Question about relays

Discussion in 'The Projects Forum' started by theabsurdman, Oct 4, 2012.

  1. theabsurdman

    Thread Starter New Member

    Oct 4, 2012

    I have an old-fashioned 3v battery doorbell which I wanted to extend wirelessly down to end of my garden so I bought a Friedland wireless extender consisting of a transmitter unit and receiver chime.


    the transmitter has a 1.5 watch battery inside and 2 input wires which when shorted trigger the remote chime. so far so good.

    However when I wire the transmitter into my existing bellpush, the 3v in the circuit stops the transmitter firing.

    I tried isolating the transmitter with a cheap 5v sealed reed relay from maplins:


    which works a treat BUT flattens the battery of the transmitter within a matter of a week, so I guess the "control circuit?" of the relay must be drawing some current all the time.

    does anybody have another solution that will work while preserving the transmitter battery?

  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    A relay will kill a battery in no time.

    OK, so this transmitter has two lines, short them and it gives out the signal to the remote. Does that much work well and for a long time?

    Does the existing bell push connect to anything else or is it just a normally open momentary push button? That's what you want to make this work. If you have another system wired to the button that is probably what is killing things.
  3. theabsurdman

    Thread Starter New Member

    Oct 4, 2012
    thanks for replying,

    yes, the push button is wired into the old 3V battery bell circuit because i want to keep the original bell as well as trigger the new wireless one.

    i want the push button to simply short the transmitter wires a/ without passing 3v to the transmitter and b/ without drawing any current whatsoever from the transmitter battery.

    would an electromechanical relay work better than the reed switch?
  4. cork_ie


    Oct 8, 2011
    3V electromechanical relays exist but I would be surprised if they were readily available.
    I don't quite understand why the relay or reed switch should drain your battery, as the coil would be powered from the 3V in your original bell.
    If it were my bell I would try and find a double pole momentary push switch and bury it behind your existing bell button.

    One other thing to consider is that a lot of bell pushes have a light built in , this bulb is in parallel with the normally open contacts and there will be a permanent drain through the bulb.
    Last edited: Oct 4, 2012
  5. theabsurdman

    Thread Starter New Member

    Oct 4, 2012
    that sounds like a plan. the bell button is old and decorative and i'd like to keep it, if possible.

    thanks again