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Relay to trigger fan overboost


Bobbyboo

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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?

Screenshot 2021-12-23 at 16.42.04.png

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

 

714589678_Screenshot2021-12-2322_24_59.thumb.png.7dc7e41474b6580446194893b93710d7.png

 

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 by Radian
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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! 

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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 ?

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