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What role do relay boxes play in a car?

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What is a relay?

A relay is an electrically operated switch. It consists of a set of input terminals for a single or multiple control signals, and a set of operating contact terminals. The switch may have any number of contacts in multiple contact forms, such as make contacts, break contacts or combinations thereof.

  • SPST-NO (Single-Pole Single-Throw, Normally-Open) relays have single make contact or make contact. These have two terminals which can be connected or disconnected. Including two for the coil, such a relay has four terminals in total.
  • SPST-NC (Single-Pole Single-Throw, Normally-Closed) relays have a single break contact or break contact. As with an SPST-NO relay, such a relay has four terminals in total.
  • SPDT (Single-Pole Double-Throw) relays have a single set of change over or transfer contacts, break before make or transfer contacts. That is, a common terminal connects to either of two others, never connecting to both at the same time. Including two for the coil, such a relay has a total of five terminals.
  • DPST – Double-Pole Single-Throw relays are equivalent to a pair of SPST switches or relays actuated by a single coil. Including two for the coil, such a relay has a total of six terminals. The poles may make contacts or break contacts (or one of each; the designations NO and NC should be used to resolve the ambiguity).
  • DPDT – Double-Pole Double-Throw relays have two sets of change over or transfer contacts. These are equivalent to two SPDT switches or relays actuated by a single coil. Such a relay has eight terminals, including the coil

Where relays are used?

Relays are used wherever it is necessary to control a high power or high voltage circuit with a low power circuit, especially when galvanic isolation is desirable.

  • 85 = relay coil –
  • 86 = relay coil +
  • 87 = common contact
  • 87a = normally closed contact
  • 87b = normally open contact

relay wiring diagram

Why relays are used?

Relays are used where it is necessary to control a circuit by an independent low-power signal, or where several circuits must be controlled by one signal. Examples include headlamps, rear-window defoggers, fuel pumps, A/C compressor clutches, cooling fans, heaters, fan blowers, abs systems, ignition circuits, power windows, seats, and horns.

How do relays work?

The electromagnet starts energizing when the current flows through the control coil and then intensifies the magnetic field. The electromagnet becomes connected to the power source through the contacts to the load and a control switch. The upper contact arm becomes attracted to the lower fixed arm and then closes the contacts that result in a short circuit. The contact then moves in the opposite direction and creates an open circuit once the relay has been de-energized.

The movable armature will return to its initial position when the coil current is off. The force that causes its movement will be almost the same as the half strength of the magnetic force. Spring and gravity provide this force.

Relay Design

What is the purpose of the fuse box and relay box in the car?

Because the relays are changed and closed frequently, they need their own fuses to protect them. In practical application, it is placed in the same position as the fuse. That’s why the fuse and relay are sometimes in the same box. Fuses are used in automobiles to limit current flow and prevent fires. A relay is a switching device that uses a small current to control a much larger current in a second circuit.

In addition, the relay box can keep all fuses and relays in an easy-to-find and diagnose place for quick repair and replacement. Such as Daier’s relay boxes: RB-R6F6, RB-R6F6-W1, RB-R6F6-W1-B, RB-R4F12-W1, RB-R6F11, RB-R6F11-W1, RB-R10F15 and RB-R4F15-W1.

RB-R6F11 Relay Socket

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