Power Consumption / Running Costs Questions :

Sphinx-BMW

Active Member
Hi,

Been looking at a 46" Panasonic Plasma.

Power Consumption is 440w.

Reason I ask - Is that I trying to calculate the running cost of a Plasma.

Whats the kw/h on this? Does it not consume 440w as soon as its switched on?

Thanks.
 

Jon P

Active Member
Hi.

The figure will be the rated power consumption ie the maximum it will use. it will likely use on average around 280 W during normal use. A plasma varies its power consumption depending on the brightness of the image.
 

charles_b

Active Member
Appliances are rated with Wattage and you are charged for electricity at a pence per KiloWatt Hour (1000Watts).

So a TV running at 250 Watts would consume a Kilowatt in 4 hours of use.

Assuming 250W and 10 hours per day, every day the cost in a year would be:

250 * 10 * 365 = 912,500 Watts (912.5 KiloWatts)

Currently Electricity Units are around 18p (1 Unit = 1 Kilowatt).

So this TV would cost 912.5 * 0.18 = £164.25 per year to run this TV

You can use this formula for any electrical item just change the Rated Wattage.

Hope this helps
Charles
 

charles_b

Active Member
Simply Yes, it's probably a bit more complicated than that (I'm no Physicist)

TV's are probably the best guide for determining usage, as it's fairly constant Power consumption.

Other appliances, such as a Kettle might be rated at 2KW or 3KW, but it only gets used for 5 minutes at a time, so the actual Watts used would be (I'm using 2.4 for ease of maths!)

2.4KW * (5/60) = 200 Watts. So it would take 5 Cups of Tea/Coffee to use a KiloWatt Hour.

I think the simplest thing to remember when looking at power consumption is what the Wattage is, and how long will it be on for.

Stand-by Wattage is also important. Apart from TV's, most other AV equipment sits in Stand-by when not in use. If a DVD player uses 10W in stand-by, it takes 100 hours to use a KWh, but that's only 4 days!, so it uses 90KWh every Year (£18). That doesn't include the Power consumption when in use.

When you've got a stack of AV equipment, this starts to rack up to large sums.

Best investment is to get a Power cutting device, which cuts power to all non-essential equipment when you turn off the TV. I have one for all my Computer equipment, and apart from PVR's which need to be on all the time, everything else is on another one.
 

charles_b

Active Member
Sorry for confusion on KWh prices - :suicide: I just checked mine and it's gone down to 10.2 pence (Early last year it was nearly 18p on my tariff), and I just negotiated a 25% rebate on this also, so it's around 7.5p :lesson:

So at least our AV costs are cheaper.! The Calculation still works, just replace the 0.18 with the price that you pay (in this case 0.075)

By the way - do you take the Standing Charge into consideration? I'm paying around 24p per day.
 
Last edited:

choddo2006

Distinguished Member
Thanks for the quick reply.

This is what I thought initially.

Are all power consumption figures for appliances based on per hour then?

No, it's a confusing one this. Watts, the measure of power, has no time dimension to it at all.

But electricity usage is measured in power x time. Hence kWh but it could just as easily have been Ws.

So a device which consumes 1000W and is on for an hour will have used 1kWh.

A device which uses 1000W which was on for 1 minute would be 1/60 kWh

charles_b said:
Other appliances, such as a Kettle might be rated at 2KW or 3KW, but it only gets used for 5 minutes at a time, so the actual Watts used would be (I'm using 2.4 for ease of maths!)

2.4KW * (5/60) = 200 Watts. So it would take 5 Cups of Tea/Coffee to use a KiloWatt Hour.

I think the simplest thing to remember when looking at power consumption is what the Wattage is, and how long will it be on for.
I've got a degree in physics and I still find this hard to explain :)

But in your example, I wouldn't call 2.4kW * 5/60 = 200 Watts because you're mixing all sorts of units there.

Your maths is right but to keep it clean, since you need to get to kwh, I'd say something like that a kettle used for 5 minutes (1/12 hour) twice a day for a quarter or roughly 92 days (the usual billing period)

=2.4 (Kw) * 2 * 1/12 (hours on / day) * 92 (number of days)

cos then the units work

you have Kw * hours/day * day - the day/day cancels out leaving you with kWhours

and that gives you 36.8 kWh

I so hope that's right :D
 

PSM1

Distinguished Member
There was an article on the Gadget Show a couple of weeks ago looking at the cost saving of 'Eco' modes on new TVs. Most of these reduce the brightness of the TV to achieve the saving hence compromise the PQ. Worked out the 'Eco' modes saved about £10 to £30 in a year if I remember right so in my mind not worth it. I would prefer to pay the little extra and actually have the screen operating at full performance as the extra pleasure in watching is easily worth the extra cost.
 

charles_b

Active Member
I've got a degree in physics and I still find this hard to explain :)

I'm well used to weird equations, we calculate all sorts of daft things where I work, such as estimated GFR which uses all sorts of things to determine if you have Renal dysfunction.
Glad I chose Biochemistry instead of Physics though....although the physics still helps me in everyday life!

All Scientists Together! :thumbsup:
 

rewerb

Well-known Member
But in your example, I wouldn't call 2.4kW * 5/60 = 200 Watts because you're mixing all sorts of units there.
Nothing wrong with that.
Kettle is rated in Kw/hours. He's multipled by the number of hours in use to arrive at the kwattage used. (200w or 0.2Kw)
 

choddo2006

Distinguished Member
I'm well used to weird equations, we calculate all sorts of daft things where I work, such as estimated GFR which uses all sorts of things to determine if you have Renal dysfunction.
Glad I chose Biochemistry instead of Physics though....although the physics still helps me in everyday life!

All Scientists Together! :thumbsup:

In a semi-lucid moment on the 0650 flight this morning, I also realised that I was talking bobbins about there being no time dimension to Watts.

They are of course, Volts x Amps

and Amps are Coloumbs per second.

So Watts are a unit of energy consumption per second. No great shock there (ohohohoho)
 

choddo2006

Distinguished Member
Nothing wrong with that.
Kettle is rated in Kw/hours. He's multipled by the number of hours in use to arrive at the kwattage used. (200w or 0.2Kw)

Na, kettle is rated in kW, not kW/h


I fear this has strayed far beyond being useful to anyone now though. Sorry.
 

stranger

Well-known Member
Simply Yes, it's probably a bit more complicated than that (I'm no Physicist)

TV's are probably the best guide for determining usage, as it's fairly constant Power consumption.


Stand-by Wattage is also important. Apart from TV's, most other AV equipment sits in Stand-by when not in use. If a DVD player uses 10W in stand-by, it takes 100 hours to use a KWh, but that's only 4 days!, so it uses 90KWh every Year (£18). That doesn't include the Power consumption when in use.

When you've got a stack of AV equipment, this starts to rack up to large sums.

Just for info. the later Pioneer tvs use less than half a watt in standby.
 

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