[TriLUG] OT: battery charger voltages - using 18V charger on 16Vsystem

[Brian Henning]

I can address the question of why you use a 16-volt charger to charge a 
9-volt battery (at least, I think I can)..
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" <mack.joseph at epa.gov>
To: "Triangle Linux Users Group discussion list" <trilug at trilug.org>
Cc: <jmack at wm7d.net>
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 - smith.johnb at epa.gov
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