How to monitor the health of a relay and it's contacts

Other Hardware Sensors
1

Hi, I have a challenge and hope someone has and idea how to solve it.

I want to monitor the health of a relay by monitoring the state of relay contacts in relation with the state of the coil. I want to see if the contacts are open or closed when the coil is energized or not energized. I want to do this with an Arduino. It must be something like you see in the drawing below.

Can you tell me if there is a component or sensor that can do this. Let me know what idea you have how this can be done.

Thanks

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2

Some ideas

Use a current sensor, clam version.

Add a 120V light across the motor and check this (ON/OFF) with an LDR.

Vibration sensor on the motor.

If the relay is multi switch (?( and has one free it is straightforward.

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3

AC opto coupler across the relay contacts.
That of course will only work when a load is attached and there is mains power.
Leo..

4

Another relay? One with a 120V AC coil.

5

That doesn’t work the schematic doesn’t show it, but the load is connected to different sources. Each source is switched by a relay switch but never at the same time. It’s part of a transfer switch. I want and need to see the state of the contacts when I activate the one of the sources.

6

Thanks Wawa, That sounds interesting. You mean an optocoupler that will be off when the contacts are closed and activated when the contacts are open correct?

7

that’s not gone work unfortunately

8

An AC opto coupler can detect voltage across the contacts, which will be an indicator if the contacts are open or closed. The H11AA1 comes to mind, but there are many others.
Leo..

9

It’s part of a Transfer switch made using two independent relays or contractors. I don’t want to switch if the contractor connected to the grid is hanging because of mail functioning contacts. For that reason, I need to see the state of the contacts to only switch if the contractor to the grid has disconnected from the load. It’s a security issue.

10

Yes it is going to work

11

You should monitor the grid voltage, the off grid voltage, the load voltage and the relay TTL signals. From those readings you can determine the state of you entire system at any time and locate any faults.

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12

If you had a relay on a bench which you thought might be faulty, you would do some basic checks on the coil, powered up or unpowered, then test all the contacts for operation and resistance.

You want to do that in situ. As has been said, you can use spare contacts as watchdogs, in a failsafe setup. Monitor the load.

A lot of relays and contactors have test buttons and flags and industrial contactors have plug in modules for extra functions. A useful addition is a built-in LED that shows when the coil is energised.

How critical is this?

13

Take a look at :

Mains voltage detector (neon bulb based for 230v door bell repeater)
Found under: Projects - Showcase.

ffur

14

I would use a simple rectified transformer and place it parallel with the load. You could also use a small charger as the sensor. Then place a 27K resistor in series with the Arduino input, this protects if the load is on and the Arduino is off.

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