Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. Electromechanical Relays

Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc.

Electromechanical Relays


ObjectivesUpon completion of this tutorial, the student will be able to:

• Construct an experimental relay

• Describe how a relay works

• Observe basic relay functions


What is the purpose of a relay?

• A relay is an electromechanical device that uses small electrical currents and voltages to control larger electrical currents and voltages. Relays have unlimited possibilities, ranging from industrial applications to consumer electronics, such as microwave ovens and television sets.


• In a microwave oven, the push of a few tiny buttons on the keypad gives commands to a microcontroller, which can produce only very small output voltages. Those small voltages turn on a relay, which is capable of controlling the large voltages and currents required to produce the heating effect that takes place.

• In a television, the tiny impulses from the hand-held remote unit control a relay in the power supply.



• A relay is basically a switch that is controlled by an electromagnet.

• A relay is used when a large current needs to be turned on or off by a small current.

• Relays are used in many industrial applications as well as devices such as televisions, stereo systems etc.

Manufactured Relay

Homemade Relay



• A relay is basically a switch that is controlled by an electromagnet.

• A relay is used when a large current needs to be turned on or off by a small current.

• Relays are used in many industrial applications as well as devices such as televisions, stereo systems etc.

Electromagnet

Switching contacts

Switching contacts

Electromagnet

All electromechanical relays have three basic parts:1. Electromagnet – consists of an iron core wrapped with turns of insulated wire.2. Armature – this is the moving part of the relay.3. Switching contacts – at least one must be stationary and one fastened to the armature. This is known as a single-pole single-throw arrangement.

Armature

Armature

Note: In the manufactured relay, the switchingcontacts are insulated from the armature. Our experimental relay uses the metal armature and a 8d common nail as the switching contacts.


How to build a simple electromechanical relay

• Materials required:15’ #22 or #24 ga. Solid insulated hook-up wire.2 ea. 8d common nail1 ea. #8 flat washer1 small block of wood (approximately 2” x 3” x ½”)

Sheet metal or plumber’s strap

1 ea. ½ “ long self-tapping screw.

• Tools hammer or drill screwdriver metal shears wire stripper / cutter


• Begin by sliding the #8 washer on to the nail.

• Drill a hole for the nail, or use a hammer to drive the nail approximately ¾” – ½” from the edge of the block.

How to build a simple electromechanical relay


Part 1 - Winding the Electromagnet

• Slide the washer to the head of the nail. This washer will allow us to wrap 4 layers of wire.

• Allow at least 6” of wire under your left thumb. Begin by wrapping the wire in a clockwise direction.


• Continue winding the wire to the washer. Be sure to keep the turns close.

If you have never wound coils for electromagnets, try to be patient. Do not be in a hurry.



• When the windings reach the washer, continue winding clockwise on top of the previous layer. Wind toward the wood.



• After you wind the second layer down to the wood block, wind two more layers in the same manner as the first two for a total of 4 layers. Be sure to wind close and tight.



Completed electromagnetLeave approximately 6” of wire on both ends.

Twist wires together so that the windingswon’t unravel.


Part - 2- Armature and Switching Contact

• Drive another 8d common nail approximately 1 ½” from the center of the electromagnet nail.


Fabricating the Armature

• Cut a length of the plumber’s strap or other thin sheet metal to a length of 6.” If you are using sheet metal, be sure that it is a ferromagnetic material (iron based). Aluminum and copper will not work.


Fabricating the Armature

• Bend the strap 90° with pliers, as shown, so that it will be approximately ¼” above both nail heads. Use a small self tapping screw to attach the strap to the wood base. Drill a pilot hole if necessary.

Continued on next slide

3”


Adjusting the armature

The armature can be adjusted by trial and error bending.


Testing the electromagnet

When you touch the lead to the battery, the electromagnet should pull the armature down. The armature can be adjusted using trial and error bending.


Wire the lamp to the relay

Once the armature closes when the battery is connected you are ready for the last step. Connect the wire to the armature and the nail. Wire a low voltage lamp socket in series with a battery. When the electromagnetic relay closes, it completes the circuit allowing the lamp to light.


Build the Relay Circuit

Homosoteor Plywoodbase.

Switch

1.5 voltAA cell

Lamp

Strip and connectto armature screw

NegativebatteryConnection(black)

Strip end of wire. Wraparoundnail.

Strip and splice to + battery connection. (Red)

Schematic

Material List• lamp socket• 6 - 12 volt lamp • battery 6-9 or 12 volt• 24 or 22 gauge hookup wire.• AA cell • Plumber’s strap , switch• battery connector• self-tappingscrewsSolder or

tape wiresto cell.


Schematic Drawing of the Relay Circuit

Battery

This box is the schematicsymbol for the relay

Switching contact (nail)

Armature contact

Electromagnet

AA cell 1.5 v

Switch

The controlled device in this schematic is a 6 – 9 volt light bulb. You can use a DC motor or other device. The battery can also be changed to accommodate the particular device to be controlled. Experimentation is the key!

- +

Back to the finished

project

Documents

Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. Electromechanical Relays