A wall-wart alternative

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It will sound, if "the mains fail" for less than 1 year :-)

That's just a line cord cut off a dead appliance, in many cases.
Nick
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Won't fly in Canada. Smokes have to be on their own circuit.
wrote:

wont sound.

year :-)

to the detector

many cases.

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You may find that is untrue, if the AC merely keeps the battery charged.
Nick
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Smokes have to be on their own circuit. Battery operated ones do not pass code.
wrote:

circuit.
the battery charged.

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Are you sure? :-)
http://www.safety-council.org/info/home/smalarm.htm
... Smoke alarms can be electrically powered, battery powered, or a combination of both.
http://www.ibc.ca/homeauto_homeinsure_smokealarm.asp
... You should also test your alarm monthly to make sure it's working. Use a candle, cigarette, or incense to introduce smoke into the alarm until it sounds. If the alarm is battery-powered and doesn't sound, replace the battery and try again. If it's electrically-operated and doesn't sound, check the fuse and try again. In either case, if the alarm still isn't working, replace the unit. A dead unit is worse than none at all, as it can give you a false sense of security.
Saanich BC Smoke Alarm Bylaw No. 7126:
... Smoke alarms installed pursuant to this bylaw may be battery powered or connected to an electrical circuit... Where the owner installs an individually battery powered smoke alarm, the owner shall install new batteries in the alarm at least once every twelve months.
And finally, your Queen :-)
http://www.hc-sc.gc.ca/iyh-vsv/prod/detect_e.html
Smoke Detectors
(c) Her Majesty the Queen in Right of Canada, represented by the Minister of Health, 2004
... Change the batteries as often as recommended by the manufacturer.
Nick
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On 11 Jan 2006 17:11:32 -0500, snipped-for-privacy@ece.villanova.edu wrote:

Nothing I see there refutes the statement that smoke alarms must be on their own circuit... that is, they can't legally be plugged into a random outlet...
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No.I am not sure now....LOL After some research all I can find is in the building code but the 1990 Electrical Code says it' OK to combine smoke alarms on circuits with other devices.
I don't believe battery units are allowed in new construction at all because nobdy ever checks them. They must be wired in.
From our latest Building code:
A-3.2.4.21.(5) Smoke Alarm Installation. The Electrical Code permits a smoke alarm to be installed on most residential circuits that carry lighting outlets and receptacles. It is the intent of this Code that any other item on a circuit with a smoke alarm should be unlikely to be overloaded and trip the breaker with a resultant loss of power that is not sufficiently annoying for the breaker to be restored to the on position. It is considered that an interior bathroom light or a kitchen light fulfills this intent, but that circuits restricted to receptacles do not fulfill this intent.
Not quite what I was thinking but thanx for the red flag.
wrote:

circuit.
powered,
sure it's working. Use

into the alarm until it

sound, replace the

and doesn't sound,

alarm still isn't

none at all, as

be battery powered

owner installs an

shall install new

months.
the manufacturer.

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Alarms that beep when the battery is low are self-checking, if anyone's home and they beep long enough and the occupants don't simply remove the battery to stop the noise, which I seem to have done with my smoke detector a year ago. I just opened it up to check the battery current and... whoa, no battery! :-)
The Canadian UL standard for smoke alarms (ULC S541?) seems to allow a battery with AC backup. (I haven't seen the standard itself, just a summary of it.)

This makes a smoke alarm power failure more apparent than if it were on a dedicated circuit. Failure alarms are good. High availability can come with long-life redundant components AND a way to tell if one has failed so we can repair it before others are likely to fail, keeping the system in working condition during the repair period.
We might compare numerical UNavailabilities in seconds per year for
1. AC only (600?) 2. Battery only (10?), 3. Battery with AC backup (alarm only works if battery works) (2?), and 4. Alarm works if either AC or battery works (1?).
The AC only option may not be as good as it seems based on grid failure stats, since a house fire can cause a loss of house power.
Nick
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wrote:

The schools around here have a fire safety program for the kids every October. So I got in the habit over the years of buying nine new 9V batteries each October and changing the batteries in the smoke detectors (yes, *9* of them).
Just put it on your calender to do this during some season (say superbowl, or halloween, or new-years) and just do it. The batteries I take out still have plenty of life, so I use them for other things. But the smoke detectors is one place I don't skimp.
daestrom
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A bad habit? :-)

You might charge-pump them and merely test yearly by pushing the button...
My clock radio has 3 AAA cells and uses 120 uA for the clock alone, 25 mA with low radio volume, and 50 mA at high volume. At low-volume for 1 hour per day, it needs an average (23hx120ua+1hx25mA)/24h = 1.16 mA = 60x370C, which makes C = 0.052 uF... 0.1 can float the batteries at about 4.5 V without overcharging, like this, viewed in a fixed font like Courier:
0.1 uF @400 V* || 0.6V -----------||--------------------->|------------> || | | | | 4.5V 120 VAC /-/ --- to radio ^ 5.1V _ | | 10K | | -----------www----------------------------------> This can go into the wall-wart that came with the radio, with a wire inside the radio to connect its jack to the batteries.
A similar circuit might keep our church clocks running with power from the seldom-lit exit signs below them. They have a single AA cell.
0.1 uF @400 V* --1.8V-- || -----------||------------------>|->|->|---------> || | | | | 1.5V 120 VAC /-/ --- to clock ^ 3.3V _ | | 10K | | -----------www---------------------------------->
Digikey's 1N5226BDITR-ND 3.3 V zeners cost $13.65/100, Their 586-1361-1-ND switching diodes cost $3.38/100.
Nick
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wrote:

No, I test them monthly, and replace the battery yearly regardless of their state of charge. The batteries get used in other things, but smoke detectors and CO monitors are not the sort of applications I 'experiment' with.
daestrom
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If you and your family are worth $10 million and non-pumped batteries have a 2 year MTTF and pumped batteries have a 10 year MTTF, with a 2 week MTTR for both, (because it takes a month to discover them) and you have a fire every 10 years, does your battery changing save money, on average?
Nick
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snipped-for-privacy@ece.villanova.edu wrote: ...

Nick, you've totally lost me on this one. First off, people aren't worth $10 million. The average cost to an insurer for someones death is in the $50,000 range and certainly children wouldn't be valued as much. Ask any life insurance salesman what kind of policy they would sell for a child. I doubt they would sell many over $10,000. Houses cost more than people today. Replacing a home in Los Angeles could easily cost half a million or more.
Next, I don't understand anything about this MTTF you're tossing around. Replacing the batteries within one year is a safety measure, as is the replacement of the alarms themselves every 10 years. You can run all the theoretical analysis you want on projected failure rates but it's always better to error on the side of caution. I'd rather spend the extra $10 a year on batteries if it means I don't die. It would be a cheap and stupid thing to die because I wanted to save a couple of bucks.
Anthony
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It was a joke, joyce.

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The answer to that question is no, if the pumped batteries have a higher MTTF, which seems reasonable to me, but you might imagine otherwise...

That's part of the picture. People can be worth a lot more than they are typically insured for, if someone with deep pockets is paying. If daestrom were a promising young brain surgeon, we might estimate he would earn $10 million or more over the remainder of his lifetime... $50K/year over 50 years is $2.5 million.

It's more complex, no? For instance, replacing batteries takes time, and you might subtract that time from your lifetime, unless you love that activity, and you might fall off a ladder when replacing a battery or drive into a tree on the way to the battery store, and you might use the money you save by less frequent replacements to armor-plate your SUV or buy safer tires or upgrade the seatbelts, which might be better safety investments.
Nick
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wrote:

Some insurance salespersons will sell you as large a policy as you want, regardless of the logic involved :-( The only difference is the premium you pay.
But an insured policy value is *not* the measure of human life. Especially a close family member. Also, the *costs* of replacing a house go way beyond the $ value.
Smoke detectors, portable fire extinguishers, CO monitors are all just safety devices designed (usually) to help protect one from various hazards.
Replacing batteries in them on a regular basis is similar to fastening your seatbelt or storing gasoline in approved containers or turning off the power before rewiring a wall switch, or.... Sure you can 'get away' with skimping on these sorts of things. There's a simple name for folks that willingly chose to not follow well-founded safety precautions: 'statistic'.
daestrom
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Life insurance - Placing a bet on your life, if you die you win.
Anthony Matonak wrote:

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snipped-for-privacy@ece.villanova.edu wrote:

Now we get to see the results of talking engineeering to people that dont understand it.
NT
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snipped-for-privacy@ece.villanova.edu wrote:

If mains is lost, and battery works, youre right it will sound. If the battery goes down it wont. So you dont get the full reliability benefit of a mains alarm with battery backup.

well, not here. One needs to use 1mm2 3 core cable, and route and wire it in. Which is a good deal more than just grabbing a bit of flex. You may be happy to string a bit of fle across the ceiling, but youre in a minority on that.
NT
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Have you ever disconnected a smoke detector from the mains supply?
I have
Those bastards wail for 20 minutes after disconnection. They are a pain in the butt. I do not understand where they store all that energy after 15 years of usage.
wrote:

wont sound.

year :-)

will sound.

full reliability

to the detector

in many cases.

and route and wire

bit of flex. You

ceiling, but youre in a

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