Many types of automotive relays exist to meet the demands of various applications. Knowing the differences and understanding what to look for can be a huge help when deciding on the right relay for your build. While the list of automotive relays below is not exhaustive, it's a great start to seeing the options available.
Change Over RelaysThis is the most common type of relay. These automotive relays have the standard five pins and can be wired to be Normally Open (N.O.) using pins 30 & 87, Normally Closed (N.C.) using pins 30 & 87a, or wired as a Change Over (both N.O. & N.C.) using pin 30 & both pins 87 & 87a. When in use as a change over, the relay switches current from one circuit to another and back again, depending on the state of the coil (ON or OFF).
While a Change Over Relay could be wired to be Normally Open (N.O.), these Normally Open Relays only have four pins allowing them to only be wired one way - normally open.
Normally Open Relays
A Potted Relay is just like any other relay except the bottom is sealed with an epoxy to ensure a waterproof enclosure.
Flashers will have two or three pins as opposed to the four or five of a standard relay.
With a two pin flasher, the pins would be connected to power and the light circuit.
With a three pin flasher the additional pin would connect to an indicator light to let you know your flasher is on. While called a relay and usually found grouped in with the relays, not all flashers actually operate like a relay. Some act more like a circuit breaker.
Thermal (Standard) FlasherMany flasher relays are thermally controlled like a circuit breaker. The current flow through the coil of the flasher relay builds up heat. When enough heat is produced, it will cause the contacts inside the relay to deflect causing the contacts to open and stopping the current flow. Once enough heat has dissipated, the contacts deflect back to their original position and current flows once again. This constant make and break of the contacts produces the flash pattern of the turn signals. The number of lights connected to a thermal controlled flasher will affect its output performance.
Electro-Mechanical FlasherThese flashers use a circuit board containing a capacitor, a couple diodes and a coil to create the same flash pattern as a standard flasher. Electro-Mechanical Flashers are capable of handling higher loads with improved performance over thermal flashers. The number of lights connected to this type of flasher has less effect on the output.
LED FlashersLED Flashers are completely electronic in control and operation. They are controlled by a small Solid State Integrated Circuit (I.C.) board. The number of lights connected to an LED Flasher does not affect its output. Designed to work with the low current draw of LED lighting without causing issues.
Wig-Wag FlashersWig-Wag Flashers, also known as Alternating Flashers, use a solid state flash circuit to alternate between two separate lamp circuits.
Skirted Relays have an extended skirt around the bottom to seal around a socket to keep water and contaminants away from the contacts.
Time Delay Relays are adjustable in order to maintain the current flow through the contacts. Duration of current flow can be adjusted from as little as 2 seconds to as long as 3 minutes after power is switched OFF to the coil. The relay contains a solid state timing circuit with variable resistor that controls the time delay setting. One common use for these relays are for powering the vehicle parking lights for an extended time after you exit the vehicle to allow you to see around the vehicle.
Time Delay Relays
Dual Open Contact Relays
Dual Open Contact Relays have five pins like a Change Over Relay, but have a dual set of contacts instead of a single contact. This allows both pins 87 & 87a to be Normally Open (N.O.) inside the relay as opposed to 87a being Normally Closed (N.C.). These type of relays are common in European vehicles.
To learn more about relay functionality, read our blog post on how relays work.