What relay?

Thread Starter

StuManFlu

Joined Sep 15, 2020
39
Hi,

need some advice please. Looking for a relay that will come on with a switched live to connect a permanent live from a different source. Then turn off again with the switched live?

This is to provide a feed separate from the switched live when turning on a fan from a dimmer switch connected to the switched live.

thanks in advance for your help.
 

Thread Starter

StuManFlu

Joined Sep 15, 2020
39
Using a Wi-Fi connected dimmer switch so I don’t think a double pole switch will help.
Looking for a relay that will sit after the dimmer on the switched live. The relay would come on with the switched live but connect power to the appliance from a permeant live from a different source?
 

Thread Starter

StuManFlu

Joined Sep 15, 2020
39
Sorry, let me explain.

so the fan has 2 live supplies one is a permanent supply that drives the fan the other is the switched live that triggers the fan and timer (so the fan runs after switched off). When the light are turned on the switched live triggers the fan and supply’s current until the lights are turned off. When the light are turned off the fan keeps running supplied from the permeant live until the timer turns it off. The problem is because of the dimmer the voltage on the switched live can dip and this effects the fan.

To stop this happening I want to use a relay that is triggered by the switched live but supply's the fan from a different permeant supply that isn’t effected by the dimmer. This will stop the dimmer effecting the supply to the fan as the relay switches to provide a supply from a permeant source.
I just really need to know what this type of relay is called and or some ideas of where to find one?
 

crutschow

Joined Mar 14, 2008
25,247
So it appears you need a circuit to detect the dimmer signal, that then operates a relay.
A TRIAC may work for that with the TRIAC triggered by the dimmer, which controls the relay (or likely could directly power the fan).
 

Tonyr1084

Joined Sep 24, 2015
4,889
Relays have a minimum pull in voltage, meaning the voltage has to be high enough to pull the contacts closed. Once closed, the voltage can drop to some point before the contacts fall open again. In a typical 12 VDC coil relay it may take 8 volts to energize the relay and may hold until the voltage drops as low as 3 volts. Different relays behave differently. I have no idea how much voltage a 120 VAC coil takes to pull in, or how low it can go before it falls open.

I just happen to have one on my bench and have just tested it. It looks like it takes about 60% to fully click in and holds till about 40%. But in the interim it chatters like hell in between. Mostly at 50%. I don't think you're going to find a relay that won't do that. You'll probably have to build a circuit to detect the voltage and energize a switch. Of course my experience is not as extensive as others here.
 

sghioto

Joined Dec 31, 2017
1,313
I think it will cope with the fluctuation in voltage without disengaging?
Will depend on the setting of the dimmer. If too low then the relay may not activate. So from what I read in post #8 the fan has two inputs a fixed or permanent 120vac and a switched 120vac input to get it started, is that correct?
The relay would come on with the switched live but connect power to the appliance from a permanent live from a different source?
EEE Fan control.png
 
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