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Door bell problem

Discussion in 'Electronic Basics' started by Brent, Jan 3, 2004.

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  1. Brent

    Brent Guest

    I posted about this in the thread "Need to mod door bell" on 12/20/03
    and was given several things to do. But I'm having trouble deciding
    which to do.
    I was also asked to post more info or a schematic, which I did on
    12/30 but didn't get any replies.

    My problem:

    While I was gone one day, my door bell button got stuck and since the
    'ding' piston in the bell unit was stuck out (w/ current), it melted
    the the plastic around it, so it doesn't work.
    I just replaced the button < 2 years ago, with Broan button with nice
    brass plate (not the cheapest they had). Yes, I can/will get another
    button, but there's always a possibility it could happen again. It
    seems like it could be a fire hazard too.

    What the best or easiest mod can I do to keep the bell from melting
    again if the button sticks?

    transformer and wall box:

    door bell unit:


    simple schematic I drew:
    Sorry I couldnt get the text tool to work to label. Blue box is the
    wall box (wires go to circuit breaker panel/door bell button), black
    filled box is the transformer, black outlined box is the door bell
    unit, gold wire is bare copper wire, light blue thing is where i
    thought about adding a fuse.
  2. happyhobit

    happyhobit Guest

    Hi Brent,

    Your schematic don't look right. You should have two wires from your
    doorbell. (Your drawing only shows one)

    One wire from the doorbell goes to the transformer secondary (screw
    terminal) and the other wire goes to one of the pushbutton screw terminals.
    A wire from the other pushbutton screw terminal goes to the other
    transformer secondary terminal (screw terminal). The transformer primary
    (120 VAC) looks correct.

    I did a Google for "Doorbell circuit" and got,, and 128 others.

    The secondary is not usually fused but it wouldn't hurt. If the secondary
    was fused the fuse probably wouldn't have blown. You would probably smell
    the plastic melting first. I doubt that there is a big danger of fire.

  3. Neil

    Neil Guest

    I disagree, I think that putting a low-amperage (try 500ma or 1 amp max
    fuse) in series with the output of the transformer. If anything shorts, it
    will probably blow the fuse before anything melts.
    Try experimenting with different values of low amperage fuses, if you don't
    know how to measure amperage.

  4. Bill Bowden

    Bill Bowden Guest

    Well, you might add a resistor and LED light across the
    button which will light when the button is open.
    So, when you notice the light is out, it means the
    button is stuck.

    Another idea is to use a small relay across the button
    so the relay opens when the button is pushed. The relay
    could control a timer that shuts off power after some
    period of time.

  5. happyhobit

    happyhobit Guest

    Hi Kim,

    If you're disagreeing with, 'If the secondary was fused the fuse probably
    wouldn't have blown.' Then I'd point out that the pull in current for the
    bell is higher than the maintaining current. So it won't blow if the
    pushbutton sticks.

    If it's the, 'I doubt that there is a big danger of fire.' Then I'd point
    out that if there was a 'big danger' then someone would have come up with a
    good solution it before now, maybe like making the coil with a fire
    resistant plastic.

    Adding a fuse won't hurt I just question the benefit.

  6. Brent

    Brent Guest

    Maybe the problem is that the one white 'wire' I show by itself on the
    right side is actually two conductor wire. I drew it just like it is
    to match the photos (did you look at them?). In the drawing you can
    see where the outer sheilding ends and it 'splits' to two separate
    conductors. One goes straight to bell, the other to the transformer
    (then to the bell), just like the howstuffworks page.
    Again, sorry I didnt label the items. Makes it harder to figure out
    my drawing. I had to hurry and couldnt get PSP's text tool to work
    (but have several times before). I may go back and try again.

    Mine is wired like those in the links you gave, but I dont think those
    or mine is wired like you describe. But it's late. I'll have to think
    about it later.
  7. happyhobit

    happyhobit Guest

    I'm sorry Brent,

    I did look at the photos but failed to see the two wires coming from the
    twin-lead, my error

    Selecting another color in your drawing for the twin-lead (gray or off
    white) would make it easier to understand.

    Now that I understand, your wiring looks correct and your proposed location
    for the fuse should be fine.

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