The Variable Gap Magnet is a permanent magnet possessing a north pole and a south pole
that interact with the north and south poles of the armature (an electromagnet when connected to an electric current). Like poles repel, while unlike poles attract. The armature
rotates until its north pole is as close as possible to the south pole of the permanent magnet
(and also as far as possible from the north pole). Instead, if the rotational speed of the
armature matches the frequency of the alternating current, the direction of current in the
armature will reverse at that instant, so that the torque continues to act in the original direction.
A better explanation involves an understanding of fields. The variable gap magnet produces a magnetic field that passes through the gap between the pole pieces. When current
passes through the turns of the armature in the presence of the field, forces act to cause a
torque that rotates the armature. Inertia carries the armature past the position of no torque
to the point where the torque would force the armature back in the other direction. However, at that point the commutator reverses the direction of current in the armature so the
torque continues to act in the original direction.
➀ Be sure you have the flat iron pole pieces placed on the two neodymium magnets of the
Variable Gap Magnet. (The iron pole pieces spread the magnetic field over a wider
area.) Screw the larger threaded portion of the shaft into the threaded hole in the magnet
base. Insert the threaded end of the shaft from above, screwing it in until 1 mm, or
slightly less, of the threaded portion remains above the upper surface of the base.
➁ Turn the magnet over and screw the retaining nut onto the smaller diameter threaded
portion of the shaft that protrudes through the bottom of the magnet base. Use firm
finger pressure. Do not over tighten.
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Motor Accessory 012-06247A
➂ Working from above, press the brush
holder onto the smooth, enlarged portion
of the shaft. Apply increasingly firm
pressure equally to each side of the brush
holder while rotating the brush holder
back and forth. If this action loosens the
retaining nut, tighten it more tightly, as
described in step 2.
armature
brushes
dual slip-ring commutator
split ring
commutator
Check to be sure the brush assembly
is seated as far down on the shaft as it
will go.
➃ Gently lower the armature onto the shaft
with the split ring commutator down.
Carefully rotate the armature back and
forth to separate the brushes and allow
the commutator to slip down between
them. If necessary, insert a pencil or
similar object down between the brushes.
Use only the most delicate force to avoid
bending the brushes and necessitating
adjustments or repairs.
➄ Adjust the gap of the Variable Gap
Magnet so there is approximately 1 mm
of clearance between the flat pole pieces
and the armature when it is rotated by
hand.
➅ Connect the positive terminal of the DC
power supply to one end of the brush
holder with a red patch cord by plugging
the banana terminals into each.
brush holder
shaft
flat pole pieces
leave 1mm
exposed at
installation
magnet
base
wrench/retaining
nut
Figure 1. Installation of the Motor Accessory
onto the Variable Gap Magnet
➆ Connect the negative terminal of the DC
power supply to the other end of the
brush holder with a black patch cord.
Do not turn the power on.
wire connected to
the + terminal of the
power supply
Figure 2. Experimental Setup
METER
PUSH FOR
CURRENT
PASCO scientific
MODEL SF-9584 LOW VOLTAGE AC/DC POWER SUPPLY
0 - 24 VOLTS DC OUTPUT
DC VOLTAGE
8 AMP MAX
DC CURENT
8
ADJUST
12
10
8
14
6
16
18
4
ON
AC VOLTAGE ADJUST
ADJUST
2
24
2 - 24 VOLTS AC OUTPUT
6 AMP MAX
20
22
OFF
RESET
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