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Need help finding power source for solenoid

Discussion in 'Power Electronics' started by TLinaris, Jan 17, 2019.

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  1. TLinaris


    Jan 17, 2019
    I'm a beginner electronic hobbyist and I'm attempting to automate the lock on my door with a 12v 400 ma push pull solenoid. I've got the whole circuit pretty much up and running, using an Arduino to control a relay that cuts on and off power from a wall power supply to the push pull solenoid. Heres my problem, all the power supplies I've ordered, even if they say 12v 400ma, cause the solenoid to become extremely hot after a few minutes and I'm not exactly trying to burn down my house. Obviously in this case the power supply outputs something different then what its rated for, but I've already bought two (the first time I forgot to check the amperage rating before I bought it so that was my fault) and I don't wanna throw too much money into this. I was considering ordering a custom nicd battery instead but thats out of the question due to some battery shipping laws that require signature, and id rather go the plug in to the wall route anyway. If anyone could maybe send a link to a more competent power supply or if anyone has any other ideas, that would be extremely helpful, thank you.
  2. BobK


    Jan 5, 2010
    Can you link to the solenoid? Push- pull indicates to me that one pulse pulls it in and the next one releases it. It sounds like you are powering it continuously, which might not be allowed and explains why it would overheat.

    Cannonball likes this.
  3. TLinaris


    Jan 17, 2019
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    I would advise you to look for an electronic strike plate. These are designed for this application. That solenoid may not be designed for continuous operation.
    hevans1944 and davenn like this.
  5. BobK


    Jan 5, 2010
    No info about duty cycle.

  6. Alec_t


    Jul 7, 2015
    That would be my guess, too.
    How you get that particular solenoid to push (other than relying on the spring return)? Looks to me like it's pull only, misleadingly described as push-pull.
  7. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    Sounds like what you really need is an electric strike lock mounted in the door frame. Below is an image of a typical one offered on Amazon for about twenty-four bux. A momentary pulse of 24 VDC releases the striker plate and allows the door to be pushed open:[​IMG]
    davenn likes this.
  8. davenn

    davenn Moderator

    Sep 5, 2009

    I'm not surprised!

    @(*steve*) and @hevans1944 have given you the correct info

    To use anything else would be unwise
  9. Sid723


    Jan 28, 2010
    "I've got the whole circuit pretty much up and running, using an Arduino to control a relay that cuts on and off power from a wall power supply......... the solenoid to become extremely hot after a few minutes....."

    Sounds like the only problem is the solenoid getting kinda toasty. Not a problem. Instead of having a relay turn on the solenoid, use a TIP120 transistor driver along with a diode (1N2002 or equivalent) across the relay to prevent the transistor from getting hit with reverse voltages. Once you have that working, use an analog output from the Arduino to drive the TIP120 on/off. As you may or may not know, the Arduino does not have a true analog output. Instead it sends a Pulse-Width Modification (PWM) signal to the output instead. A higher analog value out will send a square wave (5v to 0v) with most of the time at the 5 volt level. So, sending a 255 to the output would send a mostly high (5v) signal to the output and sending a 127 to the output would give you a pulsed signal with about 50 percent duty cycle. A zero sent to the output would of course give you zero volts.

    To drive the solenoid on, use an analog output of 255, then after about 100 milliseconds (or so, maybe as much as 500 ms), send a lower value (maybe 127 value) to the same output. The idea is to send just enough of a signal to 'hold' the solenoid in the locked-in position. You may need to test out different output numbers to find just the right 'hold' value. So, your code would have to send an analog value of 255 to the output, wait 100ms, then send a value of 127 to the same output. The 255 value will give the solenoid the full current to move the solenoid to the fully retracted position. The lower value (127) would allow just enough current to flow through the solenoid to keep it at the fully retracted position and not allow the spring to move the solenoid back out (or become toasted). By the way, this is how a modern day pin-ball game flipper works.

    Let me know if that works for you.
    73's de Edd likes this.
  10. Tha fios agaibh

    Tha fios agaibh

    Aug 11, 2014
    I agree that a striker plate is the better/safer way to go but if your load is 400ma, then you should order a ps larger than that. A little headroom is advised.
    I'd go with at least 500ma.
    (*steve*) likes this.
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