What is a relay and how to use it?

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Atul0093 years ago

A relay is just a switch. How to use depends on type

most coomon SPDT has 5 pins to test it's pinout can vary but common on is like this

| 1 2 |

| 3 4 5 | where numbers are pins 3&5 are usally coil pins when energy is not supplied to them 4&2 are connect and as we push switch ennergy is given in coil pins then 4&1 gets connected and 4&2 gets disconnected.


try touching power supply of voltage written on it [not the 220v 50hz one its power of relay how much big thing it can operate( on and off)] try every possible combination and when you hear a tick they both are coil pins.

connected and not connected switch can be identified if you put a L.E.D. in one pin

other leg of led with battrie's terminal and latter terminal of battrie to remaining legs if led glows they are linke 4&2 in above diagram and if not they are like 4&1.

what about other types?

SPST is a bit easy it doen't have 2 , a normally connected one

never buyed a DPDT sorry :(

rickharris3 years ago

A relay is an electrically operated switch. It will have a stated coil voltage and may have several switched contacts.

Usually used to switch large currents or high voltage in a circuit -

associated words to look up:



Back EMF

snubber or flyback diode





A relay is basically a switch. Rather than having a toggle on it for a person to switch on and of it has a coil of wire in it. When the coil is energized by a power source it creates a magnetic field which turns the switch on. A quick internet search would have given you that.

I searched that but couldn't find a proper explaination on how to use it.And That's what I want.

iceng3 years ago

Here is a comparison of a mechanical relay

and any type of solid state transistor called a semiconductor.

  1. Relays can work with AC and DC, Semiconductors are DC only.
  2. Relays have zero closed resistance, Semiconductors have a forward voltage drop that wastes a little to lots of power.
  3. Relays have infinite open resistance, Semiconductors have a leakage that can affect attached electronics.
  4. Relays can operate at temperature extremes, Semiconductors are limited to 95°C and a little below zero.
  5. Semiconductors can operate at ( Megahertz ) speeds, Relays are much slower at 200 hertz.
  6. Semiconductors can be damaged and short .. due to voltage-peaking, secondary-breakdown over current, dv/dt and di/dt,.... Relays are primarily damaged by over-current.
  7. Relays have a very high isolation from the control coil, Semiconductors as a rule are not isolated from the base, gate or trigger
  8. Semiconductor switches almost never wear-out, Relays have a much shorter mechanical wear-out contact life.
  9. Semiconductors can amplify analog signals, Relays can only open and close.
  10. A semiconductor diode has almost no relay counterpart.

kjsrocks3 years ago

A relay is an electrically operated switch. Many relays use an electromagnet to mechanically operate a switch, but other operating principles are also used, such as solid-state relays. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits as amplifiers: they repeated the signal coming in from one circuit and re-transmitted it on another circuit. Relays were used extensively in telephone exchanges and early computers to perform logical operations.

A type of relay that can handle the high power required to directly control an electric motor or other loads is called a contactor. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device to perform switching. Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called "protective relays".

that was diretly off the wiki page