Airplane power vs. car power

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  #1  
Old 06-29-08, 10:23 PM
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Airplane power vs. car power

Apple(tm) sells an airplane power adapter, that does EmPower and 20mm 'can' plugs. Now, that 20mm 'can' fits nicely in a car cigar lighter receptacle. However, for whatever reason, it doesn't provide power to a laptop when hooked up.

Whiny Do-It-For-Me question: is there something really really simple one can do to draw even run-but-not-charging power from a car to power a macbook?

Less Whiny Help-Me-Help-Myself question: does anyone have specs/pinouts/voltages and such for car cig. receptacles vs airplane non-EmPower receptacles? My GoogleFu is particularly weak since every link seems to be trying to sell me something.

Thanks!
 
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Old 06-29-08, 10:42 PM
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Majorty of automove electrical system is 12 volt neg grounded system while aircrafts it can be either 12 or 24 volts depending on size very small personal aircrafts generally used 12 volt while the rest of small standard aircraft and larger used 28 volts system.

But however if you are tempting to use wallwart [ plugin transformer ] on Aircraft 120v system the answer is Just don't go there for safety reason due the AC system in aircraft is 400HZ while the household system in North America is 60 HZ while European and other area run on 50HZ.

Merci,Marc
 
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Old 06-30-08, 08:47 AM
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AFAIK, the airplane plug is a tad smaller than an auto power port. Also, the power port on a car may be switched with the ignition.
 
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Old 06-30-08, 08:52 AM
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Car power is very "dirty", with load dump transients (negative 300 volts) from the alternator.
Don't run the engine while powering your computer, or buy a filter that blocks these power spikes.
Aircraft power is probably filtered.
 
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Old 06-30-08, 12:54 PM
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No joy.

According to Apple, it won't work.
EmPower Airline Adapter for PowerBook G4 & iBook (Dual USB)

Straight-thru cable for 15V DC EmPower™ systems. Ultra-light, ultra-compact design. EmPower™ is the number one choice of airlines around the world. Adopted by almost 40 airlines, there are over 86,000 seats on almost 1600 aircraft using this system. Note: This adapter will allow you to use your PowerBook for extended periods of time however 15V DC will not recharge your battery. United and most non-US carriers use EmPower systems. Please check with your airline for availability. Some carriers (eg. American Airlines) use a car cigarette lighter socket to provide laptop power. The EmPower Air Adapter is not compatible with these sockets.
(Emphasis added)
 
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Old 06-30-08, 05:18 PM
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Let's try this again.

"But however if you are tempting to use wallwart [ plugin transformer ] on Aircraft 120v system the answer is Just don't go there for safety reason due the AC system in aircraft is 400HZ while the household system in North America is 60 HZ while European and other area run on 50HZ."

Right. I'm not trying for AC. I'm wanting to DC-power a laptop off a DC system in a US automobile.

"AFAIK, the airplane plug is a tad smaller than an auto power port."

The metal contacts on the side of the plug depress when inserted in the car's receptacle.

"Also, the power port on a car may be switched with the ignition."

Noted. But my car's receptacle is always-hot.

"Car power is very "dirty", with load dump transients (negative 300 volts) from the alternator."

Right. It was planned for running while the engine is cold. After all, I'm driving.

"According to Apple, it won't work."

Which is why I'm asking DIY-ers. If it were just a matter of plugging it in, I'd've gotten that on my own.

"Some carriers (eg. American Airlines) use a car cigarette lighter socket to provide laptop power. The EmPower Air Adapter is not compatible with these sockets."

This is not the product I have. The one I have has the can-style adapter to mask the EmPower plug into a cig-style plug.

SO. Back to the original question: what's the pinout/voltages/etc on car cig-lighter receptacles and DC-not-EmPower receptacles?
 
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Old 06-30-08, 09:29 PM
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The automotvite { Car } cig lighter socket the centre pin is postive while the shell is negtive grounded .

typically are 12 volt system but aircraft will varies a bit it will be either 12 or 24 { 28 volts } as you see my comment above but the aircraft can be floating ground system or either postive or negtive ground system it will varies a bit depending on which type of aircraft it involded.


Merci,Marc
 
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Old 07-01-08, 09:53 AM
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Lead-acid car batteries produce about 12 V when fully charged and lightly loaded [edit: Wiki says 12.6 V open-circuit]. The charging systems are coarsely regulated to produce 13.5 to 14.5 VDC (typically about 13.7 V). These are the voltages that will appear at the cigarette lighter with, as already noted, center connector positive. They are unregulated - that is, the voltage at the lighter socket will vary depending on battery charge and condition, load, and, when charging, sometimes engine speed.

The EmPower adapter I linked sounds like it needs 15 VDC regulated and just passes that straight to the DC connector on the computer. If that adapter is not what you have, can you provide specs, or a link, for the one you do have. If it is sold as an auto/airplane adapter (we have some of those at work), I would expect it to work in a car cigarette lighter; if it's sold as an airplane power adapter, then all bets are off.

The "Power Ports" on American Airlines are car cigarette lighter-type sockets. They are limited by the airline to 75W max, and cut off if you try to exceed that. The polarity is the same as US cars (center positive), but I don't know the voltage. Cigarette lighter "automobile" power adapters work fine with them, so it's probably in the 12-15V range.

This may not be the answer you want, but the easiest and best (IMO) solution would be to use a 115V AC inverter. Get one designed to power laptop computers - they produce a good replica of a 60 Hz sine wave instead of a square wave - and run your regular AC power supply from that. This has the advantage that you don't have to get a new one when you get a new laptop (if it's big enough), it should clean up the DC so you can use it with the engine running if needed, plus you can charge your cell phone and laptop battery or other geegaws on the road.
 

Last edited by ByteWrangler; 07-01-08 at 10:12 AM.
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