Same reason the nominal charging voltage of your car (12-volt battery) is also around 16-18 volts. The short, electrical-theory-free answer is a higher charging voltage means a shorter charge time.
The slightly longer, gloss-over-the-details answer is that at a higher charging voltage (and therefore higher charging current assuming a simple RC charging circuit), it takes fewer multiples of the RC time constant to reach the target voltage across the battery.
The warning against using a higher-voltage supply is to protect you from potentially blowing the regulator circuits that drop the 16V down to the various lower voltages used by the computer's circuits, and possibly to limit the charging current through the battery. (Higher current == faster charging... too high current == bang) You would *probably* be safe only two or three volts over, and suffer little more than shortened regulator and battery life, but I would strongly suggest sticking to the specified ratings.
Cheers, ~Brian
----- Original Message ----- From: "Joseph Mack" <[EMAIL PROTECTED]>
To: "Triangle Linux Users Group discussion list" <[EMAIL PROTECTED]>
Cc: <[EMAIL PROTECTED]>
Sent: Tuesday, November 02, 2004 9:40 AM
Subject: [TriLUG] OT: battery charger voltages - using 18V charger on 16Vsystem
I have an IBM thinkpad with a 9 cell (nominal 10.8V) Li-ion battery. The charger is nominally 16.8V charger (measured 16.0V).
(Anyone know why you charge a 10.8V battery with a 16V charger? Surely the internal impedance of the charger can't be that high.)
I also have available a Toshiba charger with the same plugs, except that it is a 18V charger (nominal and measured).
Does anyone know if you can use an 18V charger in place of a 16V charger?
Searches with google for battery/battery charger specs haven't been real helpful. I did find
http://www.bixnet.com/unpowbat.html
which has a dual voltage 19/16V charger which they say to set to either 16V
or 19V according to the system you're charging. They don't say that you'll blow
your system if you use 19V when charging a 16V system.
Thanks Joe
--
Joseph Mack PhD, High Performance Computing & Scientific Visualization
LMIT, Supporting the EPA Research Triangle Park, NC 919-541-0007
Federal Contact - John B. Smith 919-541-1087 - [EMAIL PROTECTED]
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