the12volt.com spacer
the12volt.com spacer
the12volt.com - Free Technical Information for Mobile Electronics Installers, Enthusiasts, and Do-It-Yourselfers since 1999 Relay Diagrams - Quick Reference
the12volt.com spacer
the12volt.com - Free Technical Information for Mobile Electronics Installers
the12volt.com - Free Technical Information for Mobile Electronics Installers
BasicsCar AudioCar SecurityCruise ControlsDiodesDoor LocksOhm's LawPassive CrossoversRelaysResistorsSubwoofer Enclosures Search
the12volt.com - Free Technical Information for Mobile Electronics Installers
the12volt.com - Free Technical Information for Mobile Electronics Installers
the12volt.com - Free Technical Information for Mobile Electronics Installers
Application GuideCalculators, Charts, DiagramsDownloads/ManualsFind InstallersForumsGlossarySubwoofer WiringToolsVehicle Wiring Recent Topics
the12volt.com spacer
the12volt.com spacer
the12volt.com spacer
the12volt.com spacer
  the12volt.com spacer

the12volt.com spacer
the12volt.com spacer
the12volt.com spacer
the12volt.com spacer
Diodes
Glossary of Terms
Ohm's Law
Relays
Resistors
Tools and Equipment
Wire Sizes
Introduction
Parallel & Series Calcs
Passive Crossovers
Port Length Calculators
Subwoofer Box Calculators
Subwoofer Enclosure Types
Subwoofer Wiring Wizard
Thiele - Small Parameters
Miscellaneous
Relay Diagrams
Vehicle Wiring Database
Introduction
Alarm Accessories
Alarm Modules
Alarm Sensors
Basic Connections
Illuminated Entry
Light Flash
Power Door Locks
Starter Interrupts
Installation Pictorials
Relay Diagrams
Vehicle Wiring Database
Introduction
Electrical Connections
Mechanical Connections
Servo Settings
VSS and Tach Info
Vehicle Wiring Databse
All Forums
Buy & Sell Equipment
Car Audio
Car Audio Hot Topics
Car Security & Convenience
Car Security Hot Topics
Car Security Pictorials
Cellular & Communications
Cruise Controls
Employment
Fiberglass & Fabrication
General Discussion
Lights, Neon, LEDs, HIDs
Marine Electronics
Miscellaneous
Mobile Video & Navigation
Motorcycle Electronics
Music, Favorite Songs
Relays
Rides & Systems Gallery
Vehicle Information
Recent Forum Topics
Forum Help & How To
Forum & Site Notices
Books & DVDs
Calculators
Charts
Diagrams
Downloads - Manuals
Find an Installer
Forums - Q&A
Glossary of Terms
Insurance for Car Stereos
Links
Mobile Tech News
Relay Diagrams
The Application Guide
Vehicle Wiring Database
About the12volt
Support Us
the12volt.com spacer
the12volt.com spacer
the12volt.com spacer
the12volt.com spacer

 
the12volt.com spacer

SPDT and SPST Automotive Relays

SPDT Relays
If you are looking for relay diagrams, check out our relay diagrams quick reference.

SPDT Relay  : (Single Pole Double Throw Relay) an electromagnetic switch, consist of a coil (terminals 85 & 86), 1 common terminal (30), 1 normally closed terminal (87a), and one normally open terminal (87) (Figure 1).

When the coil of an SPDT relay (Figure 1) is at rest (not energized), the common terminal (30) and the normally closed terminal (87a) have continuity. When the coil is energized, the common terminal (30) and the normally open terminal (87) have continuity.

The diagram below center (Figure 2) shows an SPDT relay at rest, with the coil not energized. The diagram below right (Figure 3) shows the relay with the coil energized. As you can see, the coil is an electromagnet that causes the arm that is always connected to the common (30) to pivot when energized whereby contact is broken from the normally closed terminal (87a) and made with the normally open terminal (87).

When energizing the coil of a relay, polarity of the coil does not matter unless there is a diode across the coil. If a diode is not present, you may attach positive voltage to either terminal of the coil and negative voltage to the other, otherwise you must connect positive to the side of the coil that the cathode side (side with stripe) of the diode is connected and negative to side of the coil that the anode side of the diode is connected.

 
Single Pole Double Throw (SPDT) Relay Single Pole Double Throw (SPDT) Relay - Coil NOT Energized Single Pole Double Throw (SPDT) Relay - Coil Energized


SPST Relay  : (Single Pole Single Throw Relay) an electromagnetic switch, consist of a coil (terminals 85 & 86), 1 common terminal (30), and one normally open terminal (87). It does not have a normally closed terminal like the SPDT relay, but may be used in place of SPDT relays in all diagrams shown on this site where terminal 87a is not used.

Dual Make SPST Relay  : (Single Pole Single Throw Relay) an electromagnetic switch, consist of a coil (terminals 85 & 86), 1 common terminal (30), and two normally open terminals (87 and 87b). Dual make SPST relays (Figure 4) are used to power two circuits at the same time that are normally isolated from each other, such as parking lamp circuits on German automobiles.

The diagram below center (Figure 5) shows a dual make SPST relay at rest, with the coil not energized. The diagram below right (Figure 6) shows the relay with the coil energized. The coil is an electromagnet that causes the arms that are always connected to the common (30) to pivot when energized whereby contact is made with the normally open terminals (87 and 87b).
 
Dual Make Single Pole Single Throw (SPST) Relay Dual Make Single Pole Single Throw (SPST) Relay - Coil NOT Energized Dual Make Single Pole Single Throw (SPST) Relay - Coil Energized

Diodes are most often used across the coil to provide a path for current when the current path to the relay is interrupted (i.e. switched off, coil no longer energized). This allows the coil field to collapse without the voltage spike that would otherwise be generated. The diode protects switch or relay contacts and other circuits that may be sensitive to voltage spikes. (JimR, contributor, install bay member)

Why do I want to use a relay and do I really need to? Anytime you want to switch a device which draws more current than is provided by an output of a switch or component you'll need to use a relay. The coil of an SPDT or an SPST relay that we most commonly use draws very little current (less than 200 milliamps) and the amount of current that you can pass through a relay's common, normally closed, and normally open contacts will handle up to 30 or 40 amps. This allows you to switch devices such as headlights, parking lights, horns, etc., with low amperage outputs such as those found on keyless entry and alarm systems, and other components. In some cases you may need to switch multiple things at the same time using one output. A single output connected to multiple relays will allow you to open continuity and/or close continuity simultaneously on multiple wires.

There are far too many applications to list that require the use of a relay, but we do show many of the most popular applications in the pages that follow and many more in our Relay Diagrams - Quick Reference application. If you are still unclear about what a relay does or if you should use one after you browse through the rest of this section, please post a question in the12volt's install bay. (We recommend Tyco (formerly Bosch) or Potter & Brumfield relays for all of the SPDT and SPST relay applications shown on this site.)


Relays and Relay Diagrams:
Converting Polarity
Starter Interrupts
Door Locks
Illuminated Entry & Light Flash
Special Applications
Relay Diagrams - Quick Reference
Relay Forum
Mobile Electronics Basics:
Diodes
Ohm's Law
Relays
Resistors
Tools and Equipment

Car Security:
Basic Connections
Car Alarm Modules
Car Alarm Sensors / Triggers
Light Flash / Illuminated Entry
Starter Interrupts
Accessories & Add-ons
 





space
the12volt.com spacer
google plus
Search the12volt.com
Custom Search
Follow the12volt.com: Follow the12volt.com on Facebook
Share, print & email this page:
Thursday, December 18, 2014 Copyright © 1999-2014 the12volt.com Donate to the12volt.com Privacy Policy Advertising
the12volt.com spacer
the12volt.com spacer
the12volt.com spacer
BasicsCar AudioCar SecurityCruise ControlsDiodesDoor LocksOhm's LawPassive CrossoversRelaysResistorsSubwoofer Enclosures Search
the12volt.com - Free Technical Information for Mobile Electronics Installers
the12volt.com - Free Technical Information for Mobile Electronics Installers
the12volt.com - Free Technical Information for Mobile Electronics Installers
Application GuideCalculators, Charts, DiagramsDownloads/ManualsFind InstallersForumsGlossarySubwoofer WiringToolsVehicle Wiring Recent Topics
the12volt.com spacer
the12volt.com spacer
the12volt.com spacer
the12volt.com - Free Technical Information for Mobile Electronics Installers, Enthusiasts, and Do-It-Yourselfers since 1999 Donate to the12volt.com
the12volt.com spacer
the12volt.com spacer