24 hour Timer triggering a relay for 1 minute, Mark II

Discussion in 'General Electronics Chat' started by jdayer, Jul 25, 2012.

  1. jdayer

    Thread Starter New Member

    Jul 25, 2012
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    Hi All: I am new to this forum and I am interested in building a 12v timer that activates when a button is pushed, stays on for an hour or two and then switches off. I don't think this circuit will do that, it looks like it is designed for minutes.

    My experience in electrical is primarily in machine troubleshooting and repair although I have built a few things in my day. My current solution uses a rather large 12v timer I picked up on e-bay. It works. I just want to replace it with something smaller and neater.

    Thanks

    John
     
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    What output do you want from the timer when it is on? (Volts and amps.)

    And what is your power supply?
     
    Last edited: Jul 26, 2012
  3. jdayer

    Thread Starter New Member

    Jul 25, 2012
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    LEDS and a relay. The switch is connected to door. When the door is closed the system comes on and lights the interior. The relay powers a separate circuit. The whole thing runs less than an amp. When the light is off the box is done. The box is powered by a lithium battery.

    I left the issue in this thread because I think this circuit will work with some modifications. The only other circuit I could find in the forum was for a farm generator, but, that involved a significant number of variables that I don't need to address.
     
  4. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    The standard answer for a request like this is a "one-shot" circuit that uses a NE555 timer. The timer can run on 12 VDC and can supply enough current to operate a relay. It is normally used for shorter periods of time than "an hour or two," but if you don't need fine accuracy, it will work.

    I presume the lithium battery has a 12 VDC output and is automatically recharged from the mains. Does the battery also supply the lights or are they mains powered? Do you already have the relay that switches the lights, and what are its specifications?

    I realize this is a lot of questions, but I assure you that knowing the answers on the front end will expedite the process.

    Here is an example of a one-shot that is triggered by a switch. This particular one is for 10 seconds, but with a couple of component value changes will time for an hour or more.
     
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  5. jdayer

    Thread Starter New Member

    Jul 25, 2012
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    I thought the 555 was only good for minutes which is why I was interested in the 4060...

    I will bread board the circuit you posted and see how it does. That will probably take a week or two (I know that sounds crazy, but, I am really busy and have to find the time).

    I planned on enclosing the timer in a box about 3"x.625"1.25" and hot will be very bad since there would be no ventilation. Also, hot typically indicates an efficient circuit, power being wasted on heat.

    I don't have the specs for the relay handy because I pulled it out of one of my junk boxes. I just measured the current draw in the circuit I have now using my multimeter. My current system works, it is just bigger. It is actually bigger than my box :)
     
  6. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    If you use the CMOS version of the 555 (LMC555), the CD4060, and a MOSFET to drive the LED and relay, there will be little if any heat to dissipate.

    Ken
     
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  7. jdayer

    Thread Starter New Member

    Jul 25, 2012
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    I really can't do electrical design, well, I can design basic wiring harnesses which is essentially what I already built. Do you have a schematic of a circuit using the LMC555, the CD4060 and the transistor?

    The circuit tracecom posted might work and I might build it anyway. It uses the 555, I would just be worried about increasing the resistance of R1.

    John
     
  8. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    I don't think there is a heat issue. If there is a problem with the circuit that I posted, it will be capacitor leakage. I haven't actually built it with the components required to achieve as long a time period as you need, so I can't say for sure that it will work. Using 1000 μF for C1 and 5 meg ohms for R1 should theoretically give about 90 minutes, or so. In addition, the pulse conditioner portion of the circuit probably won't be required. A 4060 circuit might be better.
     
  9. Wendy

    Moderator

    Mar 24, 2008
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    A thread belongs to the OP (original poster). Trying to take over someone elses thread is called hijacking, which is not allowed at All About Circuits. I have therefore given you a thread of your very own.

    This was split from 24 hourTimer triggering a relay for 1 minute

    I got your email, and responded to it.

    Part of the problem with really large capacitors is their leakage goes up as the capacitance increases. Combine this with really large resistors and low currents, and you could have a reliability problem. You may get by with it, but then again, you may not. By bringing the values down to lower values the reliability goes up.

    I need to review your requirements before I can be of much help.

    Power Supply: 12VDC
    Push on, stay on for 1-2 hours, then turn off.
    Load, AC or DC, and current.
     
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  10. jdayer

    Thread Starter New Member

    Jul 25, 2012
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    I didn't realize a modification to an existing circuit is considered hijacking and not allowed.

    12v battery or mains, circuit powers an led and a solenoid. The circuit draws a little less than 1amp max.

    What I would like is to push a button, have the led and solenoid turn on for 1-2 hours and then shut off until the button is pressed again.

    I ordered the materials to build the circuit tracecom posted. When I finish working with it I will post on how well it works. I will probably also play with the circuit Bill posted in the original thread and see if I can make that work. I really don't need very much accuracy in timing.

    Can't hurt to screw around with stuff for a while and if that is what I need to do I can do that.

    Thanks!
     
  11. Wendy

    Moderator

    Mar 24, 2008
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    It is not modifying the design that is the problem, but the attempt to take over an existing thread for your own use. As I said, the thread belongs to the OP (original poster), if someone tried to take over this thread the same thing would happen to them. It prevents major confusion on several fronts. It also prevents a person who started a thread from being drowned out by a hijacker, leaving their problem for which they started the thread unresolved. Much like when you have the floor and someone tries to talk over you, there are rules to prevent it. You can always refer back to the thread that caught your interest in a link, referencing a previous thread is not the problem.

    Being human, moderators can not be everywhere, so we have a little red triangle for members to notify us of abuse, accidental or otherwise, on the top right corner of every post.

    The basic 555 monostable is non-retriggerable. You push the button, it will ignore all further input until the timing cycle is done. Retriggerable is really simple, if that is what you need just let us know.

    Here is the basics of a 555 monostable, along with the theory of operation. It is something I wrote for the AAC book.

    555 Monostable

    Now, if you want to drive a 1 amp load with that a 555 is pretty weak. So you add a transistor like this shown in Example 1. This is not the only way to do it, it is just something i have drawn up.

    [​IMG]

    Some good values for Example 1 to do what you described would be:

    Vcc = 12VDC
    R1 = 10KΩ ¼W 5%
    R2 = 120Ω 1W 5% (you could use 4X 470 ¼W 5% in parallel for this)
    C1,C2 = 0.1µF
    CR1 = 1N4001 (or equivalent, not critical)
    Q1 = 2N3055 NPN power transistor (again, not critical).

    For 2 hours (7200 seconds):
    Rt = 1.5MΩ
    Ct = 4,700µF

    The power draw from this circuit would be around 100ma, to turn Q1 on. I could design something using a MOSFET, and it would be much more efficient overall.

    Not shown are filter caps on the power supply, say 220µF and 0.1µF.

    As I said earlier, due to the large sizes of these timing parts it may not work. If this is the case I can show you how to use the other design to do what you want.
     
    Last edited: Jul 29, 2012
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