Relays
A relay is an electromagnetically operated switch. Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts. The coil current can be ON or OFF so relays have two switch positions and they are double throw (changeover) switches.
A relay is an electromagnetically operated switch. Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts. The coil current can be ON or OFF so relays have two switch positions and they are double throw (changeover) switches.
Relays allow one circuit to switch a second circuit which can be completely separate from the first. For example a low voltage battery circuit can use a relay to switch a 230V AC volts circuit.
There is no electrical connection inside the relay between the two circuits, the link is magnetic and mechanical.
The coil of a relay passes a relatively large current, typically 30mA for a 12V relay, but it can be as much as 100mA for relays designed to operate from lower voltages.
· COM = Common, always connect to this, it is the moving part of the switch.
· NC = Normally Closed, COM is connected to this when the relay coil is OFF.
· NO = Normally Open, COM is connected to this when the relay coil is ON.
Reed Relays Reed relays consist of a coil surrounding a reed switch. Reed switches are normally operated with a magnet, but in a reed relay current flows through the coil to create a magnetic field and close the reed switch.
Reed relays generally have higher coil resistances than standard relays (1000 for example) and a wide range of supply voltages (9-20V for example). They are capable of switching much more rapidly than standard relays, up to several hundred times per second; but they can only switch low currents (500mA maximum for example).
The coil of a relay passes a relatively large current, typically 30mA for a 12V relay, but it can be as much as 100mA for relays designed to operate from lower voltages.
· COM = Common, always connect to this, it is the moving part of the switch.
· NC = Normally Closed, COM is connected to this when the relay coil is OFF.
· NO = Normally Open, COM is connected to this when the relay coil is ON.
Reed Relays Reed relays consist of a coil surrounding a reed switch. Reed switches are normally operated with a magnet, but in a reed relay current flows through the coil to create a magnetic field and close the reed switch.
Reed relays generally have higher coil resistances than standard relays (1000 for example) and a wide range of supply voltages (9-20V for example). They are capable of switching much more rapidly than standard relays, up to several hundred times per second; but they can only switch low currents (500mA maximum for example).
Advantages of relays:
· Relays can switch AC and DC.
· Relays can switch high voltages.
· Relays are a better choice for switching large currents (greater than 5A).
· Relays can switch many contacts at once.
Disadvantages of relays:
· Relays are bulky.
· Relays cannot switch rapidly (except reed relays).
. Relays use a lot of power due to the current flowing through their coil.
· Relays can switch AC and DC.
· Relays can switch high voltages.
· Relays are a better choice for switching large currents (greater than 5A).
· Relays can switch many contacts at once.
Disadvantages of relays:
· Relays are bulky.
· Relays cannot switch rapidly (except reed relays).
. Relays use a lot of power due to the current flowing through their coil.