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Blows out the 12V adapter

  • milenyakimov Thursday, May 28, 2015 8:07 PM Reply
    The valve works fine, but just blew out second 12V adapter in 3 weeks.
    First was 12V/2A adapter power supply for IP camera, and it just stopped, then started heating, and when I measured I got 0V on the output.

    Then I put 12V 0.5A from another IP camera adapter, and today when I started the valve, it started for about 1 second and stopped, the adapter is gone again.

    I suppose when I put new power supply it will work again, but it would burn out the power supplies. Do you think, is it measured if there is any high inrush current, like only in the starting phase for the first few seconds to current to be few amperes or something and then eventually to drop to 300mA.

    I am planning to install meanwell power supply with protection now, 3-4A.

    And another question - it says 12V DC, but on the valve I never saw + and - indication. Does it mater +and- and is it really DC or it should be 12V AC

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  • ebpDoug Thursday, May 28, 2015 8:38 PM Reply
    The valve is operated by a solenoid coil, which will be very inductive. The current at the instant the power is connected will be zero and will then rise, probably within several milliseconds, to about 300 mA.

    How are you controlling the power to the valve? Are you switching the 12 volt side or the AC input to the power supply?

    Because the coil is an inductor, it will store energy in a magnetic field. When the power is disconnected, the stored energy has to go somewhere. This can cause a spike of hundreds of volts, depending on the circuit and how fast the power is removed. It is common to use a diode across the coil, connected so that the diode does not conduct with the normal polarity of the applied power (that is, the cathode of the diode would go to the coil terminal that connects to the positive of the power supply). The diode will make a path for the stored energy to discharge through.

    Usually for this kind of valve the polarity does not matter, but you must use DC. If you apply AC the moving core that actually operates the valve will just vibrate.
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    post edited by ebpDoug on 5/29/2015 at 5:53 AM
  • milenyakimov Friday, May 29, 2015 5:22 PM Reply
    Thank you very much! That sounds reasonable explanation

    I used to plug in and out the adapter from the mains 220v.

    So now I am planning to use constant powered psu 220v to 12v and install 10A small relay which will disconnect the Positive of 12v connected to the valve. Do you think I will need the dioide again?
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  • milenyakimov Friday, May 29, 2015 5:34 PM Reply
    Thanks I looked around the protection diode, I will install relay and the diode in parallel to the coil. Sounds really reasonable. Thanks again!
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