Electromechanical Relays Vex 1 0 2005 Carnegie Mellon

Electromechanical Relays Vex 1. 0 © 2005 Carnegie Mellon Robotics Academy Inc.

Objectives Upon completion of this tutorial, the student will be able to: • Construct an experimental relay • Describe how a relay works • Observe basic relay functions Vex 1. 0 © 2005 Carnegie Mellon Robotics Academy Inc.

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. Vex 1. 0 © 2005 Carnegie Mellon Robotics Academy Inc.

• 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. Vex 1. 0 © 2005 Carnegie Mellon Robotics Academy Inc.

What is the purpose of a Homemade Relay relay? • A relay is basically a switch that is controlled by an electromagnet. Manufactured Relay • 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. Vex 1. 0 © 2005 Carnegie Mellon Robotics Academy Inc.

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. What is the purpose of a relay? • Armature A relay is basically a switch that is Switching contacts controlled by an electromagnet. • A relay is used when a large current Armature Switching needs to be turned on or off by a small contacts current. • Relays are used in many industrial applications as well as devices such as Electromagnet televisions, stereo systems etc. Note: In the manufactured relay, the switching Electromagnet contacts are insulated from the armature. Our experimental relay uses the metal armature and a 8 d common nail as the switching contacts. Vex 1. 0 © 2005 Carnegie Mellon Robotics Academy Inc.

How to build a simple electromechanical relay • Materials required: 15’ #22 or #24 ga. Solid insulated hook-up wire. 2 ea. 8 d common nail 1 ea. #8 flat washer 1 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 Vex 1. 0 © 2005 Carnegie Mellon Robotics Academy Inc.

How to build a simple electromechanical relay • 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. Vex 1. 0 © 2005 Carnegie Mellon Robotics Academy Inc.

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. Vex 1. 0 © 2005 Carnegie Mellon Robotics Academy Inc.

Part 1 - Winding the Electromagnet • 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. Vex 1. 0 © 2005 Carnegie Mellon Robotics Academy Inc.

Part 1 - Winding the Electromagnet • When the windings reach the washer, continue winding clockwise on top of the previous layer. Wind toward the wood. Vex 1. 0 © 2005 Carnegie Mellon Robotics Academy Inc.

Part 1 - Winding the Electromagnet • 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. Vex 1. 0 © 2005 Carnegie Mellon Robotics Academy Inc.

Completed electromagnet Leave approximately 6” of wire on both ends. Twist wires together so that the windings won’t unravel. Vex 1. 0 © 2005 Carnegie Mellon Robotics Academy Inc.

Part - 2 - Armature and Switching Contact • Drive another 8 d common nail approximately 1 ½” from the center of the electromagnet nail. Vex 1. 0 © 2005 Carnegie Mellon Robotics Academy Inc.

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. Vex 1. 0 © 2005 Carnegie Mellon Robotics Academy Inc.

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. 3” Continued on next slide Vex 1. 0 © 2005 Carnegie Mellon Robotics Academy Inc.

Adjusting the armature The armature can be adjusted by trial and error bending. Vex 1. 0 © 2005 Carnegie Mellon Robotics Academy Inc.

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. Vex 1. 0 © 2005 Carnegie Mellon Robotics Academy Inc.

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. Vex 1. 0 © 2005 Carnegie Mellon Robotics Academy Inc.

Build the Relay Circuit Material List Strip and connect to armature screw Lamp Negative battery Connection (black) Schematic Strip end of wire. Wrap around nail. Strip and splice to + battery connection. (Red) Switch 1. 5 volt AA cell Solder or tape wires to cell. • 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-tapping screws Homosote or Plywood base. Vex 1. 0 © 2005 Carnegie Mellon Robotics Academy Inc.

Schematic Drawing of the Relay Circuit Switching contact (nail) Armature contact 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! This box is the schematic symbol for the relay Switch Electromagnet - + Battery AA cell 1. 5 v Vex 1. 0 © 2005 Carnegie Mellon Robotics Academy Inc.