Wikipedia:Reference desk/Archives/Computing/2022 May 25

= May 25 =

Household power use
Multiple TV programmes in the UK have said that leaving things plugged in in wall sockets uses a lot of power, even when they're switched off. I one today that said a phone charger uses £1.50 if the phone is never connected to it, a microwave uses £16 if it's never use a TV uses £20 if it's just on standby, and a laptop charger uses £60 if the laptop is never connected. My mum has been saying this for years but I've never believed it.

The phone cable is literally just a metre of wire, without and current being drawn, so it's not clear why that uses electricity at all as no power needs to go on it. The microwave is just an LED display for the clock, which should use no power as you can get an LED clock to run on a 9V battery for less than a year. The TV is just an LED light to say it's on standby. And the laptop admittedly has the transformer, but it doesn't need to be transforming anything if it's never plugged into a laptop. I've never believed my mum or the clips she shares of reputable TV programmes constantly repeating that these things really do use a lot of power.

The question is, why do they use so much power when, in the case of the phone charger, all it is is a little wire, and in the case of other things, all it is is an LED. I just don't understand?? It seems weird that we had to switch things off at the mains and that's better than just switching off or unplugging the devices. 2A00:23C8:4384:FB01:F997:2CDA:CD0E:2582 (talk) 15:29, 25 May 2022 (UTC)


 * Your phone charger will also contain a transformer. What does the other end of the little wire plug into? The TV will have an internal transformer. Microwaves also need to do amusingly massive voltage changes (up rather than down). The question is whether all these idle transformers are using power (and producing a bit of heat from it) or not. Card Zero  (talk) 15:46, 25 May 2022 (UTC)
 * Even if there is no load connected to the secondary circuit of a transformer, there are energy losses; see the section . --Lambiam 16:18, 25 May 2022 (UTC)


 * Thank you both. It amazes me that the average house is wasting hundreds of pounds per year in electricity, as the economic and ecological cost on an individual and society-level basis is massive. I don't know a lot about electricity so I just assumed that they would have figured out how to get transformers to switch off when they're useless. Now I know!! 2A00:23C8:4384:FB01:75B9:9E61:A6F9:25CE (talk) 16:44, 25 May 2022 (UTC)


 * Most modern DC power supplies do not use transformers - they use a Switched-mode power supply. This has almost zero power consumption when it is not actually charging.  It's quite simple to check this with a power consumption meter.  So all the reports of massive costs with leaving "vampire" devices plugged in are nonsense.  Consider the power supply question - if they were consuming electricity, that would have to go somewhere.  And the only possible thing it can do is heat the device up.  Do they get warm?  Nope.  So they're not consuming significant power.--Phil Holmes (talk) 07:32, 26 May 2022 (UTC)


 * Multiple TV programmes in the UK have said that leaving things plugged in in wall sockets uses a lot of power, even when they're switched off. Yes, many programs have made such claims. The BBC reported the same quite recently. Well, the BBC repeated claims made by British Gas. Let's see if it bears up to evidence. The British Gas report says TVs on standby are a big offender. The relevant EU regulation, adopted into British law (and still in effect after Brexit) is No 642/2009, which says "From August 2011 ... The power consumption of televisions in any condition providing only information or status display, or providing only a combination of reactivation function and information or status display, shall not exceed 1,00 Watt." (note that means 1W, not 100W). My 2017-ish LG TV actually consumes less than 0.2W on standby. So what do British Gas claim a TV uses - per the BBC, they say "a TV clocks up £24.61 per year". What does my TV actually cost? Leaving my TV on standby for an hour consumes 0.2Wh. There's 24 hours a day, 365.24 days a year, so (0.2 * 24 * 365.24) my TV on standby consumer 1.753 kWh. How much is that costing me? Per Ofgen, the capped rate for electricity is currently "£0.28 per kWh" (remember 1kWh is 1000Wh). So multiply that and we get ... 49p. Per year. Wow. So not even the true benchmark of prices in the UK, a Caramac bar.
 * My TV is unexceptional; I'd guess it's about average in age, size, and quality. You can check your own usage (search shops for "plug-in meter" - they cost about £15 (about 25 Caramac bars)).
 * So, British Gas is claiming my TV costs 50 times more to keep on standby than it really does. Why would it do that? A cynic might argue that energy companies might be motivated to change the narrative on energy bills, even toward very minor contributors. -- Finlay McWalter··–·Talk 17:50, 25 May 2022 (UTC)
 * Thank you. I've seen it on BBC, ITV, Channel 4, and Channel 5. They've been saying it for years but now energy rates are so high, it's back on the agenda. I don't yet pay energy bills so I don't know what they cost but those numbers sounds just so high to me. I might just buy an energy meter, as you suggest, and see what it says! 2A00:23C8:4384:FB01:75B9:9E61:A6F9:25CE (talk) 18:24, 25 May 2022 (UTC)
 * Our Standby power article may be of interest. CodeTalker (talk) 05:52, 26 May 2022 (UTC)
 * Let's keep in mind that during the heating season (only), this wasted warmth can be subtracted from the household heating burden, although if you have a form of heating that costs less than 100% efficient electric heating, this economic benefit will be reduced. But that 49p a year might in practice only mean about 35p!!!!  (But if you use air conditioning, my point completely fails....)  Hayttom (talk) 16:28, 26 May 2022 (UTC)
 * There is a device in the U.S. called Kill-a-Watt that you plug into the wall and then plug your device (charger, tv, etc...) into it. The device tells you how much power is used over time. I used one a very long time ago to discover that my Westinghouse TV pulled the exact amount of power when turned off as turned on. So, I put it on a switched outlet so I could truly turn it off. I've used it for many other things, but the rule is rather simple. Unplug stuff if you don't need it. If you have switched outlets, use them and turn off the switch when not in use. 97.82.165.112 (talk) 19:17, 26 May 2022 (UTC)
 * For "rule", see social pressure and cargo cult. Card Zero  (talk) 12:02, 27 May 2022 (UTC)

Yes, a power meter (Kill-a-watt here in the US, but that might not work for UK mains voltage) is worth buying. The rule of thumb here used to be that 1 watt of steady consumption costs $1 a year. I can believe that an idle laptop charger could use a few watts, but it would be nowhere near 60 watts. Phone chargers might be in the 1 watt range though I think manufacturers have been making some effort to keep it lower. Phones, on the other hand, keep consuming more and more power. 2601:648:8202:350:0:0:0:738F (talk) 21:36, 26 May 2022 (UTC)

Switchmode power supplies (and older conventional transformers) do leak a little power even when not under load, but it's barely noticeable. Rule of thumb, if a wall wart isn't warm to the touch it's consuming less than 2 watts. Some older devices, such as CRT monitors and televisions, did have substantial standby power draws, but anything relatively modern should not. (CRTs were the big offender, the fast start circuitry in them tended to draw a lot of power, especially as they aged.) 108.54.196.111 (talk) 08:59, 29 May 2022 (UTC)