5 PIN RELAY

This is sometimes known as an ‘either/or’ relay because you can use either one circuit or the other. This type of relay is particularly useful for headlights. Pin number 87A feeds the dipped beam circuit. When the driver selects main beam the relay is energised so the moving contact moves to pin 87 and feeds the main beam circuit. So with the five pin relay you can have either dipped beam or main beam.

The basic relay works in three stages.

Stage 1:

When the switch (A) is closed, current flows through the winding around the soft iron core and down to earth at (B).This action magnetises the iron core.

Stage 2:

The magnetised iron core attracts the metal moving contact (C) which touches the fixed contact (D). Current can now flow from supply 2through the contacts and on to the load (E) e.g. a heated rear window.

Stage 3:

When the switch (A) is opened the current stops flowing around the iron core, so the magnetic field collapses. The moving contact is then pulled away from the fixed contact by the return spring (F). Current cannot now flow.

Switch on current to iron core.
Magnet closes relay contacts and current flows.
Switch off relay contacts opened by return spring.

If you look at the relay mounting plate in most vehicles (usually near the R-fuse carrier) you should see a few relays. The top of the range models usually have at least six. You need to know which relay pins are connected to the fixed and moving contacts in a relay. Each pin has a number or letter which tells you which contact the relay pins are connected to.

For a four pin relay the numbers and letters are.

86 or W2 Pin connected to supply side of the winding.
85 or W1 Pin connected to the earth side of the winding.
30 or C2 Pin connected to the moving contact.
87 or C1 Pin connected to the fixed contact.

With the basic four pin relay shown on page 90 the contacts are held open by a spring. A variation of this is when the contacts are normally closed. When a relay is not magnetised the contacts are said to be ‘at rest’. The contacts can be at rest in either an open or closed position.

Relays that have their contacts open when they are not magnetised are called normally open (N/O) relays.
Relays that have their contacts closed when they are not magnetised are called normally closed (N/C) relays.

For example a four pin relay that is normally closed can, be identified by the number 87A.

87 fixed contact on a normally open relay.
87A fixed contact on a normally closed relay.

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