Seamless power flow with our electromechanical power relays
Power relays open or close a circuit by using an electromagnetic coil for seamless power flow. These cost-efficient relays are manufactured with an armature, spring, and one or several contacts. If the relay is meant to be normally open (NO), when power is applied the electromagnet attracts the armature. It is pulled in the coil’s direction until it reaches a contact, resulting in closing the circuit. Similarly, if the relay is meant to be normally closed (NC), the electromagnetic coil pulls the armature away from the contact, resulting in opening the circuit.
Our relays can be used anywhere in the intelligent building system — in elevators and escalators, control panels, motion control systems, lighting, building systems, and an array of safety-critical applications to mention just a few. In this Application Guide, you can find our relays products suitable for use in building equipment including HVAC, lighting and solar applications. Here you can find cost-effective, reliable solutions designed to withstand extreme shock, vibration, temperature, and altitude, from our recognized brands: AGASTAT, AXICOM, Potter and Brumfield, PRODUCTS UNLIMITED, SCHRACK, OEG as well as TE.
What is a Power Relay?
Power relays are categorized by mechanical features – miniature, PCB, industrial, and more. While miniature power relays are small this term does not always indicate absolute size, PCB power relays are designed to mount onto printed circuit boards (PCBs). Industrial relays are typically used in switching cabinets by control panel builders. Industrial relays are engineered to meet industry expectations such as Underwriters Laboratory (UL).
The basic design of electromechanical power relays is the same, regardless of whether it is a miniature PCB relay or an industrial power relay. Power relays have three subsystems: contact system, magnetic system, and mechanical components.
The primary components in a power relay include – on the contact system, or secondary side – fixed contacts, moving contacts (moved by the magnetic system – the motor – to switch the load circuit), and contact springs (holding the contacts but flexible enough to all the contacts to move).
The magnetic system includes the coil (generates the necessary magnetic field to actuate the armature and contacts), the core, the yoke (establishes the magnetic circuit), the armature (the moving part that closes and opens the magnetic circuit and acts – via a comb or actuator – on the moving relay contacts), and the return spring (establishes the defined position of the magnetic and contact system in case the coil is not energized).
The mechanical components include the case, base, insulation (separates the primary circuit from the secondary side and provides required insulation), actuator (can translate motion of magnetic system to the moving contacts), pins or terminals (connects the contact system and the load), and mounting devices.
Most power relays are monostable (non-latching) relays with a neutral coil system, and only one stable position. These will stay in this non-energize state, without receiving power.
Incandescent lamps, inductive loads like motors and solenoids, capacitive loads like electronic ballasts and switching power supplies, etc. can exhibit very high initial surge currents upon energizing. This can be up to 10X the steady state current or more and is especially troublesome should the contact closure randomly occur near the peak of the voltage sine-wave. Welding of contacts due to such excessive surge current is often the result. Relays for such applications usually need to be oversized or specially designed to handle the high inrush current relative to the relatively modest steady state current. This usually results in extra control cost and increased space usage. The application notes looks at how synchronizing contact can make and break to the load voltage and current can yield marked improvement in performance when properly implemented.
Power relays are used in automotive, control, power, safety, and signal systems. In building systems, such as elevators and escalators, power PCB relays are designed for PCB mounting primarily in elevator control sub systems, door control, and illumination. In HVAC, power PCB relays are used in thermostats, electric boilers (to switch on heating time), general pumps and fan control to name a few. In lighting systems, inrush power relays are especially suitable for electronic ballast and LED lighting. Other applications include movement detectors, remote controls and bus system actuators.
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