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Thread: Door strike

  1. #1
    Join Date
    Sep 2003
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    Rochester, MN
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    Door strike

    I have a project that has a 24vdc door strike controlled by 2 locations. 1 is a standard push button and the other is a thumb print reader with dry contacts. Wiring and polarity all appear to be correct as well.
    Every 4-6 uses, the strike will fail to open the door, and a little while later it starts working again.
    We have replaced every component with no success. The wire tests free of shorts or ground faults.

    It acts like a thermal that kicks out, and then automatically resets, but the voltage at the dc power supply maintains a steady 24.5 volts.

    Any thoughts?

    Bob
    Bob

  2. #2
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    What's the reading at the device and again under load?

  3. #3
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    Sep 2014
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    Nashville, TN
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    If the lockset is a knoblock, the auxilary bolt (in red below) could be dropping into the strike when the door closes too hard. If it's a metal frame, check the silencers (on right below) in the frame. They may have been painted, they may be old and hard or they may be missing.
    Click image for larger version. 

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    The door needs to close firmly but not slam (a function of the door closer and its adjustment). If the door is warped, the end user needs to fix/replace it. There will be times when the door will slam and there is nothing that can be done about it. I saw a hinged door replaced with a slider because of the few days a year when the wind was just right (or wrong) and the door slammed.
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  4. #4
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    Quote Originally Posted by sameguy View Post
    What's the reading at the device and again under load?
    At the power supply it is 24.5 volts. When the strike is activated, it goes down to 23.5 volts. When it is not working, the power supply stays at 24.5

    The electric strike is new, on a new door. No binding or anything else was noticed.

    Bob
    Bob

  5. #5
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    Does this happen with just the thumb reader, just the PB, or both?

    Also, is anything controlling the length of time the strike is energized? If this one is intermittent duty and is being energized for too long or to often, it can overheat.

  6. #6
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    Quote Originally Posted by zbang View Post
    Does this happen with just the thumb reader, just the PB, or both?

    Also, is anything controlling the length of time the strike is energized? If this one is intermittent duty and is being energized for too long or to often, it can overheat.
    It happens with both. The thumb reader is set for just a few seconds and the push button is only pushed for a second or two also.

    I will check to see if it is intermittent duty. That would make sense.
    Bob

  7. #7
    Join Date
    Sep 2014
    Location
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    Give the door a push with your shoulder to see if you can recreate the problem "on demand". If this is a new building, the HVAC people probably haven't balanced their system. See if "Push before pull" works.

  8. #8
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    Quote Originally Posted by dnbob View Post
    At the power supply it is 24.5 volts. When the strike is activated, it goes down to 23.5 volts. When it is not working, the power supply stays at 24.5

    The electric strike is new, on a new door. No binding or anything else was noticed.

    Bob
    If you are reading those voltages at the strike, they indicate that there is no current flow though the strike coil when it is not functioning.
    Don, Illinois
    (All code citations are 2017 unless otherwise noted)

  9. #9
    Join Date
    Apr 2008
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    Ann Arbor, Michigan
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    180914-2410 EDT

    I believe dnbob is saying that at his 24 V source the voltage is 24.5 V with no load. When the striker works the source voltage drops to 23.5 V during activation. Obviously meaning load current is flowing.

    But when the striker should operate and does not, then the source voltage remains at 24.5 V meaning that no current flows.

    The obvious thing to do is measure the voltage at the striker. Voltage should only appear here when the striker is to operate. If the 24.5 V appears and the striker does not operate, then there is a striker problem. If no voltage appears, then obviously the problem is in the wiring or the devices containing the switching contacts. Note, the controlling contacts are normally open and in parallel (a logic OR circuit). Not likely the contacts.

    .

  10. #10
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    If you remove the strike and hold it in your hand does it still exhibit the same problem?

    If not there is a mechanical problem with the door somewhere.

    If it does check for voltage at the strike.

    I assume that you are using a DC strike of the correct voltage.

    -Hal

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