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On a laptop charger adapter it is written '65 Watt'. When I am using that laptop plugged into an AC socket, does it mean that it consumes 65 watt per second?

I think it actually depends on usage. But is the 65 watt the maximum power consumption for this laptop, or can it consume more than that?

However, if it consumes more than 65 watt then the extra power must be taken from battery; but the battery also gets charged simultaneously and it remains fully charged. So doesn't it mean that the laptop uses less than 65 watt, because the maximum capacity of the charger is 65 watt?

Fsalad
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3 Answers3

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Just to clear up something first of all; it's a minor terminology issue, but:

does it then consumes 65 watt per second

A watt is measure of energy per unit time, specifically:

The unit is defined as joule per second

However, this is a noted area of confusion, so don't feel bad about it at all!

Typically a laptop will consume less power than its adapter will allow for. So in your case it will normally consume less than 65W. In normal operation it should not consume more power than the adapter sold with it can supply.

(You can test this by plugging the laptop into an energy usage meter/monitor (such as a kill-a-watt) and taking a reading while it is active.)

You can get into situations you describe in the last part of your question if the charger is incorrect for the laptop and cannot supply sufficient power1. This situation is more common with mobile phone / tablet chargers. However, I am not certain of the behaviour if the laptop continued to draw more power than the (incorrect) adapter could supply. I suspect it wouldn't charge, may discharge the battery or may not, and the operating system may shut down after a warning.

See also Using a higher wattage charger for my netbook

1: The last time I saw this was with a damaged charger, and I recall getting a warning notification to the effect that the battery would not charge. Disclaimer: dodgy recall, years ago, possibly incorrect etc

Community
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bertieb
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To accurately measure the total power consumption of the laptop, we would have to remove the battery and have it run off the power adapter while connected to a wattage measuring device such as a Kill-A-Watt meter.

If we can settle for a ball park figure, then a motherboard power monitoring software can be used to see how much power the CPU is consuming. For example, Hardware Monitor.

Here is an example of Hardware Monitor showing the current power draw of a computer's CPU.

enter image description here

CausingUnderflowsEverywhere
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To simplify, the question ought to be; how many watts per hour does a AC powered charger designed to power a DC powered device that requires 65 watts to power it require in units equal to watts per hour.

I am guessing more than 65 watts per hour due to the conversion from AC to DC.

I do not know and am guessing based upon limited knowledge. but the conversion is costly and if the cost was 20%, then the cost would be 13 watts (20% of 65). So the AC power would require 65 + 13 = 78 watts of AC power to yeild 65 watts of DC power per hour.

Does this make sense?

Am I wrong?

Max McByte
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