more energy to switch something on and off than off totally.

[Andy Hamilton]

Can anyone help settle an argument. I know that it uses less power to switch off a computer totally for about 16 seconds and then turn it on again than to leave it on for over 16 seconds. Is this true for all electrical items?

I suspect it is but am struggling to find any data.

So in plain english does it use more electricity to switch off and then power up an electrical item than to switch it off totally. What is the time span needed when we switch something off. This is a bit of an argument I always encounter and it infuriates me, but am I in the wrong. I always think that we should just switch things off.

[Milims]

It kind of depends. Something like a low wattage light bulb pulls a lot of electricity initially to get it "fired up" but once reaches that stage the power needed drops to more of a maintenance level. If you were to switch it off and straight on again, before the power dicipates from the capacitor then you don't need the big surge to fire it up again. However if you wait a while you do need the surge. A good example is a street light - when it's red it's drawing lots of power, but once it goes yellow it drops and levels out. TV's also pull lots of power to start with - hence the need for a 13 amp fuse for something that only pulls about 5 amps - the initial surge has to be accommodated.

[Martin]

it's an incredibly complex area - basically, when you first switch on something electrical there's a "current surge" - because the device isn't at operating temperature, "cold" it will momentarily draw more current than when it's up and running, because the electrical resistance varies with temperature. Some things like electric motors draw enormous surge currents when starting (sometimes three times normal current draw)........SO, often things electrical "conk out" when being started up (old-fashioned tungsten light bulbs were particularly prone).........
40 or more years ago, it was recommended to leave tvs ON for the evening, as switching it off a for less than an hour and then back on was more likely to result in a hefty repair bill as components "fried" with monotonous regularity on startup, hence it was deemed "cheaper" to burn the electricity
Things are far more reliable these days, but it is still a consideration.......
Even with modern reliability, I'd tend to leave things switched on if I'm going to switch them back on a few minutes later
(working on the assumption that a little extra electricity spent running the thing is cheaper for me, and ultimately the planet than having to repair/replace the thing, especially as many things are not designed to be repaired these days....)

[The Riff-Raff Element]

Like the previous replies, it does depend. Something with a motor (washing machine, pumps, that sort of thing) will usually take a big surge of current on start up to charge a capacitor to provide the initial push to overcome the inertia of the moving parts and get it turning. But this only lasts a fraction of a second, so in the overall consumption it hardly counts.

Something big and electronic - TV, this computer, a stereo, lo-energy lighting - builds up a big charge a bit like a resevoir, but then (comparitively) consumes a trickle. Then the start-up usage is significant.

There was a documentry on French TV about just this topic about, oh, two months ago. The other point they highlighted was the percentages stuff uses when on standby. I can't remember the exact figures, but order of magnitude it was TV and computers about 30%, dishwashers and washing machines in excess of 50%. The latter really surprised me.

The other villan of the peace they mentioned was the broadband internet router box thingy. Left on 24/7 these consume, it was said, hundreds of kwh. The probelm is for most people that the telephone now comes through these, but I've started turning ours off at night.

[marshlander]

We switch off as much as possible at the wall, especially at night- makes sense, every little helps but I can't see that a tiny power on light on the dishwasher can use anything like the power used when working pumps and heaters for the water

[The Riff-Raff Element]

We switch off as much as possible at the wall, especially at night- makes sense, every little helps but I can't see that a tiny power on light on the dishwasher can use anything like the power used when working pumps and heaters for the water

I know - it sounds odd, but the program was a respected current affairs one. How can appliances "leak" so much energy? I was going to look it up on the old interweb but (like hald a million other things I was going to look up) I never did.

[Millymollymandy]

I don't understandhow you can leave a dishwasher or washing machine on standby. There's isn't such a thing on any I have ever known! They are either on or off!

[The Riff-Raff Element]

I don't understandhow you can leave a dishwasher or washing machine on standby. There's isn't such a thing on any I have ever known! They are either on or off!

By leaving it switched on, it seems. I found this amongst quite a lot of useful stuff on Yahoo!:

http://www.byebyestandby.co.uk/bbsbfaq.html

This is a quote from near the bottom of the page:

Q: Which appliances are the main Standby offenders?

* Dishwashers left "on" at the end of their cycle consume 70 per cent of the power used when they are running.
* The average television is left on standby for up to 17.5 hours a day. Last year Britain's 62 nmillion television sets consumed about 8 per cent of their energy consumption in standby mode.
* Washing machines use just under 20 per cent of their normal electricity requirement on standby.
* Tumble-dryers can use 38 per cent of power while waiting at the end of a cycle.
* If lights were turned off when not in use it would prevent 375,000 tons of CO2 emissions mand save £55m in bills.
* There is little difference between the power requirement of digital receivers when they are on and on standby.
* Experts say the total power used while an appliance is on standby can equal electricity used during the time it's on.
* Other appliances with high standby power use are cordless telephones, radios and stereos.*

[Annpan]

We switch off as much as possible at the wall, especially at night- makes sense, every little helps but I can't see that a tiny power on light on the dishwasher can use anything like the power used when working pumps and heaters for the water

As far as I know when something is on standby the capacitors (like tiny batteries) are kept charged, ready to shoot into action at any point... so even items - which perhaps just have a tiny light on - are still using electricity to keep those capacitors charged all the time.

But you are right the led light uses such a tiny amount of energy that it is practically nothing. It is the inside bits that are using up the energy though

[wulf]

Is there a cheap, easy way to measure how much power something consumes? I have a vague recollection that you could get a device to plug things into but I don't know enough of the details to easily search.

Wulf

[Millymollymandy]

I don't understandhow you can leave a dishwasher or washing machine on standby. There's isn't such a thing on any I have ever known! They are either on or off!

By leaving it switched on, it seems. I found this amongst quite a lot of useful stuff on Yahoo!:

http://www.byebyestandby.co.uk/bbsbfaq.html

This is a quote from near the bottom of the page:

Q: Which appliances are the main Standby offenders?

* Dishwashers left "on" at the end of their cycle consume 70 per cent of the power used when they are running.
* The average television is left on standby for up to 17.5 hours a day. Last year Britain's 62 nmillion television sets consumed about 8 per cent of their energy consumption in standby mode.
* Washing machines use just under 20 per cent of their normal electricity requirement on standby.
* Tumble-dryers can use 38 per cent of power while waiting at the end of a cycle.
* If lights were turned off when not in use it would prevent 375,000 tons of CO2 emissions mand save £55m in bills.
* There is little difference between the power requirement of digital receivers when they are on and on standby.
* Experts say the total power used while an appliance is on standby can equal electricity used during the time it's on.
* Other appliances with high standby power use are cordless telephones, radios and stereos.*

Well that's a bit of a bummer about dishwashers, because ours goes on when we go to bed cos it's off peak electricity. Then of course it stays 'on' all night with the lights still on.

Why can't they make machines that turn off when the cycle is finished?

[hamster]

Could you get one of those timer plugs?

[Millymollymandy]

Erm I don't quite see how it'd work as the socket is behind the dishwasher somewhere and it's all built in.

[MKG]

Those figures provided by Riff-Raff have me worried, and you make a very valid point, MMM, in saying that a lot of connections are not accessible enough for a straightforward mechanical timer switch to be realistic. Old electrical engineering routes in my brain are beginning to open up again ... now if only I can work out what the difference is between a machine in a quiescent phase and a machine that has finished its cycle and gone over into standby mode ...

Thinking ...

[The Riff-Raff Element]

The thing that dawns on me is that it does seem to require a mechanical act to truly turn something off: a switch has to be thrown, or a relay tripped or a timer has to tick round. Could it be - and there must be someone who knows this - could it be that it is impossible to properly disconnect something purely using electronics?

Just a thought.