Alarm System Relay Wiring

Discussion in 'General Electronics Chat' started by TRCarbone, Jul 6, 2012.

  1. TRCarbone

    Thread Starter New Member

    Jul 6, 2012
    I have an alarm system that currently uses a DPDT relay module on each zone. The zone loop is normally closed, and opens when the zone is triggered.

    One side of the relay then controls the input to the alarm system, and the other I use for a home-built automation system.

    The relay modules are Altronix RB5s.

    Here is the issue:

    The coil voltage is run through the zone loop, so the coil is normally energized continuously. When the zone opens, the relay triggers as the coil loses voltage.

    If the power fails, a battery backup takes over, but if that battery drains, the coils all open triggering the alarm.

    What I would like is for the coil to be normally de-energized, and energize when the zone loop opens.

    Since I have 13 zones to modify, I would like the simplest approach to this. Can anyone suggest a wiring modification to make this work?
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    So if you change it then now when the power fails and the battery drains again and someone breaks in there is NO alarm.. Not a situation I'd want..

    What powers the alarm horn when power is lost and battery is drained??
  3. BillB3857

    AAC Fanatic!

    Feb 28, 2009
    Since you have a series loop at present, to convert so that when a zone triggers the relay will energize will require a major modification. Each sensor will need to be changed from a normally closed to a normally open sensor AND each sensor will require two wires going back to the relay/power source. Maybe someone else has a different solution.

    Have you thought of just using a higher capacity battery or adding a disconnect feature that will sense the battery and disable the system when the battery goes below a given level?
  4. TRCarbone

    Thread Starter New Member

    Jul 6, 2012
    There is a separate battery and charging system for the panel and for the relays. Right now if the poer goes out, the relay battery drains dead before the panel, so the alarm goes off when all the relays open.

    I was thinking if the relays are normally unpowere (coil not energized) there is virtually no drain on the battery and it should last a lot longer than the panel.

    Once the panel battery drains the relays are useless anyway.
  5. strantor

    AAC Fanatic!

    Oct 3, 2010
    You might want to consult a fire systems expert as I'm almost certain this falls under some building code. These systems are engineered to fail safe, and you're trying to reengineer it to fail unsafe. I know you justify that with ("Once the panel battery drains the relays are useless anyway"), but I doubt that an inspector would agree with you, and should there be an incident and investigation uncovers that you had tampered with the fire system, you could likely be held criminally responsible. That, and as Bill mentioned, it will require a bunch of new wires ran.
  6. TRCarbone

    Thread Starter New Member

    Jul 6, 2012
    All good points, and you guys have me rethinking this.

    Right now, the relays are Altronix RB5s and the coil draws 120ma. They have another relay, the RBSN, that draws 15ma. That would extend the battery life 8x.

    I may go this route.