Looking for Relay Recommendation

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FlaCharlie

Member
Joined 2004
I know almost nothing about relays so please be patient.

I'm looking for a specific recommendation (part # / specs) for a relay that would be placed in the AC supply to a SMPS. I would be using an IEC that has an integrated fuse and switch and I'd want to put the relay between that and the SMPS.

I'm looking for something that would normally be closed but would open and cut the power if a DC voltage appears on the trigger (not sure if that's the correct terminology). Would this only involve 3 connections or is there more to it than that?
 
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chrisng

Member
Joined 2015
You can use an optocoupled relay module that requires DC power supply.
Schematic, Optocoupled Relay Module
1716002521295.jpeg

If your SMPS required higher current contact rating, you can use a 30A relay module.
 
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Hearinspace

Member
Joined 2008
Paid Member
With the simple relay circuit you are suggesting , once the system powers down and the DC disappears the NC relay would close and the larger circuit power up again.
If the appearance of DC is a fault then you'd want to have a circuit that latches off until you reset it.
 
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MarcelvdG

Member
Joined 2003
Switch mode power supplies usually have huge input current peaks at start up, when the input reservoir capacitor gets charged. You need a relay big enough to survive that. It's mainly an issue if you also want to switch on the circuit via the relay, the inrush current shouldn't spot weld the contacts then.
 
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chrisng

Member
Joined 2015
Hearinspace said:
With the simple relay circuit you are suggesting , once the system powers down and the DC disappears the NC relay would close and the larger circuit power up again.
Click to expand...
I think the auxiliary DC supply for the relay module must be connected before the switch.
Hearinspace said:
If the appearance of DC is a fault then you'd want to have a circuit that latches off until you reset it.
Click to expand...
If that's the case, things get more complicated and maybe a DPDT relay with a reset button is needed to latch.
 
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F

FlaCharlie

Member
Joined 2004
chrisng said:
If that's the case, things get more complicated and maybe a DPDT relay with a reset button is needed to latch.
Click to expand...
Yeah, the presence of DC would indicate a fault so it would need to latch off after it's activated. Also I'd rather have a solution that doesn't require a power source other than AC from the wall.

Does the item you linked latch off? Also, I can't tell if it's normally open or normally closed.
 
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chrisng

Member
Joined 2015
The linked module is actually a 2 channel SPDT relay module with built in power supply.
1716098866952.jpeg


My idea is to use the first relay for latching and use the second relay's normally closed contact to connect to your circuit.

2 CHANNEL LATCHING RELAY.png
 
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FlaCharlie

Member
Joined 2004
chrisng said:
The linked module is actually a 2 channel SPDT relay module with built in power supply.
View attachment 1311896

My idea is to use the first relay for latching and use the second relay's normally closed contact to connect to your circuit.

View attachment 1311897
Click to expand...
Thanks. What's the official name for a "reset button". Tried to look it up at Digi-Key but I don't seem to be finding anything. Got a link or a part #?
 
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