Relay Circuit Assignment - Job #8
Here are the tasks to complete for this assignment. You may want to print
this page. Check off each task when done. Then move on to the next task.
Definitions Before You Begin
Be sure you have an understanding of these terms before beginning this exercise.
You may need to use a dictionary, a code book, a theory book, or even ask other
electricians you may know for help. This is part of the learning activity. Begin
now.
terminology
|
definition
|
forward
|
|
reverse
|
|
electrical interlock
|
|
mechanical interlock
|
|
4 pole double throw
|
|
Read this
As background, here are some details which will help you understand this
assignment. If you encounter words, terms, phrases or abbreviations which you do
not understand, then stop. Research the meaning before going on. This is very
important to your learning activity. The essence of any technical education
activity is comprehensive understanding of all topics which are encountered.
SOURCE
- Relay Basics:
 A relay is used to
isolate one electrical circuit from another. It allows a low
current control circuit to make or break an electrically
isolated high current circuit
path. One example where a relay is useful in car audio is in the
power antenna or remote output of a head unit. We already said that
the average remote lead can only handle about one half of an amp of
current. If a circuit with a large amount of current must be
controlled by the remote output lead of a head unit, a relay could
be used to buffer the remote output from the head unit. The basic
relay consists of a coil and a set of contacts. The most common
relay coil is a length of magnet wire wrapped around a metal core.
When voltage is applied to the coil, current passes through the wire
and creates a magnetic field. This magnetic field pulls the contacts
together and holds them there until the current flow in the coil has
stopped. The diagram below shows the parts of a simple relay.
- Relay Demo:
- Drag your mouse over the picture below. You'll see how the relay
closes to allow current to flow through the bottom lamp when the
coil is connected to the power source. You can see how current flows
through either set of contacts depending on the position of the
movable contact. If you have a slow connection, you may have to hold
your mouse over the image until it loads completely. Since this page
has a LOT of graphics, this will work best if you let the page load
completely before using this demo. Clicking on the picture will
bring the image to the top of the frame.
The table below shows just a fraction of the available
relay configurations.
|
 |
This is a Single Pole
Single Throw
relay. Current will only flow through the contacts when the relay coil
is energized. |
 |
This is a Single Pole
Double Throw
relay. Current will flow between the movable contact and one fixed
contact when the coil is DEenergized and between the movable contact and
the alternate fixed contact when the relay coil is energized. The most
commonly used relay in car audio, the Bosch relay, is a SPDT relay. |
 |
This is a Double Pole
Single Throw
relay. When the relay coil is energized, two separate and electrically
isolated sets of contacts are pulled down to make contact with their
stationary counterparts. There is no complete circuit path when the
relay is DEenergized. |
 |
This relay is a Double
Pole Double Throw
relay. It operates like the SPDT relay but has twice as many contacts.
There are two completely isolated sets of contacts. |
 |
Yep! You guessed it. This is a 4
Pole Double Throw
relay. It operates like the SPDT relay but it has 4 sets of isolated
contacts. |
- Relay Specifications:
- There are two specifications that you must consider when selecting
a relay for use in an automobile, the coil voltage and the current
carrying capability of contacts. The coil voltage for relays used in
automobiles is ~12 volts. This means that if you apply 12 volts to
the coil, it will pull in and stay there until the applied voltage
is removed from the coil. The current rating on relay contacts tells
how much current can be passed through the contacts without damage
to the contacts. Some relays have different current ratings for the
NC contacts (which are held together by spring tension) and the NO
contacts (which are held together by the electromagnet). If you need
to pass significant current through the NC contacts, you may want to
check the manufacturers specifications for the relay.
- The relay pictured above has a coil designed to accept 120 VAC at
50 to 60hz. If you look at the specifications on the relay cover
below, you will see that the coil was designed to operate on 120
volts A.C. There are relays designed for use with 5vdc, 12vdc,
12vac, 24vdc, 24vac. Make sure that you check the relay's
specifications when using a relay that you're not familiar with.
|
Go to the Diagram of this Job
Click HERE to go to the diagram, lecture, and picture for this exercise. Follow
the instructions found there. Then return to this page with your back button.
Connect the Components
Use the material list on the diagrams page to have ready all the components you
will need to complete this exercise. Connect all required components based on
the diagram.
Check your Connections
With the diagram as a guide, verify that all the connections have been made
properly.
Apply Power To Test
Wear safety glasses when testing this circuit. Locate the overcurrent protective
device for the circuit you will use. If possible, connect to a GFCI protected
circuit for the added safety. Be sure you have a full understanding of this
circuit before applying power. Then when you test the circuit, there should be
no problem with it working properly. Make corrections to the wiring as needed so
the circuit works properly. Memorize these connections.
Sketch the diagram from Memory
A sure way to determine if you have internalized this circuit is to draw a
sketch of the diagram from memory. You may choose to use a straight edge. But
that is not necessary. When you have completed the sketch, check it against the
diagram which is given for accuracy. Electricians must have the ability to
remember circuit connections without reference. Here is your chance to
demonstrate what you have learned. If you are unable to sketch the ladder
diagram from memory, refer back to the given ladder diagram. Then try again.
Repeat this activity until you feel confident that you can sketch this specific
diagram without reference.
Reconnect From Memory
Now on to the real test. Reconnect this diagramed circuit from memory. This will
ultimately tell you if you understand this circuit or not.
Review Before Answering Questions
Go back to review definitions, the diagram, the picture, your notes, your sketch
and any other details which will help you as you move on to the questions about
this diagram.
Answer the Questions
When you are satisfied that you can draw a sketch of the diagram, and wire it
all from memory, it is time to go on to answer questions about the diagram.
Click HERE to go to the questions.
Check Your Answers
When you have completed the questions, go on to check your answers. If you have
any which are different than the given answers, try to determine the reason. Go
back to the diagram. Research the question. Ask other electricians you may know.
But do all it takes to understand the correct answer to each question.
Click HERE to go to the answers.
Go On
When you can answer all questions without error, and strongly feel you
understand all answers, it is time to go on to the next assignment.
Click HERE to go on to the next assignment page.
If you would like to research any of these topics further, enter the search
term in this Google Search Box:
Use these Relay Circuit links to go to where you left off in
your online activities.
Job
|
Assignment
|
Diagram
|
Lecture
|
Picture
|
Questions
|
Answers
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
