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Need a timer diagram?

Discussion in 'General Electronics Chat' started by zone97, Jan 28, 2009.

  1. zone97

    zone97 New Member

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    Here is a close up of my protoboard.

    I used an LED to simulate where the pump will be.
     

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  2. duffy

    duffy New Member

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    Voltage measurements???
     
  3. zone97

    zone97 New Member

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    Where would you like me to check?

    on the diode ----12v--|<--6.9v----

    The 6.9 starts at 0 and rises but I guess it doesn't rise enough to release the relay.
     
    Last edited: Feb 10, 2009
  4. dave

    Dave New Member

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  5. zone97

    zone97 New Member

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    HALLELUJAH

    Damn transistors were backwards.

    Scratch that, works great thanks for the help.
     
    Last edited: Feb 10, 2009
  6. zone97

    zone97 New Member

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    One last issue, I built it and it works, but when the motor is attached. When the relay gets close to the time to release it "chatters" and never releases.
     
  7. duffy

    duffy New Member

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    Do you have a protection diode across the motor? See the one on the relay coil? Try putting one on the motor the same way.
     
  8. duffy

    duffy New Member

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    No, wait - take D1 out of the circuit and try it again. This is going to be ground bounce from the load retriggering the device. Too much load for the power supply, pulls the supply down, bounces up again when disconnected. Removing D1 will make the "off" time as long as the "on" time.
     
    Last edited: Feb 10, 2009
  9. zone97

    zone97 New Member

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    Sorry, I took d2, let me short out d1 and see if that helps.
     
    Last edited: Feb 10, 2009
  10. duffy

    duffy New Member

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    What is the difference between the power supply voltage when the motor is on and when it is off?
     
  11. zone97

    zone97 New Member

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    shorting out d1, nothing happens.
     
  12. zone97

    zone97 New Member

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    You mean, how may volts when the motor is connected and when its not? Wanna see the load the motor produces?
     
  13. zone97

    zone97 New Member

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    open v 12.08
    on circuit is 10.95
    on load with motor 9.89
     
  14. duffy

    duffy New Member

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    That's the problem, the power supply jumps up a couple of volts. Now the question is what's the simplest way to fix it. Is than an SPST or DPDT relay or what?
     
  15. zone97

    zone97 New Member

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    It is a SPDT
     
  16. duffy

    duffy New Member

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    Wait - no, I didn't say SHORT it, I said "take D1 out of the circuit "!


    Try it without D1. Leave D2, that's a protection diode.

    Also remember that after trying to run it without D2, shorting out D1, and putting the transistors in backwards, those two poor little three-legged 2N2222 troopers may have gone off to the land of eternal silicon rest and need replacement.
     
    Last edited: Feb 10, 2009
  17. zone97

    zone97 New Member

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    Nah, they still work. I thought you still needed to take the cap to ground. Let me try taking it out completely.
     
  18. duffy

    duffy New Member

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    The cap will still go to ground when the power supply is shut off, it just takes longer.
     
  19. zone97

    zone97 New Member

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    Same. No change. works fine for the 10-15 seconds then chatter. But only when the motor is connected.
     
  20. KMoffett

    KMoffett Well-Known Member

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    duffy,

    One thing What may be the problem is that the output transistor (Q1?) spends a lot of time in the linear region, before the relay trips OFF. And it is still in the linear region even after that. I watched that on the o-scope. With just the relay, it's no big deal. But, when zone added the motor, as the relay tripped OFF and the motor stopped it probably allowed supply voltage to climb, increasing the voltage for the relay, and causing the relay to trip back ON. This restarted the motor, which caused the supply voltage fall, tripping the relay back OFF, stopping the motor, increasing the supply voltage, tripping ON the relay...and on and on and on. That was the chatter on release, Eventually C1 will charge enough to take the transistors into cutoff.

    I think the solution would be a "stiffer" power supply, or a separate supply for the motor, or a switching circuit that is more absolute in transition...think Schmidt trigger.

    Ken
     
    Last edited: Feb 10, 2009
  21. zone97

    zone97 New Member

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    I tried a more robust PS, same result.
     

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