Solenoid control

Discussion in 'The Projects Forum' started by Xefro, Dec 29, 2014.

  1. Xefro

    Thread Starter New Member

    Dec 17, 2014
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    Hey guys, I have a 12v negative triggered solenoid that I need to power.

    When the solenoid receives the ground signal I need it to go to full voltage for 2 seconds and then drop down to 400hz 60% duty cycle until the ground signal is removed to avoid burning up the solenoid.

    What would be the best way to accomplish this?
     
  2. blocco a spirale

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    Jun 18, 2008
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    Does it have to be a PWM signal or could you just use a series resistor to reduce the current?
     
  3. MikeML

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    Oct 2, 2009
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    Do you mean that you want to apply 12Vdc to the solenoid for the first two seconds, and then reduce the current through the solenoid to 60% of the initial current?

    All you have is one input? What is it? A switch contact to ground?
     
  4. Xefro

    Thread Starter New Member

    Dec 17, 2014
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    Correct on both accounts.
     
  5. MikeML

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    What is the DC resistance of the solenoid?

    I'm guessing less than 10Ω?
     
    Last edited: Dec 29, 2014
  6. Xefro

    Thread Starter New Member

    Dec 17, 2014
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  7. blocco a spirale

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    Where does the 2 seconds come from, is this just an arbitrary figure? e.g could it be 1 second or 0.5 second?
     
  8. MikeML

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    Here is how I would do this:

    The simulated "switch to ground" closes at 0.1s, and opens at 4.1s.

    108.gif

    This shows a close up of the solenoid current during PWM. Note the freq, duty cycle, and average current... I used 6Ω as the solenoid resistance, so the current initially is 2A. 1.27/2 is 63% during PWM.

    108a.gif
     
    Last edited: Dec 29, 2014
  9. blocco a spirale

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    If all you want is to ensure that the solenoid receives full power to fire initially and then reduced power to hold it in place without burning out; you could try fitting an 8 Ohm 10W resistor paralleled with a large >=10,000uF electrolytic capacitor, in series with the solenoid.
     
  10. MikeML

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    It will take a huge capacitor, and then the current profile is still an RC time constant, where it spends very little time near the peak current. Also, R1 has to be a 10W resistor (also huge). 108c.gif
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    This is presumably a AC solenoid? why can't you use a DC solenoid and avoid the burn out problems, an AC solenoid should normally never see a reduced voltage.
    Max.
     
  12. blocco a spirale

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    Jun 18, 2008
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    Yes, I believe I already said the resistor should be rated at 10W, which I would not consider "Huge", Nor would the capacitor be "Huge" due to its low voltage rating.

    It's just a suggestion, something the OP could try if he just wants a simple solution rather than an electronics project.
     
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