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Clipsal smoke alarms

Discussion in 'Hobby Electronics' started by Suzy, Oct 17, 2007.

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  1. Suzy

    Suzy Guest

    We have one -- the normal type that have a 9v battery and fit to the
    ceiling. It started beeping intermittently (and loudly) so investigated.
    "Old" battery showed 9.4 v dropping to 8.9 v when loaded with 750K (giving
    approx 20 mA load - probably much too high). Replaced battery with new
    Duracell which gave 9.7 v dropping to 9.6 on load. No beeps now. I wouldn't
    have thought the inbuilt low battery alarm was so sensitive. Any comments?
  2. You mean 750R, not 750K, right?
    Dead ones I've pulled out of my smoke alarms were (from memory) below
    8V with no load. 8.9V under load means that battery has plenty of
    juice left. Something is fishy...

  3. Doug Jewell

    Doug Jewell Guest

    750k at 9V is a 12uA load not 20mA. For a 20mA load at 9V you would need a
    450ohm resistor.
    If the battery is dropping from 9.4v to 8.9v on a 12uA load then it is
    pretty flat.
  4. Suzy

    Suzy Guest

    Yeah, I meant that, Dave!
    Yeah, I would have thought that!
  5. Suzy

    Suzy Guest

    Agreed. I meant 750R of course!
  6. **I decided to fit some mains powered smoke alarms in my last home. I chose
    some fairly expensive ones, which had a battery back up. After climbing
    ladders to get into the ceiling space at 2AM to disconnect the power
    (twice), I decided to switch to another brand. I spoke to the guy at the
    electrical wholesale outlet (Turks) and asked which model was the most
    reliable. I've been happy and false alarm free for several years.

    Go ask the guy at the electrical wholesale outlet nearest you. They know
    which models are the least troublesome. Buying smoke alarms from K-Mart (or
    other, similar outlets) is the worst place to buy them.

    BTW: Photo-electric is generally regarded as best for normal situations.
    They're usually more expensive.

    Trevor Wilson
  7. Suzy

    Suzy Guest

    Yes, that was our problem but fortunately, I can swing down the unit from
    within the house, which disconnects if (the unit) from the mains, and then
    on removing the battery there are just a few shrieks as the capacitor
    discharges, and then peace.

    There's nothing quite so disruptive at 2 am than a beeping smoke alarm
    (except possibly a smokelogged house -- hence I don't want to disable it).
    Does seem however that some models are unduly sensitive to very small
    battery ageing.

    All Ok now with new Duracell.
  8. Franc Zabkar

    Franc Zabkar Guest

    Assuming you mean 750 ohms, then I've had similar experiences with
    various smoke alarms. However, instead of discarding my "flat"
    batteries, I've used them in my multimeter.

    - Franc Zabkar
  9. Suzy

    Suzy Guest

    Yes, 750 ohms of course!
  10. kreed

    kreed Guest

    Being environmentally responsible, and a lot more pleasant than eating
    your own ear wax like some ;)
  11. Franc Zabkar

    Franc Zabkar Guest

    I just had an Eveready "Super Heavy Duty" battery go flat in a $5
    smoke alarm. It measured 7.7V on no load and it overranged (> 100
    ohms) on Bob Parker's ESR meter.

    - Franc Zabkar
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