# iPhone power usage over a year

Let’s say I have to charge my iPhone 3gs completely every night. If I understand correctly from http://en.wikipedia.org/wiki/IPhone_3GS, that means I’m consuming

3.7 V * 1.219 Ah = 4.5 Wh. If I pay 10c / kWh for electricity (I generally pay less, but I think some parts of the country pay more, so I’ll go with that), it looks like my annual electricity costs to my cell phone are

4.5 Wh / 1000 * 10c * 365 ~= 16c.

Is my math right? That seems unbelievably cheap.

Your math is right. Your methodology is wrong. You’ve got what it’d take to run the iPhone hardware.

I don’t know about the 3GS, but my iPhone 4 charges at 5W (5V * 1A) according to the charger. A full charge takes a very rough 3 hours, so that’s 15W/h per day. So thats… 50 cents per year.

That does seem like a bargain!

1. You may recharge more than once a day.

2. Hopefully, your expensive, sensistive electronics are run through an expensive line protector.

3. If you are in an air conditioned environment, the air conditioner has to pump out the heat from your charger and line conditioner.

Even given all that, it looks like a real bargain, compared to a 100w stereo.

Even more of a bargain if you charge it each day in your car!

To be pedantic, 1A is the maximum output current of the charger. It doesn’t actually run at a constant 1A current for 3 hours; the current is reduced as the battery gets more fully charged. But I guess your number serves as an upper limit. (Though technically, you didn’t account for the inefficiency of the charger… But that’s probably less than a 20% correction.)

One other factor to consider: if the charger is plugged in all the time, it’s wasting some power all the time. I don’t know the actual number for the Apple charger though.

Actually, charging from your car is just drawing the extra current from the alternator, which gets it from burning gas. Power from the utility company is cheaper than power produced by burning gas in an internal combustion engine. So charging it in your car may make it two or three times more expensive.

But, if you are going to be burning that gas anyway…

As it’s tangentially related to the conversation, just wanted to mention this device that shows a wavering blue light as it charges, concievably so you can have an idea of when it’s near completion. Kinda cool, especially if we see the solution expand to other energy charging and consumption devices.

But the alternator does increase the load on the engine, causing it to burn more gas than it would otherwise.

tanstaafl.

Oh. Learned something today…

Due to pumping losses in a gasoline engine, they are quite inefficient at the low to mid loads usually encountered. This being what hybrids avoid. Point is, that small and even largish additional loads (like AC) increase fuel consumption far less than the added HP load would suggest.

This is more true for cars with large engines than for those with smaller engines, and much less true for Diesels than spark engines.

Of course some of that gets mitigated by the fact that automotive alternators are built for low cost and longevity, efficiency be damned.

Charge it at work. Savings galore!

This is what I do - I’m taking the 20c (now corrected for charger inefficiency) a year and socking it away in my IRA. I’ll be sipping Manhattans while y’all eatin’ dog food!

don’t forget to unplug!

that vampire power brick is sucking you dry for at least 50 kilowatts, ~\$5.00, a year!

Do you mean KWH?
That’s 136 WH/day, or 5.7W/hour. Since all of Apple’s power cubes are energy-star rated, they can’t consume more than 1W when idle, so your \$5/year estimate is about 5x too high.

I would be really surprised if the power cubes used close to 1W when unplugged. I don’t have a good tool to measure power below about 3W. Do you know of a cheap meter for that?

It’s pretty hard to measure such low power accurately.
But, the current crop of energy star rules require <.5W at idle, and that’s a pretty hard target to meet. I would guess that currently, most small switching regulators consume around .8-1W unloaded.