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Thunderchild · 18th March 2007, 07:18 PM

Quote:

Originally Posted by Nigel Goodwin

The power consumption of an LCD and CRT are pretty much the same, bearing in mind that an LCD takes full power all the time, and a CRT depends on beam current (brightness). The 1/10th power consumption is a complete work of fiction - it's nothing like that, and may even actually be higher!.

I can turn the brightness of my CRT down to using 800 mA on 12 Volts perhaps I exagerated on 1/10th but mybe not 800 mA at 12 volts is like 10 watts my 15 inch LCD is the same size as my Dads 100 W 19" CRT so there in black and white i measured it personally

Hero999 · 18th March 2007, 07:31 PM

Did you measure you dad's CRT as well?

9.6W, even though due to losses in the PSU it's more likely to be 11.52W it still seems too good to be true.

**Nigel Goodwin** · 18th March 2007, 07:34 PM

My 19 inch LCD has a 12V 4.16A power supply, that seems about right for an LCD - a smaller one will take slightly less of course.

Comparing TV and LCD, LCD's usually take more power than similar size CRT sets, and Plasma take more again.

Thunderchild · 18th March 2007, 07:40 PM

Quote:

Originally Posted by Nigel Goodwin

Comparing TV and LCD, LCD's usually take more power than similar size CRT sets,

No as i said I measured it myself, yes hero999 a 15" LCD (and not a good quality one at that) can use as little 12 watts, 20 watts at normal brightness but if you just gonna browse the web you can turn it down on mine if the page has a white background it can be a bit dazzling at 100 % (20 watts - 1.4 amps on 12 volts) I was told that CRT monitors use up to twice CRT TVs because of the higher resolution or something but I have no founded proof of that

**Nigel Goodwin** · 18th March 2007, 07:48 PM

Did you use a true RMS meter to measure the current?, if not it bears no resemblance to the actual current - I had occasion to scope the input current of a switch-mode PSU the other day - I was surprised at the actual waveform I got, and it would completely ruin a normal meter reading (nothing near a sinewave).

Hero999 · 18th March 2007, 08:10 PM

You're better off looking at the current rating on the power supply, better still use a true RMS meter and measure the AC side.

Thunderchild · 18th March 2007, 08:36 PM

I measured between the 12 DC output and the power conector of the monitor, yes I cut the wire to put in my tester set to amps I measured it as DC, as for the wattage of the CRT I used a refurbished electric board meter the same one used to measure and bill you for you mains power consumption i got it at the electric shop as they are switching to digital meters now and puting the old mechanical ones on the market reset to 0.

Thunderchild · 18th March 2007, 08:37 PM

my LCD power supply does say 100-240 V 1.0 A of course as I said before it draws nothing of the kind

Hero999 · 18th March 2007, 10:13 PM

Just because you're measuring DC it doesn't mean that you can ignore the RMS meaurement, if a load isn't drawing a constant current then the reading using a DC meter multiplied by the voltage won't necesarely give you the power consumption. The only way you can gaurantee you're reading an accurate power reading is to use a power meter on the mains side because it will take into account of the power factor which a meter won't.

Thunderchild · 19th March 2007, 06:33 AM

well if you consider most of the power is used by the back light I think thats a pretty constant load isn't it ? as the monitors crystalls are refreshed 60 times a second that's a pretty constant figure it's not an electric car is it I think your being a bit too picky here the fact IS that LCD use a lot less than CRT, also the same power adapter has been used for other things as well, I have also used it to run a fan drawing around 3 amps and it go quite warm at the moment it is cold wile powering the monitor, any other silly exscuses to disbelieve my readings ? how would I measure RMS ? I only have a DC amp meter can I use it for ac with a rectifier in any way ? I could send 220 VDC to the power supply as the AC is getting immediately rectified any way.
Also remember my monitor is an old LCD (3-4 years) so possible comsumptions have even improved

Sceadwian · 19th March 2007, 06:38 AM

A good general rule of thumb is a CRT use around 120 watts of power and an LCD users about 20. There's no need to get any more precise than that

**Nigel Goodwin** · 19th March 2007, 07:43 AM

Quote:

Originally Posted by Sceadwian

A good general rule of thumb is a CRT use around 120 watts of power and an LCD users about 20. There's no need to get any more precise than that

The first is really too high, and the second really too low. Over the last decade or two, CRT set consumption has come down a great deal.

Pommie · 19th March 2007, 02:48 PM

The easy way to measure power consumption is heat. If it's warm it's using power. CRTs are warm LCDs aren't. I can't believe anyone is arguing different. If CRT's were power efficient they would use them on mobile phones.

As for not measuring true RMS. Are there no capacitors in them there power supplies? DC in is normally smooth and so is very close to true RMS.

Mike.

**Nigel Goodwin** · 19th March 2007, 02:54 PM

Quote:

Originally Posted by Pommie

The easy way to measure power consumption is heat. If it's warm it's using power. CRTs are warm LCDs aren't. I can't believe anyone is arguing different. If CRT's were power efficient they would use them on mobile phones.

LCD's do run warm - the smaller ones take less power than CRT's, but it's not a huge amount less - and larger ones take more than CRT's.

Quote:

As for not measuring true RMS. Are there no capacitors in them there power supplies? DC in is normally smooth and so is very close to true RMS.

As you say, measuring DC is the same as measuring RMS - but obviously doesn't account for the PSU losses (but it should be pretty efficient anyway).

Thunderchild · 19th March 2007, 05:49 PM

oh thank you oh gods what suddenly made you change your minds ? I do have to say I erred in comparing the 19" (got mixed up with what the original poster said) I was refering to 17",
My dads 17" CRT as stated by the manual uses 105 W my 15" monitor that is only 0.5 cm (0.2") smaller than the 17" CRT uses 20 watts AT MOST !
now I hate to immagine what that guys kids 19" CRTs are using more like 120 watts each at least so we are looking at 360 W for the monitors before counting 80-120 W for the computers he could easily be using 700 W for his kids computers and then wonders where it goes....

18th March 2007, 07:31 PM	(permalink)
Hero999 Experienced Member	Did you measure you dad's CRT as well? 9.6W, even though due to losses in the PSU it's more likely to be 11.52W it still seems too good to be true. __________________ What's so bad about Microsoft? Get Opera it's simply a superb browser.

18th March 2007, 07:34 PM	(permalink)
Nigel Goodwin Super Moderator	My 19 inch LCD has a 12V 4.16A power supply, that seems about right for an LCD - a smaller one will take slightly less of course. Comparing TV and LCD, LCD's usually take more power than similar size CRT sets, and Plasma take more again. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

18th March 2007, 07:48 PM	(permalink)
Nigel Goodwin Super Moderator	Did you use a true RMS meter to measure the current?, if not it bears no resemblance to the actual current - I had occasion to scope the input current of a switch-mode PSU the other day - I was surprised at the actual waveform I got, and it would completely ruin a normal meter reading (nothing near a sinewave). __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

18th March 2007, 08:10 PM	(permalink)
Hero999 Experienced Member	You're better off looking at the current rating on the power supply, better still use a true RMS meter and measure the AC side. __________________ What's so bad about Microsoft? Get Opera it's simply a superb browser.

18th March 2007, 08:36 PM	(permalink)
Thunderchild Experienced Member	I measured between the 12 DC output and the power conector of the monitor, yes I cut the wire to put in my tester set to amps I measured it as DC, as for the wattage of the CRT I used a refurbished electric board meter the same one used to measure and bill you for you mains power consumption i got it at the electric shop as they are switching to digital meters now and puting the old mechanical ones on the market reset to 0. __________________ I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately) my site:www.simons-photography.com http://rushdenrotaract.org.uk see also http://www.bigstockphoto.com/account...fid=m2URATYch5 http://www.redbubble.com/people/simonsphotography

18th March 2007, 08:37 PM	(permalink)
Thunderchild Experienced Member	my LCD power supply does say 100-240 V 1.0 A of course as I said before it draws nothing of the kind __________________ I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately) my site:www.simons-photography.com http://rushdenrotaract.org.uk see also http://www.bigstockphoto.com/account...fid=m2URATYch5 http://www.redbubble.com/people/simonsphotography

18th March 2007, 10:13 PM	(permalink)
Hero999 Experienced Member	Just because you're measuring DC it doesn't mean that you can ignore the RMS meaurement, if a load isn't drawing a constant current then the reading using a DC meter multiplied by the voltage won't necesarely give you the power consumption. The only way you can gaurantee you're reading an accurate power reading is to use a power meter on the mains side because it will take into account of the power factor which a meter won't. __________________ What's so bad about Microsoft? Get Opera it's simply a superb browser.

19th March 2007, 06:33 AM	(permalink)
Thunderchild Experienced Member	well if you consider most of the power is used by the back light I think thats a pretty constant load isn't it ? as the monitors crystalls are refreshed 60 times a second that's a pretty constant figure it's not an electric car is it I think your being a bit too picky here the fact IS that LCD use a lot less than CRT, also the same power adapter has been used for other things as well, I have also used it to run a fan drawing around 3 amps and it go quite warm at the moment it is cold wile powering the monitor, any other silly exscuses to disbelieve my readings ? how would I measure RMS ? I only have a DC amp meter can I use it for ac with a rectifier in any way ? I could send 220 VDC to the power supply as the AC is getting immediately rectified any way. Also remember my monitor is an old LCD (3-4 years) so possible comsumptions have even improved __________________ I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately) my site:www.simons-photography.com http://rushdenrotaract.org.uk see also http://www.bigstockphoto.com/account...fid=m2URATYch5 http://www.redbubble.com/people/simonsphotography

19th March 2007, 06:38 AM	(permalink)
Sceadwian Experienced Member Blog Entries: 1	A good general rule of thumb is a CRT use around 120 watts of power and an LCD users about 20. There's no need to get any more precise than that __________________ Curiosity killed the cat; That's why they have nine lives.

19th March 2007, 02:48 PM	(permalink)
Pommie Experienced Member	The easy way to measure power consumption is heat. If it's warm it's using power. CRTs are warm LCDs aren't. I can't believe anyone is arguing different. If CRT's were power efficient they would use them on mobile phones. As for not measuring true RMS. Are there no capacitors in them there power supplies? DC in is normally smooth and so is very close to true RMS. Mike.

19th March 2007, 05:49 PM	(permalink)
Thunderchild Experienced Member	oh thank you oh gods what suddenly made you change your minds ? I do have to say I erred in comparing the 19" (got mixed up with what the original poster said) I was refering to 17", My dads 17" CRT as stated by the manual uses 105 W my 15" monitor that is only 0.5 cm (0.2") smaller than the 17" CRT uses 20 watts AT MOST ! now I hate to immagine what that guys kids 19" CRTs are using more like 120 watts each at least so we are looking at 360 W for the monitors before counting 80-120 W for the computers he could easily be using 700 W for his kids computers and then wonders where it goes.... __________________ I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately) my site:www.simons-photography.com http://rushdenrotaract.org.uk see also http://www.bigstockphoto.com/account...fid=m2URATYch5 http://www.redbubble.com/people/simonsphotography

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