How to be warned when the AC mains power fails

Discussion in 'General Electronics Chat' started by Jessamine, Oct 6, 2010.

  1. Jessamine

    Thread Starter New Member

    Oct 6, 2010
    I have an ongoing problem where in very damp conditions the RCD trips in my consumer unit. I am dealing with this problem as it is the root cause.

    However after the power has failed my intruder alarm goes onto battery backup which after an hour or two fails and the alarm goes off. Usually occurring about 04:00
    Ideally I would like a light and an audible warning of power failure. A real bonus would be an sms to my mobile phone (cell phone). That is cake icing though.

    I have limited knowledge on circuitry but while thinking about the problem came up with the following idea...

    Plug in an old mobile phone transformer to get a low voltage power supply (I do not like using 240V AC) I have loads of Nokia transformers sitting in a drawer)

    Use the power from the transformer to light a low powered lamp to show circuit is live and run through a solenoid. When the AC power fails so will the power in the mobile phone transformer and so the solenoid closes. This then closes a circuit to a battery powered lamp and a bell to wake me up. Then by a magic box this sends an sms to my phone so if I am not in my bed I can rush home and deal with the problem on the consumer unit.

    Any more elegant ideas or suggestions on how to get this working would be very well received.
  2. eblc1388

    AAC Fanatic!

    Nov 28, 2008
    This does not sound right as the alarm system should have a backup time of some 8 hours or longer after AC fails.

    When was the 12V battery replaced? The Gel type 12V battery goes bad after a few years in use and the symptoms is lost of capacity.

    As a result I have had the Alarm Company replace the battery in my alarm system every 3 year just to avoid the setting off of alarm should the AC fails for a few hours.
  3. tom66

    Senior Member

    May 9, 2009
  4. DigitalReaper


    Aug 7, 2010
    Instead of SMS, you could hook up an old serial modem to a microcontroller and have it call you and then hang up after 5-10 secs.