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

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Piet de Pad

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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
1766020032675.png
 
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Seriously? Ok, I'll play the game:

Put a voltage divider across the load with a diode and cap.
--- Updated ---

barry said:
Seriously? Ok, I'll play the game:

Put a voltage divider across the load with a diode and cap.
Click to expand...
You could also use an optoisolator.
 
Last edited:
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barry said:
Seriously? Ok, I'll play the game:

Put a voltage divider across the load with a diode and cap.
--- Updated ---


You could also use an optoisolator.
Click to expand...
I didn't show that in the schematic, but the load can come from different sources. Each individual switched to the same load but never active at the same time.
 
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Piet de Pad said:
the load can come from different sources. Each individual switched to the same load but never active at the same time.
Click to expand...
I don't know what this means, but if you connect the optoisolator or rectifier circuit or whatever between the bottom contact and ground, it doesn't matter what the load is. Contact open: 0V, contact closed 120V.
 
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lichur_bagan said:
Here you may get some idea. https://uk.rs-online.com/web/content/discovery/ideas-and-advice/auxiliary-contacts-guide?
Click to expand...
Good article I read it and yes that a way to do it but it requires special relays but good to know thanks,
--- Updated ---

barry said:
I don't know what this means, but if you connect the optoisolator or rectifier circuit or whatever between the bottom contact and ground, it doesn't matter what the load is. Contact open: 0V, contact closed 120V.
Click to expand...
I agree with you assuming there is a grid available detection you can do as you propose a break before make detection in this way. If I see after deactivating the main grid relay a short zero voltage over the load I must assume that is caused by the opening contacts of the relay and the contacts are not fused together. I can then activate the relays that connects the backup source to the load. however ......

You suggestion does not work when I have a grid blackout. When I detect that blackout, i can't see when I deactivate the grid relay if its contacts are fused together or not. So if i activate my backup the is a very small probability that I connect my backup source to the grid and the load.
 
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Piet de Pad said:
Good article I read it and yes that a way to do it but it requires special relays but good to know thanks,
--- Updated ---


I agree with you assuming there is a grid available detection you can do as you propose a break before make detection in this way. If I see after deactivating the main grid relay a short zero voltage over the load I must assume that is caused by the opening contacts of the relay and the contacts are not fused together. I can then activate the relays that connects the backup source to the load. however ......

You suggestion does not work when I have a grid blackout. When I detect that blackout, i can't see when I deactivate the grid relay if its contacts are fused together or not. So if i activate my backup the is a very small probability that I connect my backup source to the grid and the load.
Click to expand...
You said nothing in your initial post about detecting the contact state when there's no power.

The only way you can tell if the contact is closed or open is to put a voltage across it.
 
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