Electromechanical Relay

All about working of electromechanical relay and their uses...

1. Electromechanical Relays
EMT Application
GROUP MEMBERS
M.SALMAN SAMI
ASAD-UR-REHMAN
NOUMAN AKRAM
DANISH ALI

2. Outline
•Why Electromechanical Relays?
•Common Applications of Electromechanical
Relays
•The Principle Behind Electromechanical Relays
•What’s Inside an Electromechanical Relay
•Typical Sample Application
•Electromechanical Relay Advantages and
Limitations
•Important Specifications of
Electromechanical Relays
•Conclusion
Thursday, April 16, 2015

3. Why Electromechanical
Relays?
•Separation of AC and DC circuits
•Interface between electronic control
circuits and power circuits
Thursday, April 16, 2015

4. The Principle Behind
Electromechanical Relays
A relay is similar to a switch, it is either open or
closed. When the switch is open no current passes
through the relay, the circuit is open, and the load
that is connected to the relay receives no power.
When a relay is closed, the circuit is completed and
current passes through the relay and delivers power
to the load
To open and close a relay an electromagnet is
used. When the coil controlling the electromagnet is
given a voltage, the electromagnet causes the
contacts in the relay to connect and transfer current
through the relay.
Thursday, April 16, 2015

5. Electromechanical Relays:
What’s Inside
This diagram shows the
basic parts of an
electromechanical relay: a
spring, moveable armature,
electromagnet, moveable
contact, and stationary
contact. The spring keeps
the two contacts separated
until the electromagnet is
energized, pulling the two
contacts together.
Moveable Armature
Moveable Contact
ElectromagnetSpring
Stationary Contact
Thursday, April 16, 2015

6. Wiring Up an Electromechanical
Relay
Spring
To Control Circuit
Moveable Armature
Moveable Contact
Load
Power Supply
Electromagnet
This diagram shows how to
wire an electromechanical
relay. When the control
circuit turns the
electromagnet on, the
moveable armature is
drawn towards the
electromagnet and
connects the moveable
contact and the stationary
contact. This completes
the circuit and delivers
power to the load.
Stationary Contact
Thursday, April 16, 2015

7. Typical Sample Application
Suppose, there is a need to control a solenoid valve
for a water drain application. Control is to be
accomplished with a microcontroller. The solenoid
valve requires 120 VAC to open. Assuming that a 120
VAC power supply is available, how can control of the
solenoid valve be accomplished using a microcontroller
that can only supply.
This problem is easily solved using a relay. There are
many relays that are turned on and off with a 5 VDC
coil. The relay provides the interface between the
microcontroller and the 120 VAC power supply that is
needed to open and close the valve.
Thursday, April 16, 2015

8. Typical Sample Application
120 VAC
Ground
To Microcontroller
Solenoid Valve
Relay
Coil
Circuit for Control of a 120 VAC Solenoid Valve
Thursday, April 16, 2015

9. Electromechanical Relay
Advantages
•Contacts can switch AC or DC
•Low initial cost
•Very low contact voltage drop, thus no heat
sink is required
•High resistance to voltage transients
•No Off-State leakage current through open
contacts
Thursday, April 16, 2015

10. Electromechanical Relay
Limitations
•The contacts wear and thus have limited life
depending on loads
•Short contact life when used for rapid
switching applications or high loads
•Poor performance when switching high inrush
currents
•Package Size
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11. Important Specifications of
Electromechanical Relays
•Coil Voltage – Voltage required for switching
•Contact Rating – How much current the relay
can handle
•Normally Open (NO) or Normally Closed (NC)
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12. Common Applications of
Electromechanical Relays
•Solenoid Activation Control
•Many Automotive Applications (Electric Fuel
Pump)
•Motor Control
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13. Conclusion
Electromechanical relays are an excellent
solution to separate electronic control
circuitry and power circuitry.
Electromechanical relays are not the best
choice in high frequency switching
applications and do have a limited life due to
wear on the contacts inside the relay. When
used in the a proper application, the
electromechanical relay provides safe and
reliable integration between power circuits
and control circuits.
Thursday, April 16, 2015

14. Reference List
•http://www.rowand.net/Shop/Tech/AllAboutRelays.htm
•http://relays.tycoelectronics.com/schrack/pdf/C0_v4bg_2.pdf
•http://www.cutler-
hammer.eaton.com/unsecure/html/101basics/Module18/Output/Electromechanic
alRelays.html
•http://www.msdignition.com/pdf/8961_8960_msd_relays.pdf
•http://zone.ni.com/devzone/conceptd.nsf/webmain/7C83114818EAA85786256D
D400569EB7?opendocument
•http://www.ibiblio.org/obp/electricCircuits/Digital/DIGI_5.html
Thursday, April 16, 2015

15. Links To Explore Further
•http://www.allegromicro.com/techpub2/phoenix/relay5.htm -
Solid State Relays
•http://www.ssousa.com/appnote040.asp - Electromechanical
Relays vs. Solid State Relays
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16. THANK YOU....!
Thursday, April 16, 2015