Am I doing this wrong?

[Okjoek]

I'm trying to calculate how much energy certain home appliances use. I'm looking at my S7 phone charger:

 

"Input: 100-240V, ~50-60Hz, 0.50A

Output: 9.0V, 1.67A or 5.0V, 2.0A"

 

Now I only took two classes on electronics in HS, but I should be multiplying the Input Voltage & Amperage to know how many Watts it uses right? Well it has two voltages listed 100 and 240. I'm assuming this difference has something to do with fast-charging needing to use more force so I'm using 240V as a worst-case scenario just to be safe.

 

That said .5 x 240 = 120W which sounds ridiculous for a phone charger to be drawing. Am I doing something wrong? Is it a DC measurement and not AC?

[Guest]

You need to calculate the output wattage, then you can know how much the phone pulls. But im no expert too, i just think that the phone should pull about 20w when fast charging.

[Blasteque]

You are looking at ratings, not actual consumption.  You'll need a meter to determine actual consumption.  The output power is 9V x 1.67A or 5V x 2A, which equals 15W or 10W; these numbers will be close to the actual consumption, but not exact.  The .5A on the input is basically a not-to-exceed limit on that class of electrical device.

[Okjoek]

1 minute ago, Some Random Member said:

You need to calculate the output wattage, then you can know how much the phone pulls.

Oh so the input is the wrong thing to be measuring? I guess I should be looking at it like a PC PSU where the PSU Wattage isn't actually what is getting used, but instead it's the components themselves.

[Dujith]

The 0.5 is more a rating number then actual draw.

The adapter will be around 80% effective so if its on full load: 9*1.67 = 15.03W the the input would be ~18.8W

[Mira Yurizaki]

5 minutes ago, Okjoek said:

Now I only took two classes on electronics in HS, but I should be multiplying the Input Voltage & Amperage to know how many Watts it uses right? Well it has two voltages listed 100 and 240. I'm assuming this difference has something to do with fast-charging needing to use more force so I'm using 240V as a worst-case scenario just to be safe.

The 240V is because parts of the world use 220-240V. The rest use 100-120V. The label is saying what voltages it can input from the mains when you plug it in, and since it's a 100V-240V input (at 50Hz or 60Hz), it can be used in any country's mains electricity supply. You just need to find a passive adapter if the plug doesn't fit.

5 minutes ago, Okjoek said:

That said .5 x 240 = 120W which sounds ridiculous for a phone charger to be drawing. Am I doing something wrong? Is it a DC measurement and not AC?

It won't likely draw that much current, which that value is an "up to" value. And lower voltages will draw more current for the same amount of power.