Maximum Wattage of Power Points??
 

I have an HP laptop with the i720 processor. Because of this, it comes with a 120 watt power supply.

I recently flew a SQ A380 flight, biz class from SIN to MEL. When I plugged in, the power dropped off, as though tripping a circuit breaker. This same phenomenon occurred when tested on several other seats.

Coming back, I rode a SQ 747, top cabin. The same thing occurred.

What is the max allowed power draw on these power points? I want to buy a smaller power supply, just under the limit.

TIA

You might be better posting this in the Tech Log Forum

Alternatively a search on Google may be fruitful. There seem to be quite a few sites and forums which talk about these things. You may not even need to go past the first site offered.

FOR

120W is pretty damn chunky for a laptop. Most Dells will run on 65W although a few are 90W for charging and 65W for running without charging. I've yet to see a 120W PSU for a lappie, but then again with the current climate I rarely see people speccing i7s for laptops.

I do know there's a maximum draw in planes though, as this was explained in the inflight guide on a plane I was in recently. I can't remember what it was, but it was certainly less than 3 figures.

the adapter uses 12 volts to power it, so with 120 watts, its drawing 10 amps. that is a fair whack. I guess the cct breaker wasnt that big. Mind you , a 120 watt load is pretty heavy for a laptop, should only get close to that if the battery is dead flat, the fan is running flat out and you are doing very system intensive stuff.

Note

The OP says that his laptop comes with a 120W power supply. That does not mean it will draw the full 120W as I think the power supply will be "over rated" so it doesn't run at the full maximum rating.

Even so, you would have to be doing some pretty intensive stuff to use that sort of power in the first case, and I can't see him rendering 3D images in-flight.

If you google 'HP laptop (model number) +specifications' you will be able to find out what the current draw is.

In an ideal world. In my experience just powerful enough keeps manufacturing costs down. I had a problem with a pal's desktop where he had a succession of faulty HDDs. It turned out his upgrade to a larger and faster HDD increased the power requirement by a small amount which overloaded the puny power supply which was only just adequate for the original specification. There was nothing wrong with the HDDs!

My brother had a problem with his very powerful laptop overloading the seat power supply on his trips to the USA. He resolved it by buying another less power hungry machine for use when flying.

The in seat DC supplies are limited to 75W, I don't know about the ones that have 110Vac at the seat, but I would imagine the limit is similar if not the same.

The PSU for the HP is probably overrated, it will have enough to run the laptop (say 70W), but to charge the battery whilst running (say another 20W) plus enough to power attached devices (USB x4 at 5W each). So 120W isn't too surprising. The laptop probably averages much less than that in normal usage, probably down nearer 30 to 40W, but the problem with laptop PSUs, especially nice chunky 120W ones, is the "Inrush" or "Surge" current. This is the very high current that occurs when the PSU is plugged in. It only lasts a few milliseconds, but is often enough to trip circuit breakers, which is why "Slo-Blow" fuses exist.

Sometimes this can be overcome by plugging in, and reseting the breaker quickly as soon as it trips. I.e. Using the short time before the breaker trips to supply the inrush current. Whether or not you could get cabin staff to do such a thing is another question.

plug in with the m/c off let it charge the battery for a while then start it up that should get over the surge problem

On the (almost exclusively BA) flights I've been on, it's noted that the power jacks cannot be used for charging (it asks you not to). Somehow they manage to enforce this - I have no idea how! Two laptops I've used on planes didn't charge from a medium battery level when they were plugged in there.

120w sounds like a bit much for an at seat jack. I'd agree that you are better posting in tech log however with the profusion of different seats and so forth you may get a few different answers. That said, perhaps there's a common standard or something. :cool:

Some good answers above.

What really worries me is that the OP proposes using a smaller power supply as a solution to the problem. This won't work. The computer will try to take the same power and the weaker supply will try to produce that power and will fail. You will know when it has failed by the burning odour, smoke, flames, explosion and fuslage rupture, followed by a calm weightless feeling as you achieve -9.81m/s2 vertical acceleration. Some time later you may briefly notice a splash or thump.

Never, never, never use anything but the correct supply from the original manufacturer.

Yes.....and no.

As I mentioned, Dell are pretty good in that their earlier 65W PSUs will power a laptop that comes with a 90W PSU but won't attempt to charge the battery at the same time.

Incidentally, the first link in FOR's Google search has a lot of useful info (that 110V @ 75W is the norm for planes).

Don't understand that. The link from charger to laptop has two wires, just power. No way of telling the laptop what type of charger is in use.

They manage it with the Apple PSUs somehow.

The airline DC adapter is set to output a specific voltage that tells the Mac to not charge the battery.

The proper PSUs step the voltage up and down depending on the current load from the laptop. This is what alters the green/orange LED in the adapter plug. When the laptop is charging the battery the current is higher, the PSU steps up the voltage ad turns the orange LED on. When charging has finished the curtsy draw goes down, the PSU steps the voltage down, which turs out orange LED and lights the green one.

So with only two wires it is possible for the laptop and PSU to alter their behaviour I response to each other.

I find that tale very hard to believe. But then anything Apple is hard to believe.

I had a look at some nerd blog posts and found some relevant information. Apparently there are some laptop chargers (and these must be used with the correct laptops) that have a concentric three wire connection. Two wires are used for power and a third wire is for telling the laptop whether or not to charge its battery. Mention is made of HP and Dell using third-wire signalling, and availability of special power units for air travel use.

This is very different from the OP, who proposes using the wrong charger. I cannot say too often always use the charger provided by the original manufacturer for your laptop.