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Power Consumption

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Electroenthusiast

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On what factors does Power consumed by electronic appliance depend on?
Ex: Audio Amplifier:Does it depend on the magnitude of output sound?
Television : Does it depend on the brightness/quality of the picture?

Is it possible to calculate the Power consumed of electronic appliance using a multimeter?
Hint : P=V²/R
 
The output stage of an audio amplifier will certainly take more power when the sound is louder, unless it is a Class A amplifier. The power consumption of tuners, CD players, MP3 players that don't directly drive the speakers is likely to be nearly constant for any level of sound.

LCD televisions use most of their power to provide the backlight for the screen. The power consumption does increase as the screen is brighter. One of the monitors at my work is running from a power supply with an ammeter, and the current varies with the brightness settings. That doesn't usually mean that it uses more power if the image is brighter, because the backlight is normally constant as the image changes.

Televisions with LED backlights might be able to reduce the power if the image is dark. I'm not sure about whether they do or not.

I think that CRT televisions use fairly constant power.

You can't measure the power of an appliance by measuring the input resistance, unless it is a simple heater. You need to measure the current that it takes. One of those plug-in power meters would be fine.
 
Measuring the AC current isn't good enough (unless it's a purely resistive load such as a heater to light bulb) because it doesn't take the power factor into account. In order to measure the power properly, you need a power meter.
 
LCD televisions use most of their power to provide the backlight for the screen. The power consumption does increase as the screen is brighter. One of the monitors at my work is running from a power supply with an ammeter, and the current varies with the brightness settings. That doesn't usually mean that it uses more power if the image is brighter, because the backlight is normally constant as the image changes.

Yes it does, most modern LCD TV's dynamically alter the brightness of the backlights, it's how they achieve such high contrast ratios.

Televisions with LED backlights might be able to reduce the power if the image is dark. I'm not sure about whether they do or not.

Just as CCFL's do, LED's do as well.

I think that CRT televisions use fairly constant power.

No, they use more power for more beam current, they vary more than LCD's (of whatever type), and probably more than Plasma as well.

You can't measure the power of an appliance by measuring the input resistance, unless it is a simple heater. You need to measure the current that it takes. One of those plug-in power meters would be fine.

If you want to do it with a multmeter, it MUST be a true RMS one - but as you say, plug-in power meters are dirt cheap these days.
 
One of the monitors at my work is running from a power supply with an ammeter, and the current varies with the brightness settings. That doesn't usually mean that it uses more power if the image is brighter, because the backlight is normally constant as the image changes.
Yes it does, most modern LCD TV's dynamically alter the brightness of the backlights, it's how they achieve such high contrast ratios.
Thanks. The monitor that is run though an ammeter is a few years old, and it's current doesn't vary as what is on screen changes, but on a computer there are almost always some white pixels, so the backlight would have to stay on its set brightness.
 
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