The difficulties of providing 110-volt power to your airline seat | Hacker News Reader

The difficulties of providing 110-volt power to your airline seat

theatlantic.com

66 pointscwan69 comments

Here's my personal solution. It works for all airlines. It can also power my Cradlepoint 4G hotspot and recharge my iPad, iPhone, and any device using USB power.

http://www.tekkeon.com/products-mypowerall.html

I bought a male Adaptaplug and a Magsafe cord from eBay, and after 5 minutes with a soldering iron, it works for my 13" unibody MacBook as well. I plan on upgrading to a 13" MacBook Air soon. I should be able to get 14 hours working time from this setup.

As a companion to my WiFi iPad, it's great. The Cradlepoint will run for 18 hours off of it. (I have the MP3450.) Not small enough for a pocket, but it fits fine in most laptop bags.

EDIT: I bet there's a business renting these things out to people at airports!

I've considered these, but I've been afraid of taking it through security without causing any headaches. Have you had any problems?

I've only had a problem with the Cradlepoint because I had it on and it was warm. The battery? I just put it in my carryon, and it's never been a problem. I spent almost $7000 in cheap airfares in the last year, so this has definitely been tested!

Wow, thanks a LOT. I've been looking for something like this forever, guess I didn't know what to search for.

Thanks -- I've been looking for one of these ever since APC stopped making theirs about four years ago.

Can't we just have exercise bikes linked to generators in economy class?

About time the lower orders did some work.

Hey, if I could get something out of it (like fare), I'd gladly pedal away.

On a long enough flight, I'd probably pay to pedal.

Come to think of it. Maybe we should have excercise bikes in 1st powering economy. On board gym?

I feel uncomfortable enough without the guy next to me having a heart attack and possibly killing me as he falls on top.

People sure do envision some strange failure modes for commercial flights...

"I wondered whether, as a technical matter, an airliner could actually produce enough power to keep a planeful of laptop users plugged in through a whole flight. [...] Short answer: No, you probably couldn't make this work."

Given that the power output of the engines of a Boeing 747 is 140MW [1], enough to power 15 copies of the Empire State Building at peak business hours[2], I find this impossibility a bit depressing.

[1] http://en.wikipedia.org/wiki/Orders_of_magnitude_(power)#meg... [2] http://depletedcranium.com/what-is-a-megawatt/

It is all about costs. Those engines are producing energy to keep the plane flying at 500mph. If you pull some power to spin an alternator then you need to run the engines faster and burn more fuel (which means you need even more fuel on board at takeoff to lug all of this extra fuel to the destination.) Add in the weight of the various inverters and equipment necessary to make this system safe on an airplane and I am surprised they even bother trying to run provide power to the seat at all.

Some math: 120V * 2A = 240W * 300 passengers = 72 kW. That's 1/50th of a percent of the existing power output of a 747. If you figure a $600 plane ticket, I'd gladly pay 1/50th of a percent ($0.30) of that for electrical power on the flight.

The numbers get a bit more complicated when you figure in the weight for transformers, alternators, inverters, etc. But fuel is not a major component of this. The math really doesn't support the assertion that it's not cost-effective.

"fuel is not a major component of this ... The math really doesn't support the assertion that it's not cost-effective."

How do you figure?

Say some extra weight delta_w in additional equipment is required, and say that the fuel required to complete a given flight is a function f of the plane's weight, and that the cost of the fuel is C. Further, let the lifetime maintenance cost of the new equipment be E, and the lifetime maintenance of the plane's structural components be g, also a function of its weight. As a rough approximation, the additional cost should be

E + C df/dw|_W * delta_w + dg/dw|_W * delta_w

(Note that, really, f is a function of both passenger power consumption and of weight, both of which we're varying here, but I'll buy your argument that df/dp|_P * delta_p is neglible in comparison to f(P,W))

The article asserts that one or both of the derivates in this equation are large enough that its product with delta_w is non-negligible (in fact, prohibitive). I'm guessing that df/dp is not the problem, which is the only term you really addressed.

72 kW is 1/19th of a percent of the output of a 747 (140MW).

More to the point, 240W is irrealistic for a laptop. Most laptops consume under 40W. With this better estimation, this is 1/117th of a percent.

Sure. But don't forget that adding a new feature to an airplane is going to take work. People have to figure out how all of this works, then other people have to test it, other people have to make sure it passes safety inspections, etc., etc., etc. Plus, then you have to retrofit old planes - or build new ones.

It's more than just fuel costs.

a (good!?) method would be, to install small power generating bikes on the plane, and use that to suppliment the power usage of passengers. You market the bikes as exsercise machines for the long journey to prevent blood clots.

The APU power is more relevant. THe 737 can have 90kW APU which should be enough for 1000 laptops under full load (while 737 cannot carry more than 215 passangers)

http://www.b737.org.uk/apu.htm

The APU doesn't run during normal flight, since the engine generators more than handle the electrical load.

As long as you don't need air conditioning. Or avionics.

This is a pretty snarky and relatively uneducational article. A lot of speculation, some ignorant rambling (nobody at The Atlantic seems to know where electrical power on a plane actually comes from), and a lot of misplaced vitriol. You'd think people would be grateful that airlines are offering standard electric outlets on the plane at all.

http://www.smbc-comics.com/index.php?db=comics&id=2035#c...

Every pacific crossing I've been on in the last three years (all 747s) has had AC to my seat. As far as I could tell all the seats had it. Large jets have auxiliary engines that power the coffee makers, the ovens they use for cooking in the plane, the lights, etc. You can normally see the exhaust for this engine on the very tip of the tail.

Someone please correct me if I'm wrong, but I believe this article is defeated by the actual fact of the matter that some planes do have AC to all the seats.

The APU doesn't run in-flight (unless shit gets real and the engines are disabled or need to be re-started). Everything electric pretty much runs off the generators powered by the main engine (in-flight), or ground power (at the gate).

Having outlets at all the seats isn't the same thing as having a large number of them drawing power at the same time.

Nobody needs 120v AC -- everyone on a plane is stepping it down and converting it to dc! The solution here isn't 120vac to every seat -- it's coming up with a new DC standard that plugs directly to our devices. The hard work of an airplane based inverter is undone by our power bricks, and energy is lost to heat in both. Lots of industry cooperation needed for this to happen, though.

That industry standard DC supply is 5V from the USB port. Stick a USB port in the arm of each seat and sell an adapter kit for common laptops and phones on-board. Although i'm not sure a USB port will supply enough current for a laptop.

It won't. The solution is to force everyone to use the 'car' (or cigarette lighter) variant of their chargers.

Makes you wonder how they even manage to power those 500 Watt aircraft headlight bulbs, tens of KW in avionics, coffee machines and kettles, ovens, in-flight entertainment system per every seat etc etc

The reason none of those are a problem is pretty straight forward. Each of those systems were designed to be powered by the aircraft's gen-sets, rather than the other way around.

When designing an aircraft and its sub-systems, the engineer provides power availability specifications. The people who make the headlights, avionics, and coffee machines are all aware of the common power configurations and design their equipment to work with that specification directly. I used to work on light aircraft (private), which all used 24 VDC. Everything in the plane was designed to run on 24 VDC. Commercial airliners likely have more than one voltage specification available, but I'd imagine it's all DC.

Any time you have to convert voltage, you're going to lose some efficiency. Inverters (DC to AC) have some particularly nasty characteristics that make them undesirable on an aircraft. A DC voltage converter would work, but you still introduce some degree of inefficiency. A good switching DC voltage converter can exceed 90% efficiency, but so can an AC inverter. Neither operates at that efficiency all the time though. I know that AC inverters perform best when run at close to nominal load. At lower current levels, efficiency drops. I don't know enough about DC converters to say.

Add to this the fact that inverters and converters are heavy, and you can begin to understand why a power outlet at each seat is problematic.

I took 737 mini (two day) ground school about 10 years ago. I believe the commercial jets' main electrical buses are 3-phase 110/200 volt 400Hz AC, created by the starter-generators on the turbines. It's relatively straightforward to tap across two of the terminals and get 110VAC, but it'll be at 400Hz, meaning not everything designed for 110VAC/60Hz will be able to handle it.

(Also, some older private aircraft, such as mine, use a 12VDC standard.)

Because a) they know at the time the plane is designed the exact power draw of all those bits of kit and b) said bits of kit can be designed from the ground up to play nicely with aircraft power supplies.

Boeing 747 was designed in 1960s.

Yes and no. The 747 is still in production and has been revised many times since. A 747 bought today will have relatively little in common with one bought in 1970.

It is still roughly the same energy requirements to lift one in the air and keep it there. Electricity intake is a tiny part of that.

Yes there was no in-flight entertainment in mid-60s, but avionics back then were still to a great extent valve-based and consumed gobs of power.

It's not just the power - it's the weight of the transformer, inverter, etc.

Since every laptop has a battery, you could do "rolling blackouts". The laptop doesn't need power the whole flight. I know from going to conferences sometimes just plugging in once in the middle of the day allowed me to make it without being plugged in for the rest of the day.

You might have failed to consider conservation of energy here. The laptops use a steady amount of energy whether plugged in or not (more or less), and if they're unplugged for a while, then they'll draw more power during the time they are plugged in as they recharge their batteries. In fact, if the batteries are not perfectly efficient and thus don't provide the same energy that was used to charge them, you're now using more energy per time by running it through the batteries first.

Of course, doing the rolling blackouts might encourage less use of devices, reducing power use.

Actually, in OS X my laptop will use less power when on battery power. The clock speed goes down, the display dims, the hard drive goes to sleep faster, the display adapter switches to the less powerful one.

That's a good point; it might well outweigh the battery inefficiency's increase in power use.

I think airlines could pre-wire all seats to be able to provide 110v supply if purchased with your ticket or on-board as an add-on. Then have an intelligent switcher, which only energizes the socket if they have been pre-purchased, reducing the need to distribute live power around the plane.

Most people would really only want a few hours of charging. Then you could have a capped number of active sockets per flight of say 50-100 seats.

Interesting article, but a whopping quarter of kilowatt to every seat? Isn't that a bit overkill? Assuming that typical laptop charger drinks 80 joules of energy per second at most, and since laptops luckily have built-in energy sources for couple of hours, the power output could be time-divided, eg. every output is powered half of the time in 30 minute intervals. Assuming not everyone needs power at all, two power outputs per three seats should be enough. Suddenly we have reduced the needed peak power to 1/9th of the original!

The OEM DC adapters for Apple laptops prevent battery charging, because some in-seat DC outlets don't provide that much power.

I've had trouble connecting a laptop that wants to charge to inverters before, so this isn't without reason.

http://www.seatguru.com/articles/in-seat_laptop_power.php

For those advocating for a low-voltage DC power source, look at Empower--it's installed on more than 40 airlines. 15V DC, 75W.

http://en.wikipedia.org/wiki/EmPower_%28aircraft_power_adapt...

For anyone who was wondering over a 12 hour flight the fuel cost would be aproximatly:

(240 watt) * 12 hour * 500 people / 45 MJ (energy dencity per gallon) / .35 energy effecency = 330 gallons * 6.8 lb / gallion = ~2244 pounds. Granted this is probably +/- 30% depending on the fuel, engine effecency, transmission losses etc.

For comparison a 12 hour flight would burn ~ 43,000 gallons or 292,000 lb of fuel.

Given that, in most overseas flights, sufficient voltage is available at every seat to power in-flight entertainment, I wonder if it's an easier engineering problem to have a 15-20 volt outlet instead (though I'm not sure if there's enough juice for the extra 2-3A).

True, not laptops have the same AC plug, so an adapter would be necessary.

Not necessarily. Some sockets can cope with the majority of the AC plugs in Europe and America.

http://img.hisupplier.com/var/userImages/old/selong/selong$7...

That's similar to what Air Canada had on the seat back for the flight I took SYD<->YVR (economy). My Australian laptop plug worked fine with it.

So it's definitely doable, and I'd be prepared to bet money that it runs off the same APU that powers the entertainment system.

Even though the articles claims that its a worst case scenario, most people on an airplane wouldn't use their 19", 8kg über-gaming laptop. Most people would probably use more portable versions, ending up in a avarage effect that is way, way below 220W.

If 110V is not feasible, can we try lower voltage? 36V DC is sufficient for laptops with correct adapters.

Also I don't really want to work on laptops in tight space anyway. A 5V USB port is sufficient. All Air Canada flights have this. (Due to RIM I guess?)

There is nothing wrong with the voltage (110vAC), the issue is power... and to achieve a given power amount (70W typically for laptops), lower voltage requires higher current. See my comment under the 12vDC lighter plug suggestion http://news.ycombinator.com/item?id=1828197.

36vDC would have similar weight problems and, in addition, would require everybody to buy and haul around Yet Another Power Brick since it is oddball.

Ah, thanks for clearing it up! Another question: I saw many international flights feature a VOD system with a LCD screen that is playing some movies on the back of every seat. Does the power to drive the system enough to charge a laptop then?

I am not familiar with the VOD systems, but I really doubt it. A typical laptop brick is rated at 70W and it probably pulls close to that with a discharged battery.

I would expect the VOD display system to be running around 10W. My guess is 1W lost in a 90% efficiency power supply, 5W for the display, 1W for an ARM processor, the rest for the video decoder chip and miscellaneous support chips.

All the Air Canada flights I've flown from YVR have a 110 plug too. I've no idea what the voltage/current actually is, but it charges my laptop just fine. (There's generally only one plug for every 2 or 3 seats though.)

They already have 400hz power (not sure of the voltage) from the engines.

Why not just use a switching power supply to change that to 60hz 110v? Why this whole business with inverters?

There may also be concerns about insulating the flight electrical system from the cabin electrical system. What if there's a surge or huge load in the cabin? You need to be sure that that sort of thing can't affect the engine operation. The easiest way to be sure is to put an air gap between them.

They already tell you to turn off your Gameboy. I doubt they'd let passengers get anywhere near plugging directly into the power from the engines.

They could run a generator off a turbine in the airstream. A lot of EW pods were powered this way. This would cost a bit of fuel, but there would be no direct connection between the cabin electrical system and the engines.

Switch-mode power supplies are essentially DC rectifiers, which will never ever give you 110V, 60Hz (an AC voltage).

One way to change the frequency of a power source is through a double-conversion type AC/AC converter, i.e. 1st stage is a rectifier which outputs a DC voltage - this is an arbitrary DC voltage, but it needs to be within the voltage tolerances of the 2nd stage - an inverter, which reconstructs an AC voltage from the DC link to whatever frequency you like.

This setup is also the basis of most UPS systems btw, with a battery connected in the DC link.

A switch mode power supply can do a whole lot more than act as a rectifier. "Switch mode" refers to the turning on and off of numerous silicon switches usually connected to some kind of LC energy storage/filter, and this is the basis of modern rectifiers, inverters, step-up and step-down converters, etc.

It is in fact possible to use a switching circuit to convert an arbitrary ac voltage/frequency to another arbitrary ac voltage/frequency directly without a DC link intermediary. This is called a "matrix converter." http://en.wikipedia.org/wiki/AC/AC_converter

So it should theoretically be possible to take say 200VAC at 400 Hz and convert this to 120VAC 60Hz. In fact this would probably be more compact/less expensive than the usual inverters mentioned in this article, since these are usually meant to be powered by a low voltage DC source and thus have to deal with taking a low voltage and very high current and first stepping this up to several hundred volts, then modulate it into an AC sine wave. A matrix converter (or even AC-DC-AC converter) would have no such requirement if it were powered from the already high voltage aircraft power bus.

At this point I think it's a matter of the technology catching up, since this is a highly specialized application that has just recently become an opportunity for innovation.

EDIT: Also - 240W per person? This seems outrageously high as a baseline load. I would estimate more like 50-100W per person on average, with 300W peak (like when the power supply is first plugged in.) The peak loads would not all happen at once unless everyone decides to plug in and turn on their computers at once, in which case the power limiting would kick in...

Fair enough, although I've never actually seen an AC/AC converter without a DC link in real life (the closest thing probably being a direct torque control VSD).

The difficulty is that everyone wants it yet no one wants to pay for it. (I'm sure it works quite fine in first class)

So, why not cigarette adapter DC sockets?

Power is voltage times current. If you supply 12vDC instead of 120vAC (1/10 the voltage), you need to supply 10x the current for the same amount of power.

To supply 10x the current, you need substantially larger wires. Wires are heavy. Airlines don't like heavy, it costs a lot of money over the lifetime of an aircraft to haul non-fare paying weight around.

Another point, 12vDC is not a typical aircraft voltage, so a DC-DC converter would be needed to generate the 12vDC. 12vDC is typically not a native laptop input voltage (19vDC is more typical), so another DC-DC converter would be needed. At that point, an inverter (DC-AC) and normal laptop power supply (AC-DC switcher) makes more sense (efficiencies are similar).

Because somebody would plug in something dangerous. Believe me there would be some genius with a George Forman plugin grill or similar.

There are DC adapter plugins in aircraft - the idea is that they are only sold for laptops and are expensive enough that few people use the.

Not true at all. Every American Airlines airplane has DC power that is provided via a cigarette-lighter socket. It works quite well with an inverter and a standard power brick, or a special DC/DC converter.

I don't use it very often because all the cords that it would require annoys me, and my laptop has 12 hours of battery life. But it is there, leading me to believe that this is not actually a problem.

(I think the fact that it's DC power limits the number of people that will use it, because you have to plan ahead, and nobody ever plans ahead for flights except seasoned travelers. If it was AC power, people would plug stuff in just for the hell of it, instead of reading a book as they do now.)

It would appear to me that most of the stupid stuff you could plug into a cigarette lighter pales in comparison to the stupid stuff that you can plug into a 120V AC. (eg. You're more likely to find a 120V AC plug on the aforementioned George Foreman grill)

Perhaps this would be (or would be posed as) a security problem, too.

I am not familiar with any specific methods of causing a large explosion that access to a 120V AC socket would allow, which not having access to one would not, with what is currently allowed to passengers through airport security [0]; But considering that producing a cigarette lighter or some nail polish remover in the cabin are grounds to be tackled by an air marshal and prosecuted, an electrical outlet is a hell of a lot of accessible power.

  [0] kindly disregard my past five minutes' search history, NSA sniffer

Yep. And this is the reason that all the sockets have built-in current protection. Additionally, there are circuit breakers per seat row, which is what I discovered when I tried plugging in my 110W laptop power adapter into one of them. The other passengers on the seat row were not happy when the flight attendant said that they were not allowed to reset the breakers. Another lesson learnt - bring a lower power adapter. :(

yes - I think thats the main objection to fitting 120VAC, the thought of an entire flight of teenage girls with hairdryers.

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