Car Power Inverter + Modified Sine Wave

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Level 1

15 points

Car Power Inverter + Modified Sine Wave

Hi everyone. I'm going on a trip soon so I am looking for a reliable car power inverter for my 2007 Macbook Pro. My car has 2 power outlets (12V / 120W). I know there is a 15A fuse, so the maximum it can handle is 180W, but of course I do not want to take that risk and stay around the recommended 120W. Because of this, it limits the number of choices I have concerning power inverters. I have seen one from Duracell called the Pocket Inverter 100. Here are the specifications:

AC Output Power (Max Continuous): 80W
AC Output Power (Peak): 100W
AC Output Surge Capacity (Peak): 160W
AC Output Voltage (Nominal): 120V
AC Output Waveform: Modified Sine Wave

So, this leads to a few questions:

(1) The MBP Magsafe Adapter requires 85W. However, this inverter can provide only 80W of maximum continuous power. Will this be sufficient to charge and run the MBP in the car?

(2) I searched around and read a few posts by others regarding pure sine wave. Now, this inverter has an output of a Modified Sine Wave. Will this be fine and will the Magsafe adapter be able to handle this?

(3) Are there any recommendations for car power inverters within these specifications?

Thanks for your help!

MacBook Pro 15'' | iMac 20'', Mac OS X (10.5.6), 2.2GHz ~ 120GB 5400RPM HD ~ 8600M GT | 2.66GHz ~ 500GB 7200RPM HD ~ HD 2600 PRO

Posted on Jul 22, 2009 10:46 AM

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Answer 1

Jul 22, 2009 10:51 AM in response to knp59

You can charge the MBP on less than 85watts, but it is not recommended, the battery will charge slower. And with no experience with your other two questions I cannot answer them.

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Answer 2

knp59 Author

Level 1

15 points

Jul 22, 2009 11:09 AM in response to a Mac user

a Mac user,

Thanks for your input. Does charging the battery slower actually affect it (ie. battery life, performance)?

In regard to the other two questions, hopefully other members can assist me in this matter!

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Answer 3

Jul 23, 2009 4:42 AM in response to knp59

The modified sine wave is not a problem. Given the lack of weight (no 60 Hz transformer) and extreme voltage range that the charger brick handles it has to be a switching power supply. The incoming AC is rectified to convert to pulsating DC which is then used to charge a capacitor. The capacitor voltage is fed to the switching power supply which generates the DC voltage that the MBP needs.

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Answer 4

knp59 Author

Level 1

15 points

Jul 23, 2009 7:53 AM in response to Retired Engineer

Retired Engineer,

Thanks for that information. Do you know if 80W will be sufficient to power my Macbook Pro despite the 5W deficit? Will this harm the MBP battery in any way?

Also, if my 12V car power outlet recommends 120W despite the 15A fuse, meaning a total possible power output of 180W, will it be okay to use a power inverter that has let's say, 130W of continuous power output?

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Answer 5

knp59 Author

Level 1

15 points

Jul 23, 2009 8:21 AM in response to knp59

I have one more thing to ask. I was just told that as long as the INPUT to the power inverter is less than 120W (what my power outlet recommends), it doesn't matter how much OUTPUT the inverter provides. For example, a power inverter is rated at a maximum power output of 400W, but on the input side, it only requires a 10.6-16V DC and 85W. So, despite the 400W output, the inverter only requires 85W from the car power outlet. Consequently, this inverter can be used in the car because its 85W input is less than the 120W maximum output of the power outlet. Is this true?

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Answer 6

Jul 24, 2009 5:04 AM in response to knp59

There is no way that an inverter, or any other device, can provide more power out than it is drawing from it's input source. If it's putting out 400 watts, it's probably drawing 800 watts since none of these devices is more than 50% efficient.

Get yourself a Kill-a-watt meter and measure how much power (watts) the MBP draws when it is turned on and charging a discharged battery. If it's 80 watts or less after the peak time limit for the inverter that you are interested in, then the 80 watt inverter will work. Personally I would get an inverter that is rated for at least 100 watts output.

I just measured mine and it's drawing 71 watts.

Message was edited by: Retired Engineer

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Answer 7

knp59 Author

Level 1

15 points

Jul 24, 2009 8:20 AM in response to Retired Engineer

True. The person who told me this said this was the case for industrial inverters, not the ones consumers purchase.

I might just get a 100W inverter with 80W continuous output (Duracell Pocket Inverter 100) or do you think I should get something like the Cobra CPI-150, which is rated at 150W but says that it will power anything under 150W, which I assume means it probably has a continuous output of around 120-130W. Will this cause problems with my 120W outlet or because the 85W drawn from the outlet to my MBP, technically it shouldn't have issues?

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Answer 8

Jul 25, 2009 4:13 AM in response to knp59

The 100 watt inverter will be fine. The inverter only puts out what the device plugged into it is asking for. It is capable of supplying 100 watts but will just as easily supply 1 watt if that is what it is being asked to provide.

As far as industrial inverters go, they follow the same laws of physics. It is impossible to get more power out than is being put in. Voltage or current, yes. Power, absolutely not.

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Answer 9

red_menace

Level 6

17,030 points

Jul 25, 2009 11:04 AM in response to knp59

You could also avoid the inverter completely and go directly from the DC source - something like the products at http://mikegyver.com/Store/index.html (they seem a bit pricey though, although that may be due to the proprietary MagSafe connector).

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