# charging with car's AC - how many devices can be charged

Started Jan 31, 2014 | Discussions thread
Re: charging with car's AC - how many devices can be charged

PenPix wrote:

Is the inverter rating an output of 150 watts and 110 volts, (not input of 150 watts)? You can correct me if this is not what it shows

A quick Google search shows a 5 year old mcBook pro consumes a maximum of 85 watts. If you inverter is rated with an output of 150 watts, you have a safe overhead for using the devices together.

In my experience with small inverters the 150 watts is the input so the maximum output power is lower. However, your conclusion is right anyway. The 85-watt rating for the MacBook is the maximum draw if the battery is almost discharged and the computer is running a very processing-intensive program with lots of graphics.

The maximum car alternator output power to charge its battery is over 700 watts even for a small car. The fuse for the cigarette lighter is usually either 10 or 15 amps. If it's 10 amps (120 watt draw) the fuse will protect the inverter and its load. (Good reason to have a spare fuse.) If it's 15 amps (180 watts) then something else (such as the inverter's fuse, if any) will blow or the inverter will shut off if it has that capability (perhaps thermal protector).

If I were the OP, I'd get a second battery for the laptop. It can provide USB power for other devices such as a USB disk drive. I'd also do a complete dry run at home with a small car and a largely discharged laptop battery plus all other devices being charged.

And, I'd buy a digital volt meter with auto-ranging (a feature that makes it easier to use). I would also only charge up the laptop when the car is running. If the car battery voltage drops below 12 volts then, depending on temperature and engine size, it's time to start it and get the alternator running. Most car batteries stabilize at 12.3+ volts when topped up. (That's why a good digital voltmeter is useful.)

(One more thing: the MacBook has a good capability to show its battery charge status.)

John1940me

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