Hi, I'm New to the Chat forum - Looking some advice on door contact switches and relays?

[M17BMD]

Hi,

I am new to this and just currently 2nd fixing a new build house at the moment.

I have a small pantry in a new house which has been designed with insulated walls and doors, etc. with the idea being that it is kept at a different temperature to the rest of the house to store food. There is an air duct coming at the bottom to deliver fresh cool air and and inline fan and duct at the top of the unit to circulate the fresh air through the cupboard space. The fan should normally be in the off position but only comes on for 5 minutes after the doors have been closed.

I would like that when the door is opened, the interior light comes on and when placed back in the closed position the light is turned off and a signal is sent to the inline fan to turn it on. The inline fan has an overrun timer built in so I assume that as long as a signal was sent to the fan and the fan had a live feed that this would allow it to start up and then turn off automatically rather than the switch sending the live feed?

I would ideally like one type of door contact switch to make this all work but wonder if this would be possible?

Any help would be greatly appreciated.

Thanks, Brian

 

[Sharpend]

Just put a motion sensor switch in place of the light switch. Then it will sense when you open the door and turn light on and turn it off when you close the door.
If the fan is working now then what needs changing with it?

 

[M17BMD]

Thanks for your reply.

Yes but I want the fan to be normally in the off position and it would only come on when the door is closed and then runs for the 5 minutes on the overrun timer to cool the space back down again.

I need to get a switch or motion sensor to complete both functions - Turn the light on when door is open then when the door is closed the light would switch off and a signal would be sent to the fan to come on for 5 minutes.

 

[Richard-the-Ninth]

As Sharpend says, it would be easier to leave the fan running 24/7
With that in mind you only need to turn the light on/off, a PIR would be no use as it would see the draught caused by the fan, what you need is a "Fridge switch" Click here Just like a fridge it only works when the door is open.

If you really want the fan to stop AND the light turn on, you would need a change over switch Click here But its a lot of grief for no gain.

 

[Sharpend]

Sorry I thought the fan was already designed and working.
Let me think about this for a mo…

 

[Sharpend]

As Sharpend says, it would be easier to leave the fan running 24/7
With that in mind you only need to turn the light on/off, a PIR would be no use as it would see the draught caused by the fan, what you need is a "Fridge switch" Click here Just like a fridge it only works when the door is open.

If you really want the fan to stop AND the light turn on, you would need a change over switch Click here But its a lot of grief for no gain.

This would involve a bit of reconfiguration of wiring. The fan would need a live supply momentarily to activate fan then it will run on for set time on overrun.
What the fan needs is a retractable switch that makes and breaks on door closing?

 

[Richard-the-Ninth]

Yes, Sharpend, it does, which is why I also suggested the 2nd switch.

 

[Sharpend]

But wouldn’t that put a Permanent supply to fan at some point which would leave fan running all the time?

 

[Richard-the-Ninth]

Damn, you are not wrong Sharpend. (I was thinking more of the light )

Still an easy one to solve.

Have TWO of the first switch.
It is easier to do, easier to understand and costs less than a relay, timer, power supply and box to mount it in.

​

 

[M17BMD]

Thank you both for your feedback.

Do you think then that a limit switch to control the 2 circuits (1NO + 1NC) would work in this situation or would you be better with a separate fridge type switch to compete each of the functions?

Thanks

 

[Richard-the-Ninth]

As I said, Sharpend spotted my error, I was thinking the fan would run all the time, but stop when the door opened.

Since the fan is to switch off via its own timer, go with what I then said

Have TWO of the first switch.
It is easier to do, easier to understand and costs less than a relay, timer, power supply and box to mount it in.

One switch operates the light, one switch operates the fan.

 

[M17BMD]

Thanks for coming back to me.

The 2 switches make sense to me as I have a set of double doors into the space and I could mount a fridge switch on each door, However I'm not just quite making sense of the switch for the fan as I would only need to be sending a quick signal to the fan to engage the overrun timer as I don't want the fan to run when the door is opened and remain off until the door is opened and then closed again so would this type of switch allow this to work ok?

Would I need a push to make for one function and a push to break for the other?

 

[Richard-the-Ninth]

You will have to put both switches on the same door, if you don't and open "the wrong door" the light will not come on.
With the other switch operating the fan: The fan will start as soon and for as long as the door is open. When the door is shut the fan will continue to run until the over run timer stops it.

Anything else will require timers and a relay or two and it gets expensive.

 

[M17BMD]

I have a set of double doors leading into this space and both would have to be opened to access the cupboard as they are quite narrow doors so I could work a switch on each door. The problem I have with the fan coming on when the doors are open is that it kind of defeats the purpose because it will draw warm air in from the kitchen when the doors are opened which would also cause a draft.

I had a chat about this with an electrician last night and he is currently looking at a the following type of relay: https://uk.rs-online.com/web/p/latc...6E6669673D3026&searchHistory={"enabled":true}

Have any of you had any experience with this relay and is it something that you think would work in this instance?

 

[Sharpend]

I think you will need one of these.
https://techna.co.uk/techna-timer-relays/
Reason being you can have power to the switch when door closed for fan then set timer to shut off switch live to fan so it runs on over run.
Once timer runs out the relay will reset.

 

[M17BMD]

That's great, thank you.

I have spoken to Techna about this timer relay and they believe that it should be the correct relay for this application so I have now ordered one and it should arrive later this week so I will let you know how I get on.

Once again, many thanks to both of you for your help!

 

[M17BMD]

Hi,

I just wanted to come back on and let you know that the Techna timer relay works well and has solved this problem for me so once again many thanks for your help. I was able to pair this up with a 'push to make' and a 'push to break' door switches which allow the fan and the LED light strip to be activated.

I do however now have a slight issue in integrating the door switches into the cabinet and I was wondering if it would be possible to use a PIR sensor with an L1 & L2 function to allow one PIR sensor to act for both the fan and the LED light strip or alternatively would 2 separate PIR sensors be able to complete the functions of the 2 door switches?

 

[Sharpend]

One PIR will do both. Put switch wires out of pir to led light and fan.

 

[M17BMD]

Thanks for your response, but will the one sensor allow the light to come on when motion is detected (i.e. when doors are opened) and then a pulse signal to be sent to the relay to engage the fan at a later stage (i.e when the doors have been closed again) or would you just set a time delay on the relay for the fan?

 

[Sharpend]

How have you connected the relay?