011 918 0011 info@cw-services.co.za



A relay is an electronically operated switch that is remotely activated by an electromagnet which pulls a set of contacts to either make or break a circuit.

Electrical relays are commonly used for switching signals, radio frequencies, high current circuits when using a lower current circuit, and loads such as resistive, motor, lamp, inductive, and capacitive applications. This is helpful when an in-line switch or existing circuit does not have the capacity to handle the required current.

Functions of Relays:

  • Galvanic separation of the primary or actuating circuit and load circuits
  • Single-input/multiple-output capability
  • Separation of different load circuits for multi-pole relays
  • Separation of AC and DC circuits
  • Interface between electronic and power circuits
  • Multiple switching operations – time delay, signal condition, among others

What is a Relay used for:

We supply a wide range of relays including automotive high-voltage relays, automotive high-current relays, latching (bi-stable) relays and non-latching (monostable) relays, plug-in relays, high-frequency relays, reed relays, and solid state relays, also known as SSRs.

Our electromechanical relays are typically used for – among many other applications – electrical isolation, controlling power in manufacturing and transportation applications, and for switching smaller current values in a control circuit, such as in building automation technology and control panels. Relays serve as an amplifier.

Automotive Relays

High Voltage Relays

MIL-Aero Relays

Power Relays

Protective Relays

Relay Accessories, Sockets & Clips

Signal Relays

Time Delay Relays

How Relays Work:

Relays have the same subsystems and principles of operation regardless of whether these are electromechanical relays or electronic relays or designed to switch signal or high-power loads. Relays convert an electrical input signal on the primary side to an intermediate and non-electric physical signal. These devices also reconvert the non-electric physical signal to operate a switching element (secondary side) such as contacts which switch and conduct electrical current (i.e., output, load current). Relays use the non-electric signal between the primary and secondary side to provide the necessary galvanic separation between the input and output circuits. Relays enable a single output that can activate multiple circuits and functions, which helps increase cost savings because high current capacity switches cost more than lower current versions. Relays can also perform logic functions on certain inputs, such as latching an output on and off from a momentary input. When a switch cannot take a high current or is operated by electronic circuit, the relay can be operated by switch circuits. Arcing combined with contact bouncing is one of the parameters that limits inrush current. Care has to be taken during the design and testing phase of an application so that the peak inrush current will not exceed the relay specification, you need a high inrush relay when you need to address inrush currents that can be extremely high.

Understanding Signal Relays & Power Relays:

Signal relays switch signal, data, and voice up to approximately 2-amp resistive load. Typical applications include measurement systems, computer interfaces, and telecommunications equipment. Types of signal relays include yoke-type relays, reed relays, and solid state relays. Power relays can switch up to 600 volts and 100 amps. These relays offer high current switching that can overlap the switching range of contactors. There is a control scheme used in general purpose power relays that is known as pulse width modulation (PWM). The PWM scheme uses solid state control to operate and typically used to regulate the power requirements of the relay coil hold current. This, in turn, helps reduce heat dissipated by the relay coil. This scheme is generally employed for coil hold power efficiency and heat reduction of the relay coil and overall structure.

Electromagnetic Relays & Electronic Relays:

An electromagnetic relay can be classified according to the nature of the intermediate signal between the primary side and the switching element. A magnetic field generated by the input signal operates on the mechanical contacts. Examples include the standard yoke type relay and the reed relay. This standard yoke type of relay consists of a wire coil that is wrapped around a soft iron core, armature, and one or more sets of contacts. The wire coil generates an electromagnetic field when current is applied, which causes the armature to be activated. The armature is the moving part of the relay. It is hinged to the yoke and mechanically linked to the moving contacts, which opens and closes the contacts and has an attached spring that returns it to its original position. The armature is held in place by a spring, so when the relay is de-energized, there is an air gap in the magnetic circuit. While all versions offer the same basic operating concept, electrical relays are available in a variety of sizes and types using slightly different technologies. Electronic relays use electronic switches – such as transistors, triacs – as the main switching element. This allows the relay to control a much larger circuit. Other types of electronic relays – which transmit by other means, such as optically, frequency modulation, or capacitive effects – include optocouplers (on the primary side, an optical signal is transmitted by a light emitting diode, while a phototransistor acts as a receiver and controls the switching element), thermo-electric relays (input energy on primary side heats a bimetal part which actuates the contacts mechanically), and piezo relays (contacts are operated mechanically by the piezoelectric effect).

Understanding Non-Latching Relays & Latching Relays:

Relays can have several sets of contacts to change over multiple contacts. The contacts are operated by the armature movement and are normally open or normally closed depending on whether the relay is activated or opening a circuit. When a contact is open with the relay at rest, this is called Normally Open (NO), while if the contact is closed with the relay at rest the relay is Normally Closed (NC). NO relays are more common than NC relays. Non-latching (monostable) relays have only one stable position — OFF, or unenergized position. These will stay in this non-energize state, without receiving power. Most power relays are monostable relays with a neutral coil system. When power goes through the coil circuit, the relay switches to an energized position. An internal coil generates a magnetic force, which holds the energized position. When power is turned off, the relay returns to the unenergized position. Because of this, non-latching relays – also referred to as monostable relays – are useful in push-button applications like keyboards and micro-controller input button. While non-latching and latching relays are similar in design and function, the major difference between these two principles is that the latching relay will remain in the position it was last powered, while a non-latching relay returns to its normal position once coil power is removed from the coil. Latching (bistable) relays retain the switched position after interruption of the energizing current through the coil. To reset a latching relay, it is necessary to counter-energize the coil. Latching relays have two stable positions – ON and OFF – and maintain the last switching position. To change the state, an energy supply is needed. There are two advantages in using bistable relays: Zero power is consumed after switching, and the capacity of the relay to maintain its switched state even for prolonged periods. Also, since the relay coil is not energized, it will not generate heat, which means the relay will be cooler and have a wider current range. In latching relays, the memory effect of contacts means that the contacts do not change state even in the event of a power failure. Latching relays are used in many types of applications.

Other Types of Electrical Relays – ISO Relays & Slim Relays:

ISO relays are usually referred to as either mini ISO or micro ISO relays in the automotive area. These are usually also called plug-in relays and their faston arrangement follows the ISO specification. Mini ISO relays also differentiate between the mini ISO relay and the maxi ISO relay, sometimes called power mini relay. Slim relays are used for switching and control panels with about 6mm per channel. Highly compact and lightweight, these relays are useful when reducing space is a consideration. Slim relays are used in automation systems, DCS systems, machine manufacturers, PLC, and transportation systems.