RELAY HELP: power ON to momentary ON ; power off to momentary ON

[Bob T]

I would like to assemble something which plugs into a remote controlled 110v wall outlet.
When the AC is on, a relay momentarily closes a circuit (presses a button and releases.. 1 second. )
When the AC is off, a relay momentarily closes a circuit (presses another button and releases, 1 second)

I'm thinking of using off-delay relays, however I cant figure out the last half of this problem... perhaps use a capacitor that charges during the AC ON to activate second off-delay relay when the AC is OFF?...

Any help would be appreciated.

 

[ADWSystems]

I don't think your going to be able to AC directly due to part 2 (caps don't store AC power). A small wall wart to provide DC power will solve that but create another. A 1 second hold time is a long time.

I'm just roughing this out, I have not put pen to paper. AC power comes on, DC voltage comes up, at some point relay 1 will turn on. The first trick is to turn it off after 1 second. I'm thinking an transistor drive on the relay with an RC combination in the base. As C1 charges the base drive will drop, and at some charge voltage the transistor will turn off and thus turn off the relay.

The second trick is to have relay 2 turn on when AC is lost and stay on for one second. This might require a two stage implementation. The first stage to detect the PS voltage drop, which activates the second stage to activate the relay. This time a large capacitor will be needed as it will be the only power source for the relay. A 5V relay with a 100 ohm coil is going to draw 50mA. Assuming a 10% release point, the capacitor will need to supply 50mA for 1 second and only lose 0.5V. With i=C dv/dt where dt=1, and dv=0.5 gives C=0.05/0.5=0.1F capacitor.

Don't forget to place current limiting resistor between the off-relay capacitor and the power supply. Without the current limiter, you have two issues. First the big cap will hold down the PS while it charges which will affect on relay operation. Secondly, it will charge VERY fast either damaging it now or with repeated use and eventually it will blow.

Are the buttons, the same button or two different buttons?

 

[alec_t]

What power source is going to energise the relay when the AC outlet power goes off?

 

[cowboybob]

Welcome to ETO, Bob T!

<EDIT>Assuming you have a power source when the "remote controlled outlet" is OFF;

A "window" comparator driven relay circuit would work for you.

With what level of circuit assembly are you comfortable?

 

[Bob T]

the buttons will be two different buttons. They are buttons on an RF remote. (On button is ON the other is OFF). Using an adapter for DC is not a problem, I was contemplating the idea myself. I suppose I could have a separate, constant on, power source when the remote outlet is off, if need be...but would love not to!

 

[moty22]

Hi Bob.
As I understand you are not putting 2 buttons on your device, you are wiring the relays contacts to the switches on the RF remote.
Your first idea of charged capacitor is ok. You need to charge a cap anyway for the relay that pulls on power on. If the cap is big enough it can hold the second relay pulled for 1 second. If you use reed relay then the a cap of 1000uF will be big enough. You will need electronics to sense and switch the relays when the power changes. I'm afraid I'm not good enough for that but there are many members who can help when they know exactly what the task in hand is.

 

[KeepItSimpleStupid]

I did a "similar" thing in the 80's. I needed as you did to:

1. "Turn-on" a device (timer) with a pulse when a LED illuminated on the source.
2. Turn OFF a device (audio equipment on button (essentially a keypad) with a pulse from the timer when the timer went off.

I used an opto-FET and a small current regulator so any pules from about 3 to 32 V would work.

It worked for the most part, BUT a power glitch would sometimes leave the source device powered up after the glitch.

you are wiring the relays contacts to the switches on the RF remote.

Don't! Use an OPTO FET. These https://www.newark.com/excelitas-tech/vtl5c1/optocoupler-resistor-2500vrms/dp/43F885 devices are easy to work with. An OPTOmos relay will generally work too,