I need some help with a very basic time delay circuit

Discussion in 'The Projects Forum' started by waspmike, Mar 11, 2011.

  1. waspmike

    Thread Starter New Member

    Mar 11, 2011
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    As you can see this is my first post. Maybe there is a 12 year-old on here who can help me.
    I need a time delay to prevent a second relay from operating when the first one in the chain is monetarily triggered. I need about half to one second delay.


    I have been given two simple time delay circuits for a 12v 1/2 to one second delay. I am trying to keep it simple as I'm not an electronics person. So I tried to avoid 555 timers.

    So far I have built these but neither works. I started with the more complex one then went back to the more simple one. Nada.

    I can only get the relay to activate by "bypassing the transistor. it is as if the transistor will not flow enough current to allow the relay to activate but will pass enough to hold it in.

    Apart from the fact that neither work i don't know enough to be able to troubleshoot to find out why.

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    On the second simpler one I even tried to morph the two by using a separate 12v source to power the relay through the transistor. But still nothing. Coil power consumption is 0.36 to 0.45w

    Are the designs flawed or am I using the wrong components

    I have checked my construction but I see nothing obviously visually wrong.
     
    Last edited: Mar 11, 2011
  2. John P

    AAC Fanatic!

    Oct 14, 2008
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  3. wayneh

    Expert

    Sep 9, 2010
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    I agree with both of John's comments. Note with the second circuit though, that you need a way to drain the cap once power is removed. As drawn you are draining through only the transistor base, and this might take longer than you want.

    With the first circuit, can you trigger the relay by applying power directly to the base of the transistor? If not, then the rest of the circuit is moot and your transistor is backwards (or a PNP?).
     
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    If relay was moved to emitter & gnd, the delay would have a base V range of o to 10V rather than o to .7 V. Add another transistor to make it a darlington pair.
     
  5. waspmike

    Thread Starter New Member

    Mar 11, 2011
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    Sorry about this I feel so helpless.This maybe like someone asking me how to time the cams on an engine when they don't even know how to install the timing chain!

    I have tried to get a transistor to "switch" by applying power directly to the base of the transistor but nothing. I checked the transistor direction and it is OK and I've tried two different C33740 transistors. I am using a 12v battery as a power source for the whole circuit and wonder if 12v or the current is too much is too much for the transistor base?.
    Shouldn't be because the data sheet says CBO and CEO 50 and 45v respectively?
    This maybe like someone asking me how to time the cams on an engine when they don't even know how to install the timing chain!
     
  6. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    If you connected +12 without a current limiting resistor to base= Poof. Would help to know what pull in voltage of relay is, also coil resistance? Maybe about 300Ω?? If pull-in is more than 9V , following thumb n will not work, then to plan C Do you have a multi meter? Do you have a slightly higher V power supply than 12V?
     
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