How to extend relay working time without controlling signal

Question

I have following electric schema which works on 230V AC.

I am using remote controlled relay(RCR) to start and stop the engine. The problem is that I am not sure about wireless signal quality and I afraid that it may end in the situation that engine has started but not stopped.

Because of that I have safety switch which is time relay(TR). Circut works like this:

1. TR has NC connectors which are giving current to RCR even when it's turned OFF.
2. When RCR receives swiich signal it gives controlling signal to TR and powers the engine.
3. Engine is running and TR is counting time to change NC connector to open.
4. When TR reaches the time it switches NC connector to open.
5. When NC connector is open three things happens:
   • engine stops working
   • RCR is turned OFF
   • TR is turned OFF

And here it is a problem. When TR is turned off NC connector returns to the state closed. Because of that RCR is back online. But the time it happens is so short that it's not able to return to it's default state which is ON, so the system is back in point 2 instead of 1.

My question is how can I extend the time of TR open state? Naturally it will mean that I need some sort of "UPS" on TR controlling line, but I need something cheap that will last for 1-2 seconds(maybe even less). Should I use some sort of capacitor?

I am kind of new in this field and some terminology may not be correct or some asumptions may be wrong.

UPDATE

I found some relay which holds a state without power for some time. I have no idea how it is called but it works like this:

When it receives signal it changes connector states and when the signal is gone it holds the state for given time. I've changed my circuit a bit to work with this and it looks like this now:

And works like this:

1. TR is giving power to RCR
2. When RCR is switched on it gives power to engine and hold state relay( HSR)
3. HSR is controlling TR control signal.
4. When HSR receives signal it switches TR counter
5. When countdown is finished RCR is turned off.
6. HSR is no longer recieving signal, but it still holds state for desired time.
7. RCR returns to default state.
8. HSR countdown finishes and it returns to default state.
9. Whole circuit is in starting state.

This solution is much cheaper than adding additional 4 relays.

UPDATE 2

I have an another idea, but I am not sure if it will work. My time relay is 12÷264 V AC/DC. I am considering using AC/DC 230/12V transformer and some capacitors for holding state. I have two capacitors 470uF 200V but I am not sure if they are big enough. Using transformer and capacitors would not require additional delayed timer.

Answer 1

I checked out the remote switch description and it is certainly a weird device. They claim it can adjust the brightness, which means it is not just a relay. Something else is going on inside, maybe a diode to cut power in half. So, I would not recommend shorting the input and output of it.

Anyway, I don't think it is possible to do what you want only with parts that you have already. Here is the simplest circuit I could come up with. It requires another timer and a couple of NO relays. 1) Initially NC contacts of Timer 1 provide power to remote switch. Everything else is OFF.
2) When Remote is activated it triggers Relay 1. This relay powers the load and starts both timers.
3) In addition, Relay 2 is triggered via NC contacts of Timer 2 and it immediately bypasses Relay 1 locking itself (and both timers) in ON state.
4) Timer 1 is set to very short delay. After this delay Timer 1 disconnects Remote switch, giving it plenty of time to reset to OFF state.
5) When remote switch fully shuts down it releases Relay 1. However both timers and Relay 2 remain under power provided by Relay 2 bypass.
6) When timer 2 reaches the end of its own delay it disconnects Relay 2. Here is where magic happens - unlike your circuit, timer does not cut it's own power (which causes it to reconnect right back). Instead it cuts power to relay coil, and since both timer and relay are powered by relay itself it is guaranteed that by the time NC contacts reconnect there will be no electricity to conduct.
7) Timers are powered down, Timer 1 restores power to remote switch, and we are back at initial state.

UPDATE:

Here is a photo of wireless remote I found here. It shows the switch controlled by grey slider under the button, which means the remote is capable of transmitting at least 2 different commands. What the receiver does with them is completely different question.

I suggest taking the receiver apart and tracing the connections from the outputs. If they go straight to the inputs with relay interrupting Hot line then you can cut those traces and short them on the relay side. This will give you relay contacts isolated from the inputs so that you can use Remote switch as Relay 1 on the schematics above. Then you'll only need one more relay and one timer.

Of course if there are other parts connected to output traces it would require a bit more tweaking. Also it would not work if the default state of the relay is ON when power is not applied to the remote. You can check this without cutting traces by testing the connection between input and output hot lines.

Answer 2

It turned out that solution was simpler than I thought. I've attached AC/DC 15W LED Transformer and it works. Even when I manually turn OFF the remote switch the diode showing power on relay is turned ON for a short moment( ~ 1s) and it's enough. Here is how it looks: