Wall Plug Power Inverter

December 16, 2005 9:11 AM

Power Inverters for cars - the thing you plug into your cigarette lighter, with a regular wall-plug on the other end. I bought one last night, for use with gadgets on a road trip. Thing is, they offer two types, excuse the B-st B-y links: this one (95W), which I bought, and a stronger one (150W) here - Question is, I went with the smaller cheaper one but I know nothing about power use for things. Should I return it for the larger, or is this sufficient power to charge a laptop, camera, PSP, ipod, etc? Mostly concerned with safety to equipment and car's electrical system. THANKS FOR YOUR ADVICE.

I hate that there is always a larger version of something to buy when you go out to buy something.

posted by Peter H to Technology (16 answers total)

You can look at the amperage of the devices you're plugging in to figure the power required:

assuming you're in the US, the power requirement is simply 110 Volts x current draw (in Amps). So, if you wanted to plug in a 200mA charger for your [insert electronic device here], you'd need 22W. Also, for most chargers, the amperage listed on the device is a maximum; if you have less current available, it won't do damage.

My instinct says that you'd probably be able to charge several of those items, but not all at once.
posted by JMOZ at 9:20 AM on December 16, 2005

Looks like AC adaptors for laptops average from about 50-80 watts. Read the label on yours for exact specs. Unless you plan on using a splitter and charging everything at once the smaller inverter should be fine.

In no case do you risk damage to your car. The cigarette lighter is fuse protected and capable of powering a much larger inverter than you are interested in.

In short, if the current unit you have works, I see no advantage to upgrading. Cheers.
posted by vaportrail at 9:20 AM on December 16, 2005

Should be fine for any of those things you listed. Now, if you want to run a hair dryer or microwave...
posted by boaz at 9:24 AM on December 16, 2005

Now, if you want to run a hair dryer or microwave...

Then you're pretty much out of luck, because you're not going to draw enough current through your cigarette lighter to do that regardless of the inverter.
posted by JMOZ at 9:35 AM on December 16, 2005

I tried (unsucessfully) to run a vacuum cleaner with mine
posted by Makebusy7 at 9:42 AM on December 16, 2005

Response by poster: Ha, Makebusy7, really? You know, with drive-ins still someone alive, would a popcorn popper work?


THANK YOU FOR THESE ANSWERS

Okay, layman (me) asks: how do you read the A/C plugs on your stuff? I'm confused by the difference in watts, amps, the use of a tilda ~ on things, etc.

Take for example on the PSP:
INPUT: 100V-240V~0.3A 50/60Hz
OUTPUT: 5V=200mA

Can someone explain these? And how it relates to the power description of the power inverter:

95W Power Inverter
* Single 110/120 AC outlet
* Power plug adjusts to 45 degrees for convenience
* 95W continuous power (190W peak)
* 10 amp fused
* Powers up to .9 amps

This is actually an electrical question I've been confused about for years, -Thank you-
posted by Peter H at 9:52 AM on December 16, 2005

Response by poster: Ha, obviously I understand
* Power plug adjusts to 45 degrees for convenience

But the other stuff, please if possible, translate. THANKS.
posted by Peter H at 9:56 AM on December 16, 2005

Many people do not realize how much power consumption some devices require. Twice in last season's Amazing Race: Family Edition reality TV show teams were unfairly penalized because the camera crews were using their SUV's batteries to charge their equipment, thus resulting in dead batteries.

It just goes to show that if you're going to charge something for more than 10-15 minutes you need to leave your engine running so your alternator can recharge the car's battery and replace the energy consumed by the devicees you are charging.
posted by camworld at 10:04 AM on December 16, 2005

Best answer: INPUT: 100V-240V~0.3A 50/60Hz

Okay, I'm assuming you're in the USA from your profile and therefore on 120 volts. So, multiply the current (A) by the voltage (120 V) to get watts. That gives you:

0.3 x 120 = 36 watts.

The output isn't particularly important, although if no input specs are given (illegal) then you can *guess* the wattage from the output wattage (volts * amps again) with a large efficiency margin (some devices are as much as 50% inefficient).

If they give you the current in mA (milliamps), divide it by 1000 before working it out.

> * 95W continuous power (190W peak)

The inverter can provide 95 watts of power forever without overheating. You can draw 190 watts for a very short while (perhaps only seconds) before it will start to overheat. The peak is useful for things that have motors or other mechanical devices, since they require a lot of power for a moment to start up, but less to run.

> * 10 amp fused

If the inverter short circuits, it will blow the fuse when it draws 10 amps (12 volts * 10 amps = 120 watts) from your car. Of course, the fuse *should* be a slow blow fuse since the above rating says it can draw 190 watts (impossible for a fast blow fuse) through a fuse that, at 12 volts, would only allow 120 watts through.

> * Powers up to .9 amps

120 * .9 = 108 watts

So, it powers almost .9 amps... not up to. :-)

HTH.
posted by shepd at 10:14 AM on December 16, 2005

Then you're pretty much out of luck,

True story: My brother had an old jeep that wouldn't start when the engine block got wet, which would happen whenever it rained a lot. So he kept a 300w inverter and a hair dryer in the jeep, he would blow the hair dryer onto the block until it started. He had to keep the speed on low and with no heat or it would trip off the inverter, but it usually only take a minute anyway.

And I don't see anyone mention it, but the ~ means it's AC, while a solid line over a dotted line in the same position means it's DC.
posted by boaz at 10:35 AM on December 16, 2005

Best answer: Peter H writes "Take for example on the PSP:
"INPUT: 100V-240V~0.3A 50/60Hz
"OUTPUT: 5V=200mA"

Input half means it will draw a maximum of .3*240=72W and the output half is saying it will deliver 5*.2=1W. Your PSP isn't very power hungry and the adaptor is probably wildly inefficient, I've seen efficiencies of 20% on some of those wall warts.

95w watts is barely marginal for most laptops. For example my laptop has a max input draw of 432W and an output of 120W. If you divide the output by the lower end of typical efficiency you get a draw of 120/.7= 170W needed on the input side. Even the 150 model wouldn't be enough which is why I went with a 400W model. But for most other consumer electronics (camcorders, gameboys, personal dvd players, ipods, digital cameras, etc.) 95W will be fine.

Most hot air popcorn makers pull 500-1500W so you'd be out of luck with those. Though a good hardware hacker could convert an AC model to DC for less than a $100 but it would draw more power than your headlights so make sure your engine was running while using it.
posted by Mitheral at 10:50 AM on December 16, 2005

I also tried (unsucessfully) to run a vacuum cleaner with mine. What I did do successfully in this process though -- and I don't quite understand how -- is destroy my alternator ... which in the ill-designed Ford Escape cost $800 to replace.
posted by fourstar at 11:38 AM on December 16, 2005

Best answer: Well, keep in mind that an inverter (even a high power one) still requires >=10 times the current of the device you're running. (120VAC for the backend /12VDC from the car battery).

If you do the math for a high wattage device (like a vacuum or a popcorn popper), you get quite large currents. If you're lucky, it'll blow a fuse. If you're very unlucky, you'll blow your alternator (like fourstar).

Moral of the story:
-Inverters are good for charging small electronics (pref. not all at once.)
-Inverters are not good for anything that draws a lot of current.

As a side point- most (if not all) of the devices you're talking about actually use DC. If one buys a DC/DC converter (to change 12VDC of the car to the input voltage of each device) and finds plugs for each item, one can charge their electronics more efficiently than going from DC to AC to DC. Of course, this would be quite annoying to do unless someone already makes a nice unit with all the different output plugs (and a way to make sure to get the polarity right!) Even then, you'd be limited to one voltage at a time, which probably means you'd not be able to charge all your devices.

Also, as an interesting aside for people like shepd who notice the inefficiency of AC/DC converters (used by most electronics)- that loss is why your power supply usually gets so hot; it's dissipating the wasted power.
posted by JMOZ at 12:00 PM on December 16, 2005

Note, you want to make sure you start the car first, then hook the devices up. If they're connected to power while you start the car, they may suffer from the fluctuations of electricity while the starter is engaged and the alternator spins up.
posted by knave at 12:02 PM on December 16, 2005

Response by poster: These are great responses, and extremely appreciated.

I have no idea what answer to mark as best, is it possible to mark the whole thread?
posted by Peter H at 1:14 PM on December 16, 2005

Best answer: [marks whole thread]

THANK YOU AGAIN.
posted by Peter H at 2:38 PM on December 16, 2005