Using 12V relay to feed a 16-24V electric door strike

Discussion in 'The Projects Forum' started by johntee, Jul 21, 2009.

  1. johntee

    Thread Starter Member

    Jul 20, 2009
    15
    0
    Hi folks... I hope this isn't too basic a question, but I just realized my little project has a small snag -- two different voltages involved...

    I bought a RFID Access control unit (a keypad-style device where you can swipe an RFID tag near the reader to allow access into the building), and I hoped to run an electric door strike from it. The door strike normally sits in "locked" position, and when juice hits it, it moves a piece of metal out of the way (I assume via magnets) to permit the door's latch to clear the door strike so people can enter.
    I think normally the door strikes would be operated directly by a doorbell transformer, getting the electric only when someone inside pushes the button to "buzz" someone in. Since this is for an unattended building, I needed the Access Control unit to decide when to "push the buzzer", when a proper RFID is presented to it.

    The Access Control unit runs on 12VDC (operating voltage = 12VDC, current = 1.2A), with a Lock Relay of 12VDC/2A, but the electric door strikes said 16-24V.
    What would be the simplest way of allowing the 12V coming out of the access control unit to feed the 16-24V door strike? (I figured maybe a 5-second "buzz" to the strike to allow people time to open the door, if the length of time matters.)

    What would the strike do (anything?) if hit with 12V instead of 16-24V? Would I damage the strike by trying that?

    And one more question -- if the Access Control unit has a 12V/1.2A Operating Voltage, and its Lock Relay is 12V/2A, would my power supply need to be > 3.2A, rather than just 2A? I assume a larger amp supply would be OK too?
    (Now I've really shown my ignorance...) :)

    Thanks for any help or suggestions!
    John
     
  2. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    Which products have you chosen to implement this? If you give a link to the specifications or installation information we may be better able to answer the questions.

    From what I have seen, the lock relay can be powered from the access control unit but another supply is required to power the door strike. The 2A rating on the lock relay may be for the relay contacts, they are capable of conducting 2A, and not for the power to engage the relay.

    In your case, you will definitely need another supply if you are going to stick with a 16-24V model door strike. If you put 12V into the 16-24V model, chances are it will not open. It is most likely another coil that you are driving so it should not get damaged by trying, but it may just not function. There are many 12V electronic door strikes available.
     
  3. johntee

    Thread Starter Member

    Jul 20, 2009
    15
    0
    I don't think the components are a "name-brand" that you'd recognize -- cheap Chinese imports, to judge from price and the pamphlet's somewhat butchered attempts at English. Here's the Access Control Unit and the specs from its pamphlet --

    And here's a pic of the electric door strikes (they were already on an apartment door, so no pamphlets, but they're supposed to be 16-24V).

    (Um, I just wondered -- is it 16-24V AC that the strikes would normally get from a doorbell transformer? Rather than DC?)
     
  4. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    If you look at the door strike in the link it has both AC and DC options so unless you know more about the one that you have you will have to try it to see if it works.

    http://www.nokey.com/electricstrike.html

    After looking at some doorbell transformers and howtos, the transformer voltage does indeed seem to be 16V, I saw one recommendation for 24V for long runs. Definitely worth a try with your door strike if that is the voltage that you think it works at.

    Here is a link to a more easily readable diagram of how the system is connected when the access control unit and the door strike use different voltages.

    http://lib.store.yahoo.net/lib/853111/WireDiagramKP1.pdf
     
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