When you charge an iPhone, you can use a small white cube to convert 110V AC to whatever it is the iPhone needs. When you charge a laptop, you need a “power supply”–generally a much larger brick–to do something similar. Why?
December 27, 2009
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USB provides 5v and 500mA, where your typical laptop brick is around 12-20v and 15A.
While I’m sure you could wire it up, charging your laptop via USB would likely be an all-day event.
Comment by Andrew Forman — December 31, 2009 @ 11:54 am UTC
From Steven on Facebook:
Comment by adam — December 31, 2009 @ 6:49 pm UTC
Most modern PSUs (notebook bricks, cellphone chargers and desktop internal supplies) are switched mode, so don’t have any transformers. Normally the only coils are in the output regulator.
http://en.wikipedia.org/wiki/Switched-mode_power_supply
Strictly speaking the supply doesn’t push current, but the load draws it.
This means that you’re safe if the load draws less current than the PSU’s rated maximum, but it may blow it if you try to draw more. This can be spectacular and very smelly. Don’t ask how I know.
Loosely speaking, watts = volts x amps.
Also, if the output voltage of your little white cube (5 V, say) is less than the voltage required by the notebook’s charging circuitry (around 15 V for my Toshiba) nothing will happen or, at worst, the battery (rated at 10.8 V for the Toshiba) will try to discharge through the charger unless there is something (e.g., a diode) to prevent this.
Comment by Graeme — January 19, 2010 @ 11:32 pm UTC