Which uses more electricity?

Solomon_Broad

I've just done some testing with my Kill-a-watt, and found the following.

Kitchen TV - 15" Alba (about 12 years old, on it's last legs...)

Running - 45w, 0.32amp
Standby - 4w, 0.03amp

Living room TV - 21" Pacific (less than 18 months old)

Turning on - 5w, 2.34amp (this lasted a second, no longer. TV turns on into standby).
Standby - 3w, 0.03amp
Running - 45w, 0.35amp (this fluctuated between 29 and 35amp).

Both TV's are the CRT type.

Cardew

Solomon_Broad wrote: »

I've just done some testing with my Kill-a-watt, and found the following.

Kitchen TV - 15" Alba (about 12 years old, on it's last legs...)

Running - 45w, 0.32amp
Standby - 4w, 0.03amp

Living room TV - 21" Pacific (less than 18 months old)

Turning on - 5w, 2.34amp (this lasted a second, no longer. TV turns on into standby).
Standby - 3w, 0.03amp
Running - 45w, 0.35amp (this fluctuated between 29 and 35amp).


Both TV's are the CRT type.

I don’t know what a ‘kill a watt’ is but(assuming you are in UK) it is inaccurate or Ohm’s Law is wrong.;)

Power(Watts) is the product of Voltage(Volts) and Current(Amps)

So assuming your supply is the nominal 240V 50hz supply your figures cannot be correct.

e.g. The Alba TV when running and drawing 0.32amps would be consuming
77W (240v x 0.32A) not 45W

The percentage errors on the other readings are out by an even greater percentage margin.

Assuming the Kill a watt is a fairly simple power measuring meter, I would be inclined to accept the Wattage readings as being the more accurate.



Please read 2 posts below -

Jonesya

Cardew wrote: »

Power(Watts) is the product of Voltage(Volts) and Current(Amps)

So assuming your supply is the nominal 240V 50hz supply your figures cannot be correct.

e.g. The Alba TV when running and drawing 0.32amps would be consuming
77W (240v x 0.32A) not 45W

I'm afraid that in this case that is incorrect, that only holds for AC systems with loads operating at unity power factor, such as heaters, incandescent lamps, possibly SMPS with active PFC.

You've got to consider the power factor of the load; it's a television so will have some form of electronic power supply (SMPS or simple rectifier type) which will draw a highly distorted current waveform so it will not be operating at anywhere near unity power factor, particularly as it's an old TV set so probably doesn't have any form of power factor correction.

Hence the TV may be drawing 77VA (Apparent Power = V x I) but only consuming 45W (Active Power = V x I x PF) with PF = 45/77 = 0.58

Cardew

Jonesya wrote: »

Not quite I'm afraid, that only holds at unity power factor (loads like heaters, incandescent lamps). You've got to consider the power factor of the load and as the television will probably have some form of switch mode power supply it's unlikely to operate at unity power factor.

Hence the TV may be drawing 77VA but only consuming 45W.

All non techies please ignore below!

You are quite right!

Before I posted I actually checked the PF of 2 of my TVs and they were as close to unity(0.99) - my meter measures VA, Watts, PF and kWh.
- to make no difference(151VA/150W) so I didn't mention power factor; assuming that this would be the norm!

Anyway after reading your post I have just checked my third TV(a 6 year old Sony) and it has a PF of 0.82. :eek: That will teach me to make assumptions:o

I thought I had read that for may years all TVs had to have PF correction - obviously not so long ago.

So the OP's figures are probably accurate - and of course for the purposes of this thread it is the Wattage that is important. I have added to my post bringing your post and this to peoples attention.

Crawls away with egg on face!

Solomon_Broad

I can say with some certainty that the wattage reading is correct. I did as you suggested, and tried several lightbulbs in a lamp. It measured an 18w ESB, a 40w, 60w and a 100w incandescent bulb correctly. Oddly, it read an 8w ESB as only being 6w? Same lamp, same socket, etc. I even tried the other bulbs again, and it got them correct again.

The neighbours must think I'm barmy keep switching the light on and off. :rotfl:

rygon

you will find the PF will change throughout the day as well due to demand.

MarkyMarkD

Not surprisingly all the government tosh about TVs using "almost as much" energy on standby as switched off is tosh. :rolleyes:

We have previously had to replace the on/off switch on TVs which have been subjected to fairly normal levels of use, costing us £50 or so. That's a lot of money compared to the amount of extra electricity supposedly used on standby.

Need_More_Money_2

MarkyMarkD wrote: »

Not surprisingly all the government tosh about TVs using "almost as much" energy on standby as switched off is tosh. :rolleyes:

We have previously had to replace the on/off switch on TVs which have been subjected to fairly normal levels of use, costing us £50 or so. That's a lot of money compared to the amount of extra electricity supposedly used on standby.

And I suspect some people would just replace the TV. Contributing to wasted energy in the production of new TVs.