Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [relay]

A relay is an electrically controlled switch. Electromechanical relays use an electromagnet to activate mechanical contacts, solid-state relays use semiconductor switches.

A latching relay stays in its current state when power is removed. A non-latching relay reverts to a known state when power is removed.

Relay contacts come in several varieties. The most common are:

  • A: normally open contact (NO)
  • B: normally closed contact (NC)
  • C: one normally-open and one normally-closed contact, both actuated by a single coil
  • X: normally open, double make
  • Y: normally closed, double break
  • Z: one X and one Y, both actuated by a single coil
3259 questions
46
votes
6 answers

Why is there a diode connected in parallel to a relay coil?

In most electrical circuits with a relay, a diode is connected in parallel to the coil of the relay. Why? Is it always a good practice?
Apostle
  • 571
  • 2
  • 5
  • 9
42
votes
6 answers

What are some ways to use relays more efficiently?

We often seem to use microcontrollers to control relays, and a 5 V microcontroller is often used with 12 V relays. A relay may need several times more power than the microcontroller. Not a problem if you can use an SSR, which you can drive at a few…
stevenvh
  • 145,832
  • 21
  • 457
  • 668
30
votes
6 answers

Why does a relay have a minimum applicable load?

I am trying to find relays for my application and I read a data sheet which looks fine but specifies Minimum applicable load: 10mV 10µA In my circuit, it is expected that the relay closes but no voltage and current is applied. You can think of it…
Thomas Weller
  • 1,049
  • 1
  • 12
  • 25
18
votes
2 answers

Why do I need space between two relays?

When I was reading the datasheet for these relays (http://www.mouser.com/ds/2/357/105A_117SIP_107DIP_171DIP-6475.pdf), it says to put 1/2" spacing between two adjacent relays. Why is this? As the relays are fully insulated, why would I have a…
dpdt
  • 1,717
  • 17
  • 27
13
votes
5 answers

Why are there three pins in this relay diagram?

I found this diagram on relays from A Guide To How A Relay Works. Why are both 2 and 3 needed? Wouldn't just one be sufficient? I am assuming that when the relay is powered, 1 gets magnetised and gets attracted to 4.
Manu Chadha
  • 413
  • 4
  • 13
13
votes
6 answers

Is there a kind of relay that consumes power only when switching?

The relay must stay in its state. When an electrical impulse is sent to it, it should switch its state and should maintain its status. So I am really curious about it. Is there such a thing for saving lots of power?
Barış Doğa Yavaş
  • 131
  • 1
  • 3
12
votes
5 answers

Are there "inverted relays"?

I'm a total beginner with circuitry, but for thinking through a project for I want to build as a hobby some day, I'd need an "inverted relay." A relay is, from my understanding this: I have a main powerline that I either want on or off, and I want…
JohnnySmithensen
  • 245
  • 2
  • 4
12
votes
3 answers

Is "humming" normal in an AC relay?

I have a 240V relay that uses a 120VAC coil. When I switch power to the coil, the relay makes a faint humming sound. It isn't very loud, and sounds like a transformer almost. A normal speaking voice or small fan in the room is enough to drown it…
A.R.
  • 558
  • 1
  • 7
  • 17
11
votes
3 answers

Why did relay run when I applied half the nominal coil voltage?

I'm using a RadioShack 12V DPDT relay, model 275-249. I applied 6 V across the coil and the switch closed. Why is this? I didn't have any resistors in series with the 6 V power supply (the only limiting resistance was that of the coil). I'm…
Mason
  • 543
  • 2
  • 8
  • 15
11
votes
1 answer

Preferred current flow in relay contacts?

Yet another relay question. In this document the moving and fixed part of a relay contact are named anode and cathode. This suggests that there's a preferred current flow through the contact in DC applications. Is this taken in consideration if both…
Federico Russo
  • 9,688
  • 17
  • 69
  • 119
10
votes
6 answers

What are the pins for in this Relay module?

I am trying to figure out how to use this relay module. There is no datasheet that I could find for the whole module, there however are for individual box. Here is the picture below, there are three jumper pins which read VCC, VCC, GND. And there…
fahadash
  • 205
  • 1
  • 3
  • 8
9
votes
4 answers

What are "pick-up", "dropout" and "rated" voltages in a Relay datasheet?

Given the picture below, what are these voltages? Okay, for the rated one, I "think" I know what it is in the practical sense but if someone would ask me: "what is it?" I would spend significant time to word it out. Thus, I am not sure what it…
Gold_Sky
  • 251
  • 1
  • 4
  • 9
8
votes
3 answers

Which relay - Mechanical or Solidstate?

Anyone familiar with relays mechanical or otherwise? I would like to be able to switch on/off up to 250W (120V) load using a microcontroller. Will be used to control lighting to an aquarium.
jdiaz
  • 1,943
  • 4
  • 21
  • 20
7
votes
5 answers

Can someone explain the different relay schematics contact types?

I'm looking at relays and there are multiple types of contacts forms, such as: A, B, C, X, Y, Z and much more. Searching around found different schematics for same form. Can someone explain them or show me a picture of the different contact forms?
Amir
  • 71
  • 1
  • 1
  • 3
7
votes
5 answers

Alternative to relay

Hi I want my circuit to be able to switch on and off several 230V AC circuits. I was wondering if relays are my only option. It starts to get a bit expensive if you need a few. Originally I was going to use a 5V dc relay to switch the devices on…
Ageis
  • 3,353
  • 14
  • 45
  • 67
1
2 3
…
22 23