Relay to trigger fan overboost

[Bobbyboo]

My ventilation unit requires a no-voltage switch to trigger the boost function which should be triggered when two light switches are switched on. Unfortunately using a double pole (DTST) switch is not an option (would require changing a large number of switches), so I am trying to find another way of achieving the same thing. My idea would be using a relay:

- 2x 230V light circuits each with a relay

- relay switches the no-voltage circuit which is connected to the control unit of the fan

 

Ie, when either light is switched on, a connection in the no-voltage circuit should be established, but no current should be transferred onto the no-voltage circuit.

 

I plan on using 2 of these relays: https://docs.rs-online.com/5c2a/0900766b816d4f15.pdf (26.01 version) - would this work?

[Nickfromwales]

Hi. 
Yes, as long as the coils are 230VAC rated then you’re propel is sound. Just be sure to have good segregation of the cables at the relays, so you cannot ever get 230VAC going down the zero volt side. 

[Radian]

Why have you shown the relay coils in series with the lights? 

[Temp]

+1

 

 Should be in parallel with the lights.

[Radian]

If you wanted a much lower cost solid-state solution using an optocoupler you could knock up a circuit like this:

 

 

C1 can be any low voltage electrolytic e.g. 6V, C2 & C3 need to be 400VAC types. R1 ought to be 1W, R2 1/4W and just about any sensitive opto should do if PC817A hard to find.

D6 is a 4.7V 1/2W Zener.

 

You would need to be confident in constructing a mains powered circuit - I only suggest this if you have the appropriate skills!

 

...And I'm assuming the volt-free input is low voltage control!!!

Edited December 23, 2021 by Radian

[Bobbyboo]

 

9 hours ago, Radian said:

If you wanted a much lower cost solid-state solution using an optocoupler you could knock up a circuit like this:

 

Thanks! In my case, using relays will be fairly easy and hassle free. The cables are all already in place as they previously were connected to DGST switches, so it's a 10 minute job and all I need to do is add 2 relays, 20cm of cable and a junction box for under £20.

 

12 hours ago, Radian said:

Why have you shown the relay coils in series with the lights? 

 

My mistake. They should be in parallel! 

[Radian]

1 hour ago, Bobbyboo said:

Thanks! In my case, using relays will be fairly easy and hassle free. The cables are all already in place as they previously were connected to DGST switches, so it's a 10 minute job and all I need to do is add 2 relays, 20cm of cable and a junction box for under £20.

 

No worries. Because you were buying from RS I guessed you might be up for doing a bit of electronics ?