# Timer Relay

Discussion in 'General Electronics Chat' started by Lanz, Jul 29, 2009.

1. ### Lanz Thread Starter Active Member

Oct 30, 2008
153
0
Hi guys i need a timer relay for my car.
I already browse the forum but still confused.
I need a 555 based power-on and power-off time delay relay(separated circuit).
The time must be adjustable and i need a regulated power supply for the circuit.
I also need to know how to calculate the timing of 555.
I know its depend on RC,but i dono how to calculate.
If got separated power-on and power-off time delay relay circuit picture,it will be easy for me to understand.

Last edited: Jul 29, 2009
2. ### KMoffett AAC Fanatic!

Dec 19, 2007
2,574
230
Lots of 555 info including fill-in-the-box timing calculators.

Ken

3. ### alitex Active Member

Mar 5, 2007
122
0
you can control in the time by choosing values of capacitor and resistance that you are use it in the timer through t=0.69(RA+2RB).C

4. ### Lanz Thread Starter Active Member

Oct 30, 2008
153
0
Well thanks for the info.
I had googled and find some info abt 555 but i never found the circuit that i needed.
I desperately need power-off time delay relay.
Anyone can help me with the circuit?

5. ### KMoffett AAC Fanatic!

Dec 19, 2007
2,574
230
What length of delays are you looking at..1 Sec?...1 minute?...? Can the power-off-delay circuit be powered by another source while it delays shutting off...whatever.

Could you elaborate on the problem you are trying to solve with the delay timers? It could make a difference in the solution.

ken

6. ### Lanz Thread Starter Active Member

Oct 30, 2008
153
0
Well actually im trying to do a turbo timer for my car.
I know that its cheap n available at the shops.
But i want to do a simple one by myself to learn.
If there is no 555 power off time delay circuit available,i can acept other IC circuits as long its not expensive.

7. ### KMoffett AAC Fanatic!

Dec 19, 2007
2,574
230
Since I'm not into engines...how long a delay are you looking at?

Ken

8. ### Lanz Thread Starter Active Member

Oct 30, 2008
153
0
The timer is not connected to engines.
Its only connected to the ignition.
I need an adjustable timing to maximum 5 minutes.
Below,I give you an example for 10 seconds power off delay.
After you stopped the engines from running by turn off your ignition key,this timer will start working which means this circuit will make the engine running for 10 seconds(the key ignition had been turned off) and then turn off the engine after the time ends(10 sec).
The relay will take care of switching the ignition.
Now i just want the circuit only.
Can you help me with the circuit Kmoffet?
I would be very thankfull to you if the circuit works well.

9. ### KMoffett AAC Fanatic!

Dec 19, 2007
2,574
230
Probably...but it may take a little while before I can get back to you.

Ken

10. ### Lanz Thread Starter Active Member

Oct 30, 2008
153
0
No problem Ken.
I'll wait for ur circuit.
If cnt done with 555,any other IC based circuit also can as long as it does not cost me much.
Appreciate ur replies.Thanks

11. ### vindicate Active Member

Jul 9, 2009
158
0
I think what you want is a 555 Timer in Monostable mode with a adjustable resistor.

12. ### Lanz Thread Starter Active Member

Oct 30, 2008
153
0
Maybe u're correct.
But i dont know where to modify it as i want.
Most of the circuit available in the net is power-on circuit.
I need power-off circuit.

13. ### KMoffett AAC Fanatic!

Dec 19, 2007
2,574
230
vindicate is right...but it will always have to be powered...even after all the delay ends. With a CMOS 555 this is only a very small current drain on your battery. Power for your delayed device will come from the ignition when it is on, or from the timer's relay. This is done with a pair of diodes the act like a logic OR gate. When the ignition is shut off the monostable's trigger is pulled low and turns on the delay relay for X seconds. The switch over time for the power will depend on how long the relay contacts taue to "make"...usually max of ~0.1 seconds.

ken

14. ### Lanz Thread Starter Active Member

Oct 30, 2008
153
0
I dont understand much on ur explanation but able to understand a little.
All rite,now we change the circuit to always powered.
The ignition key(OFF position) will trigger the circuit to be ON.
The circuit will keep the relay energised to keep the engine running.
After 10 sec,the relay will be deenergised to turn OFF the engine.
Or u got any better idea?

15. ### KMoffett AAC Fanatic!

Dec 19, 2007
2,574
230
You have it exactly! I'll try to throw together a schematic.

Ken

16. ### Lanz Thread Starter Active Member

Oct 30, 2008
153
0
I have the idea but dono how to make it electronically.
Thats it Ken,a schematic is what i want.
The circuit must have variable timing from 10 seconds till 5 min range.
Either controlled by VR or switched resistor.
And a switch to turn off/on the circuits.(Usually the emergency brake switch is used for turbo timers)
Give me ur best.

17. ### KMoffett AAC Fanatic!

Dec 19, 2007
2,574
230
How much current is required for the device(s) that the delayed circuit controls? This is about sizing the diodes and relay.

Ken

18. ### Lanz Thread Starter Active Member

Oct 30, 2008
153
0
Well i dont know abt that.
But it supposed to be connected to car battery.
As i got info from other site's,a minimum current of 200mA is needed to energise a relay.
Im going to use car relay for this which is 12V 30A.

19. ### KMoffett AAC Fanatic!

Dec 19, 2007
2,574
230
OK, this is bench tested only. I have not made any effort to protect the circuit form the bad electrical environment in an automobile. Perhaps others that are more familiar with that can jump in. Note the break in the wiring from the ignition switch to the ignition circuits.

When the ignition switch is ON Relay 2 is powered through D3. This maintains its contacts closed and connects the ignition circuits to +12V.

When the ignition switch is turned OFF it triggers the timer. Relay 1 is turned on. Relay 2 tries to open, but the timer keeps Relay 2 closed through Relay 1 and D4.

When the timer times out Relay 1 on opens, causing Relay 2 to open, shutting off the motor.

When the ignition switch is turned ON, Relay 2 is again powered through D3 and the ignition circuits are powered.

I also didn't include any fuses.

Ken

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20. ### KMoffett AAC Fanatic!

Dec 19, 2007
2,574
230
Or you could replace the small relay (Rely1) and a diode (D2) with 3 resistors and two transistors.

ken

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