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?
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...Dave.
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.
Yeah, I meant that, Dave!
Yeah, I would have thought that!
Agreed. I meant 750R of course!
**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
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.
On Wed, 17 Oct 2007 17:22:52 +1000, "Suzy" put finger to keyboard and composed:
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
-- Please remove one 'i' from my address when replying by email.
Yes, 750 ohms of course!
Being environmentally responsible, and a lot more pleasant than eating your own ear wax like some ;)
On Mon, 22 Oct 2007 16:21:21 +1000, Franc Zabkar put finger to keyboard and composed:
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
-- Please remove one 'i' from my address when replying by email.
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