Relay wiring to control AC Load

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I am being confused on basics concept of realy wiring to control AC load.

 

Should the LIVE input be connected to NO terminal or COM terminal? 

 

https://www.electronicscomp.com/1-channel-5v-relay-module-without-optocoupler?gclid=Cj0KCQjwpImTBhCmARIsAKr58cxrbE_RsN0dWwBKaIm2kzGwn7nKBH6ALejWGx97g3AWmUm6MizO4M8aAj0MEALw_wcB

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Last Edited: Sat. Apr 23, 2022 - 11:19 AM
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The "Mains" (output) side of the relay has three contacts:

NO

NC

Comm

 

The Comm is the Common, or common to both NO and NC pins.

One side of the Mains power will connect to this terminal.

 

The NO is Normally Open, (Off, Disconnected), when the relay is not energized.

The NC is Normally Closed, (On, Connected), when the relay is not energized.

 

The other side of the Mains power will be connected to one or the other of the NO and NC pins, depending upon how you want the Relay and the power to work.

 

If you connect your Mains device to the Comm and the NO, then the device will be off until the relay is energized.

 

As Mains power switching relays are typically placed on the HOT / Live / 120/240 side of the power connections, BOTH the NO (or NC), and the Comm pins/terminals will be at 120/240 V potential when the relay is energized.

It therefore doesn't really matter whether the Hot / Live wire goes to the Comm or to the NO (or NC) pin/terminal.

 

If the relay was, for some reason, to be placed on the "low side", i.e. the Neutral / Ground side of the device, then which wire goes to which terminal can impact the PCB routing and where the board is always hot vs where it is only hot during a fault condition.

 

So, bottom line, it won't matter which way you wire this up.

 

JC

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If you want to use both NO and NC loads, then the line must connect to the COM, otherwise won't matter

Make sure to maintain physical isolation (creepage and clearance) between the coil traces and the power traces. 

 

I just saw a board with an optoisloator where they ran some traces between the sets of pins---ruining the isolation gap.  Some layout!

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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If I don't supply power to the input terminal of the relay then I would expect the Red light to always be on and Green light to always off. 

 

If I supply power to the input terminal of the relay then I would expect the Red light to always be off and Green light to always on. 

 

Take a look at diagram

Attachment(s): 

Last Edited: Sat. Apr 23, 2022 - 04:36 AM
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How you will connect both Red and Green light, connecting in serial is not that easy - depends on load current.

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grohote wrote:

How you will connect both Red and Green light, connecting in serial is not that easy - depends on load current.

If there is a DC load instead of a light, is the relay connection correct?

 

 

This reply has been marked as the solution. 
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muke12 wrote:

If I don't supply power to the input terminal of the relay then I would expect the Red light to always be on and Green light to always off. 

 

If I supply power to the input terminal of the relay then I would expect the Red light to always be off and Green light to always on. 

 

Take a look at diagram

 

You are correct. In your picture the NC (Normally Closed) terminal will be connected to the COM (Common) terminal when the coil is NOT energized, thus feeding positive to your red light. The NO (Normally Open) terminal will not be connected to the COM terminal when the coil is NOT energized, therefore no positive connection to the green light will exist.

 

When the coil IS energized, the NC terminal will go open disconnecting from the COM, and the NO terminal will close contact with the COM instead, removing the positive connection to the red light and instead feeding it to the green light.

 

Just heed what Grohote said, if those are LED's you will need current regulating resistors.

 

SAFETY NOTICE: I would NOT recommend using one set of relay terminals on a DPDT relay for 24V and the other for mains. Funky things will most likely happen at some point for a beginner! (Not a good idea for anybody to do this, just a beginner would be more prone to seeing fireworks than a seasoned engineer)

Wayne

East London
South Africa

 

  • No, I am not an Electronics Engineer, just a 54 year old hobbyist/enthusiast
  • Yes, I am using Proteus to learn more about circuit design and electronics
  • No, I do not own a licensed copy of Proteus, I am evaluating it legitimately
  • No, I do not believe in software or intellectual property piracy or theft
Last Edited: Sat. Apr 23, 2022 - 06:41 AM
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muke12 wrote:
DC load

 

Where is the DC load, it is the first thing to put on picture: voltage source and load, led light is not important.

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SAFETY NOTICE: I would NOT recommend using one set of relay terminals on a DPDT relay for 24V and the other for mains. 

To be clear, this is general advice and not your cicuit (which is using a SPDT relay). 

 

How you will connect both Red and Green light, connecting in serial is not that easy

He didn't mention anything like that....only to turn on red or green, not both.  One of the two will be on at any moment.

 

I am being confused on basics concept of realy wiring to control AC load.

What AC load??? You don't have any, just 2 DC loads.

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Sat. Apr 23, 2022 - 07:31 AM
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WayneZA wrote:
SAFETY NOTICE: I would NOT recommend using one set of relay terminals on a   for 24V and the other for mains. Funky things will most likely happen at some point for a beginner! (Not a good idea for anybody to do this, just a beginner would be more prone to seeing fireworks than a seasoned engineer)
Seems that OP need DPDT relay switch.Added the other lamp in series.

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Jeckson, please! Think before of posting... It is a schematic for TWO-SWITCHES-ONE-LAMP and not a relay.

 

Last Edited: Sat. Apr 23, 2022 - 10:50 AM
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Replace the switch’s with relay.

www.tokopedia.com/madagang .Buy and Donated cheap electronics and manuscripts.

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Do it, continue with nonsense.

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I think your core question is already answered. But I think a side note can be helpful regarding safety: Make sure that the relay is rated for the AC voltage and power you want to switch and preferably has a national certificate (if so, sign is printed on the relay).  But there are many more security rules to be considered.

 

My advice is therefore to have your device checked by a grid authorised/educated person BEFORE you connect it to the grid. 

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Ignore this #10, it means nothing for your relay.   It shows one form of a 3-way switch, not sure why it was posted.

 

 

 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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avrcandies wrote:
To be clear, this is general advice and not your cicuit (which is using a SPDT relay).

 

You are quite right, I just thought based on the initial mains question then the red and green indicator lights on his diagram that he may be wanting an indicator LED showing status which might run off the same relay. Just being thorough. smiley

Wayne

East London
South Africa

 

  • No, I am not an Electronics Engineer, just a 54 year old hobbyist/enthusiast
  • Yes, I am using Proteus to learn more about circuit design and electronics
  • No, I do not own a licensed copy of Proteus, I am evaluating it legitimately
  • No, I do not believe in software or intellectual property piracy or theft
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that he may be wanting an indicator LED showing status which might run off the same relay. 

That's good practical warning.  It might be ok with some relays, there are a billion types of construction (ask the phone company)*.  Some may have different switch sections widely separated, but prob not the cheapy China 50 cent relays. A good relay datasheet should specify creep/clear between sections & have ratings to match.

 

*we used to get their scraps when they converted to "electronic" computerized switching.  A two story switching center can hold a lot of stuff! We'd come home with bucketful's of relays of all styles.  I used to have some line-finder "relays"

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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avrcandies wrote:
It shows one form of a 3-way switch

 

Not one DPDT, but two separated switches, when you have two places to switch on/off a lamp. Another wiring is in the picture:

 

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Not one DPDT, but two separated switches

That's called a 3-way switch.  There are a few flavors depending on where the load is with respect to the switches, what wires are available at each box, etc.

For funs you can look at 4-way switches (SPDT at each end, with  DPDT at each point in between).  You can see them in a stairwell*, where each floor (say 6 stories) has a light switch.

 

*if you turn on the lights

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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grohote wrote:

avrcandies wrote:

It shows one form of a 3-way switch

 

 

Not one DPDT, but two separated switches, when you have two places to switch on/off a lamp. Another wiring is in the picture:

 

yes

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If you read #1, there is:

 

which is suspicious. 

Powering RED led current is 2mA. Driving current is <5mA (through 1k resistor).

The coil resistance is 70 ohm, the coil current is 70mA. 

Although board data claims that it will work at 3.75V, it should be tested for each relay.

 

 

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which is suspicious. 

Powering RED led current is 2mA. Driving current is <5mA (through 1k resistor).

Why are you bringing this up?  If the coil current is 20ma max, so what?  What does that have to do with the relay output terminals? 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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This thread is sick from the beginning. Starting with a false picture #4, false relay data, many unnecessary discussions.

 

Both leds are on 5V side, not on relay output terminals.

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Both leds are on 5V side, not on relay output terminals.

Doubtful these status LEDs have anything to do with the actual question (but you never know!)....Otherwise, why the need for a relay?

It's time to hear from the muke to see if they are trying to control a load (either AC or DC), or not.

 

This thread is sick from the beginning. 

I'm calling DR DOS 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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Based on the OP's apparent mains experience i'd prob suggest an Opto protected relay for 15 RS more

https://www.electronicscomp.com/...

 

But that shop's descriptions are horrible ie. Relay can switch 5v/10A when it clearly states 30v/10a DC on the relay ...

Well they got the operating voltage correct ....

 

/Bingo

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Well they got the operating voltage correct ....

They may just be a seller, so take description with a grain of NaCl..you see it especially with sellers listing '328 nanos, drinking straws, ARM chips, and belt buckles. Everything a commodity.

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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avrcandies wrote:
They may just be a seller, so take description...

cum grano salis. Suits them to take 24V relay from the same datasheets, at it is how the driving current becomes 20mA. Because the number look better.

To the uninformed AVR community, it is great, almost for a battery application... to the moment when an AVO meter show 70 ohm

or the current measured is more than 70 mA.

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avrcandies wrote:
especially with sellers listing '328 nanos, drinking straws, ARM chips, and belt buckles.

Don't forget the 28 pin i7's too!

 

FF = PI > S.E.T

 

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avrcandies wrote:

sellers listing '328 nanos, drinking straws, ARM chips, and belt buckles. Everything a commodity.

 

OT I know, sorry. Sounds like the proliferation of companies that came into existence in South Africa because of the Government tender process requirements.

 

I have had personal dealings working for Government (required by the procurement process) with companies that offer a package of IT, cleaning and catering services! Good luck getting critical support at 03:30AM during a disaster period!

Wayne

East London
South Africa

 

  • No, I am not an Electronics Engineer, just a 54 year old hobbyist/enthusiast
  • Yes, I am using Proteus to learn more about circuit design and electronics
  • No, I do not own a licensed copy of Proteus, I am evaluating it legitimately
  • No, I do not believe in software or intellectual property piracy or theft
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WayneZA wrote:
catering services! Good luck getting critical support at 03:30AM during a disaster period!
What do you mean there is no tomato sauce at your table?

Ross McKenzie, Melbourne Australia

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I thought that OP would post this...

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