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    This time delay relay circuit is built with IC NE/SE555, produced by Intersil which contains a precision timer. Stability to temperature variations is 0.005 %/oC. In the circuit diagram, the IC works as a monostable multivibrator. It is set by operating the key Dr1. With Dr2 you can reset the assembly any time you desire.

    Time delay relay operation

    Pin 3 provides (after setting) a positive rectangular pulse, whose amplitude is approximately equal to the 12V power supply voltage. This output should not be charged with more than 200 mA over a period of time.

    Pulse width can be calculated with the formula:

    t = (R2 + Rp1)*Cs1

    In this formula t is in seconds if the R2 and Rp1 values are set in ohms and Cs1 is in Farads. Cs1 is the switched capacitor to potentiometer P1 by the S1 switch. Lighting time is set roughly in the decade with S1, while P1 serves to fine tune.

    Time delay:
    S1a = 0.1 … 1 s
    S2b = 1 … 10 s
    S2c = 10 … 100 s
    S2d = 100 … 1000 s
    S2e = 1000 … 10000 s

    For the Reed relay, by whose contacts the lamp is connected and disconnected, the following conditions must be met: operating voltage does not exceed 12 volts and current draw is not greater than 200 mA. If Reed relay’s working voltage is below 12 volts, then you can connect a resistance Rx in series with the relay’s coil.

    Eventually it can be used a triac in place of the Reed relay. In this case the gate is controlled by Rx (here Rx = 150 ohms).

    You should to consider a proper insulation of the time delay relay installation and wiring.

    Time delay relay circuit schematic

    time delay relay circuit schematic

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    20 Responses to "555 Time Delay Relay Circuit"

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    1. Heloo, NICE circuit idea ! Can you or someone please tell me, will this re-set itself? Meaning, we know it will delay the on time, but will it also delay off time as well and restart the cycle? I guess I could build two seperate circuits to re-set it but seems like it would be a waste to do so if modifictions already exist to accomplish the same results,,Thankyou

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    2. I asked that question on thee 10th of November, 2010,,, today is thee, 31st of December 2010. After almost two months I have tried various other design’s via transistor and thee ever famous 555. I have yet to finish a totally simple circuit, because I HAVE NO EXPERIENCE, and have no ANSWER TO MY 1st question. WHATS THE POINT OF THIS PAGE IF NO ONE MONITORS IT?

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    3. Ed How long do u want the circuit to stay on before turning off and do u want this to cont all the time off on off etc

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      • Well technology got me, I lost my computor due to virals. So a belated thank you for your response. I got it too work, I found one on “chemelecs” electronics projects page builf it, analyzed why it works and move into modification of a simpler single 555 version of my own. The it work fine on the bench,,I found it lose its stability in the truck I built it for too siwtch on and off and on a relay conected EFIE,, “electronic fuel injection enhancer” installed in series w/ O2 sensor to OBC,, think it was picking up “hysterious?” Any Idea?

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    4. Hi……….. i want 6 hour timer circuit diagram. HELP ME please….

      Regards.
      Sudharson

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    5. Similar to Ed, I’m looking for a delay on/delay off circuit — Controlling a pump, the input (a pressure activated switch) tends to cycle for a few seconds after either an on or off action and i want to damp out these oscillations after *either* transition. This circuit gets me half way there….any ideas for ther other half? -J

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    6. this is good man!!! i i finally to do this right… basis the time relay… you must depending the capacitor.. this is great and meaningful!….

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    7. what is B25C500 ??

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      • Jim Keith Jim Keith says: on October 1, 2012 at 1:31 pm
          member

        B25C500 is a full-wave bridge rectifier. Virtually any bridge rectifier will work for this application, or you may make your own with (4) 1N4004 rectifiers. Just remember that all arrows point in the same direction or to the right in this case.

        Regarding the 10,000sec time delay, I would dispense with the 4700uF capacitor because it is very unlikely that the 2M resistor can charge a capacitor of this size due to its leakage current.

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    8. nice work ! perfect for my subject proposal.
      In place of the Reed relay, what TRiac rating i’ll be use ? thanks !

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    9. and how i connect the triac in the circuit ? sorry i’m quite noob, this is for my minor subject :)

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    10. can i replace:
      1. 500k potentiometer on 2M pot
      2. BT 136 on reed relay
      3. 12v 200mA only transformer

      thanks !

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      • Jim Keith Jim Keith says: on October 3, 2012 at 10:00 am
          member

        These changes are OK. Another issue I have with the circuit is the absence of a back diode across the relay coil, so place a 1N4004 diode across the relay coil with the cathode up. The diode provides a path for the inductive discharge rather than through the IC. While it may work without this diode, some 555 devices may function properly.

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      • thanks for your reply !
        i replace my pot to 1Mohms.
        also, if i replace BT 136 on reed relay, correct me if i’m wrong on pins: M1 to ground; M2 to AC load; Gate to 150ohm resistor.
        with your diode on pin GATE pointing up.

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      • Jim Keith Jim Keith says: on October 13, 2012 at 8:38 pm
          member

        Looks good to me. Let us know if it works OK.

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    11. teach me how to connect the triac on the circuit help me.it cant delay or even turn on a fluorescent bulb.

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      • Jim Keith Jim Keith says: on October 14, 2012 at 2:06 am
          member

        Troubleshooting tips:
        Connect resistor and LED to pin 3 of 555. If it does not light as expected, find wiring error.

        Apply approx 100mA DC gate signal to make sure that it turns on in both polarities. Do this by connecting 100Ω resistor between gate and +12VDC. This should turn on TRIAC. Test with incandescent lamp if you have problems with fluorescent lamp starting properly.

        Diode previously mentioned is for relay coil. Since the TRIAC has no inductance, no diode is required.

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      • therefore I have 2 resistors connecting on GATE of my TRIAC. parallel 100ohms 12vdc to GATE with RX=150ohms from pin 3 to GATE ?

        RX got burn maybe because I connect A2 to 12vdc ground or i’d use 1/2 watt to all my resistor.

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      • Jim Keith Jim Keith says: on October 14, 2012 at 6:09 am
          member

        100Ω is for experiment only while 150Ω is disconnected.

        Yes, swapping A1 & A2 could burn out both resistor and 555. TRIAC may not survive either.

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    12. Digi Components says: on December 18, 2012 at 9:57 am

      Some content not understand, tomorrow to see it again.

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