Clipsal smoke alarms

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.

Yeah, I meant that, Dave!

Yeah, I would have thought that!

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.

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.

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

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



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