Mechanical and Electronic Relays

Relays, one of the oldest and most common elements used in electronic circuits, are the electromechanical materials that allow switching between low voltage and high voltage. When the coil located on the low voltage side is energized, the mechanical contact on the high voltage side moves and switches the high voltage side to transmission. They can also be used to switch high currents at the same level of voltage. Relays can also be used to isolate two circuits from each other. Relays used for high power and current switching, usually the coil of which operates with a mains voltage of 220V, are called “contactors”. Relays were also used in automation circuits when electronic PLC systems were not yet widespread.

Although the working principle of the relays is simple, they have quite a lot of varieties according to the field of application. They can be divided into 2 as “mechanical” and “electronic”. Mechanical relays can lose their properties when worn out over time as they have moving parts, while electronic relays are made of semiconductor materials and their service life is quite longer than that of mechanical relays. Electronic relay is especially advantageous in applications where very fast switching is performed or where a long service life is required. Mechanical relays, on the other hand, can provide higher current and voltage values than electronic relays. The contacts of the relays can be in different combinations. N.0: (Normally Open) The contact is open when the relay coil is not energized. N.C: (Normally Close) Indicates that the contact is closed when the relay coil is not energized. Relay contact combinations are expressed in 3 different ways as 1 FORM A, 1 FORM B and 1 FORM C.

“The type of load to be used should be taken into account when selecting a relay.”

1 FORM A:

It is a 2-pin contact, and the section between 2 pins is an “open circuit” when the relay coil is not energized. When the coil is energized, it switches to the short circuit position.

1 FORM B:

It is a 2-pin contact, and the section between 2 pins is a “short circuit” when the relay coil is not energized. When the coil is energized, it switches to the open circuit position.

1 FORM C:

It is a 3-pin contact, and when the relay coil is not energized there is a short circuit between COM (common pin) and N.C. pin, while the N.O. pin is in open circuit state. When the relay coil is energized, there is a short circuit between the COM and N.O. pins and an open circuit between the N.C. pins. When the relay is energized, the contacts change their positions and must remain under constant energy in order to maintain this position. This poses a problem in designs where current consumption is important. Latch-type relays have been developed to prevent this problem. To change the contact position of latch-type relays, it is sufficient to only give a trigger and there is no need for continuous current consumption. There are 2 types of latch-relays available as single-coil and double-coil. The latch relay, which is a single coil type, has a 2-pin coil and it is necessary to change the poles of the voltage given to the coil to change the contact. For instance, if the contact is pulling in the 1+ 2 – direction (SET position), it will release the contact in the 1- 2+ direction (RESET position). The latch-relay with 2 coils, on the other hand, has 3 pins. The middle pin is the common pin, and one of the other pins pulls the contact (SET position) while the other releases the contact (RESET position).

The type of load to be used should be taken into account when selecting a relay. There are 3 different load types available: Resistive, inductive and capacitive. Relay selection is important particularly for capacitive loads. When there is a high capacitive load in the circuit, an inrush current much higher than the nominal current will occur when the initial power is applied. If the relay used is not resistant to inrush current, the relay contacts may stick to each other. The materials used in the relay contacts determine this property. Relay manufacturers produce special relays for such applications. Ozdisan Elektronik offers its customers both mechanical and electronic relay solutions under Panasonic brand, which has proven its quality for years.