Wired Smoke alarms power usage

eusap

What kind of power usage should a wired smoke alarm use? I changed three of mine yesterday to nest and the power usage went from 75w to 15w, if they were using 75w it accounts for around 18€ per month of cost or am i confused

kirving

Were they previously using some enormous transformer to step down to 12V or something?

kirk.

Not familiar with Nest but usage should be minimal with alarms- like you don't notice on your bill usage

Did you change from wired to wireless

cml387

There's absolutely no way that a smoke alarm will consume 75W. Maybe 0.75W

10-10-20

https://www.boards.ie/discussion/comment/120450986#Comment_120450986

Agreed. These are low power devices. Even 15W sounds high as I would expect around 1W each. What brand were the old units?

kirk.

https://www.boards.ie/discussion/comment/120451030#Comment_120451030

What's the usual for these devices

You hear a lot of stories about vampire power and insane usage

L1011

edit: misread the post and thought it was saying the Nests were the high consumer

Wired smoke alarms are the same tech inside them as battery powered ones that can do years on a single 9v zinc carbon battery - if they were pulling 15w each it has to have been going out as heat from a crap transformer inside them surely.

Nests will use more power than normal alarms as there's a lot more in them, and even then the battery versions use in the milliwatt range over their duty cycle - years on 4x1.5v Lithium AAAs.

10-10-20

https://www.boards.ie/discussion/comment/120451115#Comment_120451115

EI state most of theirs to be 0.75W.

Dave Jones covers it off well in his EEVBlog, it's down to bad power-supply design (still using bridge-rectifiers) giving bad pF:

https://youtu.be/_kI8ySvNPdQ?t=199

L1011

Didn't even think of power factor; that could be having a significant impact. Would need to know what the OP is using to measure consumption but a lot of consumer kit will measure apparent power I think? Pointlessly as that's not what consumers are charged on.

eusap

https://www.boards.ie/discussion/comment/120451196#Comment_120451196

I have a effergy monitor and took a reading before disconnecting and after connection, the Nest are wired versions

L1011

https://www.boards.ie/discussion/comment/120451629#Comment_120451629

I would assume Effergy kit measures actual not apparent power, seems to suggest so anyway.

Bruthal.

https://www.boards.ie/discussion/comment/120451196#Comment_120451196

They measure current, with voltage based on a fixed selection by the user, so they measure an estimated kva/va/apparent power. Domestic premises are not charged for wattless units, although with smart meters now, it could be done. A nice possible stealth increase that could be, if there was many wattless units being used.

kirk.

https://www.boards.ie/discussion/comment/120451152#Comment_120451152

What would be be the usual background usage over 24 hrs

modems TVs on standby and the like

Would it be a kilowatt

pron

https://www.boards.ie/discussion/comment/120455669#Comment_120455669

Base use (loads of stuff on standby + fridge / freezer etc) in our household (6 people) is around 200W, which will include some (LED) lights etc according to the Zappi. So the thick end of 5kWh / day base load

L1011

Mine is ~250W according to the now available smart meter stats without a smart meter plan

That would be fridge, routers, NAS, various alarms (house, smoke, heat, monoxide), zigbee hub, nest, background charging of other kit.

Awaiting availability for the second house which just has fridge, zigbee, nest and a router. Wouldn't be surprised if my huge but newer fridge is better than the smaller but old kit there. Battery alarms and way less kit there.

Rows Grower

https://www.boards.ie/discussion/comment/120455918#Comment_120455918

Your huge new fridge will probably need more energy than your old smaller one, the most energy efficient ones are 16-20 cubic feet.

RainInSummer

https://www.boards.ie/discussion/comment/120451140#Comment_120451140

That's 6 X AA. But yeah. They don't pull much at all. I swap out the batteries every 3 years or so. I'd guess whatever meter is being used to measure their usage isn't accurate at low levels.

eusap

The effergy energy meter averages around 350w for fridge, routers, NAS, various alarms (house, smoke, heat, monoxide), hue hub, Google speakers x3, mesh wifi x 4, cctv cameras/dvr, trying to get it as low as possible with essentials still on

kirk.

I thought monitoring every circuit was way overkill but it would come handy there on 2 threads

The random rcd trip you might be able to narrow down what was in use if anything

Also getting a huge electric bill should narrow down the problem there