I keep all of my miscellaneous cords and cables together in a small vinyl bag. Some of them - my cell phone chargers for example are single piece affairs. At one end is the AC plug, there’s some sort of boxy unit, and out the other end of that box comes the plug that fits into the phone.
My Nikon camera has an AC cable, and a box-ish thing that holds the battery once removed from the computer. The box and the cable are two pieces.
My wife’s Dell laptop has a single piece charger. AC cable, leading to the ubiquitous ‘box’ and from the end of that, the cord that plugs into her laptop.
My Toshiba has an AC cord, with a plug that fits into a socket on the second cable - which has the boc, and a smaller cable that plugs into the cable.
WHY??
Why are these all different configurations? Is there some technical standard that determines that certain devices need separate pieces? Why can’t single piece converters be used everywhere - not necessarily a “master” charger, I know that’s not possible, but what IS the reason for two separate parts?
And don’t even get me started on the POS Apple thing that comes apart like a Lego toy, dies after a year, costs $150, and that they never have in the store, so you have to wait 3 weeks for it to show up at your door.
I suspect it’s cheaper to build the power supply (box) to accept a standard AC cable. Buying an AC cable costs, say, .50 while molding a cable to the box costs .60. Sell 100,000 laptops and you make $10,000.
All of the laptop power adapters at my job (we’ve used both Dells and HP/Compaq for many years) are two-piece models as well. I always thought it was for ease of manufacturing - you can make all of the transformers (the box) to whatever voltage and current you require for your various models and countries, changing them from year to year as you introduce new laptops, however at least one part (the power cord) doesn’t have to change at all. It may seem like a small thing but if you can just buy a million of them upfront and never have to alter that part of the design it could add up.
Oh, you can also make the power cords with different plugs on the end so that you don’t have to build two completely different power adapters just because Country A and Country B have different wall plates.
From an IT perspective it comes in handy once in a while when somebody manages to damage the power cord, it’s easy to just swap that bit out (I’m sure that’s not why they are built that way, though).
The kind where there’s a box with a separate mains cord are made that way so that they can be sold into different markets with different kinds of mains outlets by just swapping out the mains cable that runs from the wall to the transformer box.
Some smaller mains adaptors for mobile phones and PDAs sometimes have a wall-wart type PSU onto which an appropriate plug clips directly, but that means the manufacturer has to make the plugs specially, whereas the cables that run from the mains socket to the laptop PSU box are usually a standard configuration that is already on the market (usually a three pin ‘kettle’, or a two pin ‘figure 8’ connector).
Maybe the AC wire feeds the battery pack’s charger (national voltage/cycle differences meaning it charges a little faster or slower) while the battery pack itself has the smart circuitry needed to output to the system at the right operating characteristics?
Most laptop PSUs (actually most PSUs or power adaptors) are switchmode now. No transformer as most people think about. Switchmode PSUs can be designed to accept a broad range of input voltage and frequencies. You’ll see on them 100-240V, 45-65 Hz or so. Switchmode means they rectify the mains to DC, then use a fast switching frequency (~50kHz) to supply the output voltage, varying the pulsewidth to maintain the correct output voltage.
The guts of the “box” in the middle of a laptop power cord are able to absorb any commercially standard voltage & frequency & serve up the right kind of juice to the laptop at the other end. They even work with the 400 Hz power common on aircraft & ships.
There’s only one transformer primary & no mechanical switching is used.
Crudely stated, they take whatever kind of power comes in, smash it down to low voltage DC then use that to power an oscillator to produce low voltage AC of the desired frequency. That’s what come out the other end & goes into the laptop.
Wiki or howstuffworks.com on “switching power supply” will have more.
Mine actually came with three cords, providing UK, American and European plugs. Much more useful than messing around with travel adaptors.
I’ve also had a mobile phone adaptor in the past which, while being a single plug-mounted unit, had a prong section which slid out and obviously could be replaced in the factory (or elsewhere) with another regional version for minimal cost or effort.
Haven’t switching power supplies been ubiquitous for ages now? It seems like it was a long time ago when we had those old transformers. I seem to think my Amiga 500 even had a switching power supply, in that it was the same size as that on my C=128, but light as a feather.
I would think part of the reason is you need a transformer of some sort, you have one of 3 places to put it:
1 Inside the laptop, which would add bulk, weight and heat
2 at the plugin end, which would limit where you could plug it in, much like the ‘wallwart’ transformers on other AC to DC adapters, being so big that they block some other outlets on a powerstrip(and laptop transformers are rather large.
3 in the middle where everyone will be happy unless you wonder why it’s there.
I don’t know - the last few laptops I’ve bought had a PSU that was about 6 inches by 3 by 1, heavy, and gets hot - I don’t think these were switched mode PSUs - they were all budget machines though - maybe the higher spec and branded ones use better.
Not sure it’s a reason, exactly, but the two-piece cords mean you don’t have to drill such a large hole in a piece of furniture when running cords through shelves or panels.
Now that you mention it, although I hate my work Dell, I do enjoy the fact that it has the two piece power cord. The 120VAC portion stays nicely tucked behind the desk and cubicle wall (this was 15 minute, sweaty, painful job), and I can just grab the inverter and take it home with me, where at home I have (for some explained reason) quite a surplus of those 120VAC portions.
