Why are laptop power cords so heavy?

October 11, 2005 11:11 PM

Why are laptop AC adaptors so damn heavy? Do they make lighter ones?

I have a 2004 IBM ThinkPad T41 which I take with me all over the place. The latop itself isn't too heavy but adding that to my books and then the power cord really starts to weigh me down. Do I have any other options? Would I be better off carrying around an extra battery?

posted by radioamy to Computers & Internet (10 answers total)

If you're just carrying to and fro work or school, then you might just buy another charger. The real deal is $50, and the knockoffs are $10.

Here you go, matey
As far as I know, they're all the same, more or less.

Now I'm going to buy one.
posted by metaculpa at 11:35 PM on October 11, 2005

A smaller charger wouldn't produce enough current to run the laptop and also charge the battery. You could play around with various potentially lighter models, but it won't be worth the effort.

I expect metaculpa is right about them being 'all the same'. If there are quality differences the odds of damaging the laptop are very very small, so at worst you are only risking the $10.
posted by Chuckles at 11:48 PM on October 11, 2005

My rudimentary electric knowledge tells me that they are heavy because, to convert AC to DC, they generally have a set of coils in them, which are invariable heavy.
posted by teece at 11:58 PM on October 11, 2005

Kensington make after-market chargers which seem to be both lighter and more versatile than the one which comes with a laptop as standard. They just cost more, which pretty much answers your question, I would say.
posted by AmbroseChapel at 12:28 AM on October 12, 2005

They're heavy so that they can advertise their laptops as being that much lighter, to answer your question.
posted by softlord at 12:52 AM on October 12, 2005

My rudimentary electric knowledge tells me that they are heavy because, to convert AC to DC, they generally have a set of coils in them, which are invariable heavy.

The coil (transformer) is for reducing the voltage, not for converting AC to DC.

Laptops draw quite a bit of power and thus their adapters must be beefier than the wall warts you use with your Discman.

That said, if you have a Mac laptop, check out Madsonline for small adapters. One of their Powerbook adapters even has USB and FireWire ports for charging devices that can be charged that way.
posted by kindall at 1:20 AM on October 12, 2005

the adapter for the mac mini is almost the same size as the computer itself - i suspect the hard drive is actually placed in the power adapter - though i have no proof
posted by FidelDonson at 2:38 AM on October 12, 2005

Computer power supplies are switchmode - they rectify the mains to high voltage DC and then rapidly (tens of kHz) switch that on and off across an inductor. By controlling the switching duty cycle & frequency, they regulate the output voltage and current, giving clean power for the computer.

For safety reasons (isolation), in reality they use a transformer in place of the inductor; a transformer is just an inductor with multiple windings that are connected by the magnetic flux through them. The mains and switching is on one winding, the low-voltage, high current output is the other winding and there is no electrical connection between them.

The large mass is mostly due to the iron core in the transformer. The more current you want to put through the transformer, the larger cross-sectional area the core needs to prevent saturation. Computers use a lot of current so the transformer cores are quite large and heavy.

Laptop power supplies are also complicated by the fact that they usually work with input voltage anywhere between 100V and 250V; such a design will be heavier than one that works only for a small range of input voltages, eg as seen in a PC.

Fidelson: no, the mac mini hard drive is in the main box, but (I think) they're a 2.5" laptop drive rather than a 3.5" normal size one. You can tell this because there is no data cable between the power supply and main box.
posted by polyglot at 6:02 AM on October 12, 2005

IBM/Lenovo does sell an ultraportable charger. It weighs 8.5 oz rather than 12. I think your books are much heavier.

The Mac mini adapter is kind of silly large, considering they could have just used a Powerbook adapter (which is smaller).
posted by smackfu at 6:42 AM on October 12, 2005

smackfu links to a 56W charger, while a 72W charger comes standard on all but the X series laptops.
posted by Kwantsar at 8:11 AM on October 12, 2005