Laptop external power from batteries (DC/DC)

[michael miller]

19.5v is only used for charging.  The internal battery nominal voltage
is 14.4 (4 x 3.6v cells in series).  Li, NiCd and NiMH batteries tend to
maintain a nearly constant voltage until they are almost fully
discharged at which point voltage drops rapidly.  Lead acid battery
voltage tends to drop continuously from full charge to full discharge.

Mike Miller
On Wed, 2008-08-20 at 20:03 -0400, Bill McGonigle wrote:
> On Aug 20, 2008, at 14:58, mike ledoux wrote:
> 
> > A good (and sadly, expensive) DC-DC voltage
> > converter is only about 85% efficient, so to get the 19.5Vdc @ 4.62A
> > you need, you will draw ~8.63A @ 12Vdc.  ~5 hours becomes ~4.5.
> 
> Yeah, that does sound a bit wasteful if one is starting from scratch.
> 
> OK, so how about hooking up a 1.5V a 6V and a 12V deep cycle battery  
> in series?  Assuming one could find cells of comparable AH ratings.
> 
> Or, if one were more serious... IIRC the last time I looked inside a  
> battery it was made of several plates lined up together in a row,  
> sitting in an acid bath.  Actually, alternating repetitions of  
> different kinds of plates, which I assume were cells of some voltage  
> in series.  So, if one bought two marine batteries, a bigger box, and  
> was familiar with proper acid handling techniques, ought there be an  
> electrical reason that 'just' making a 19.5v battery with the  
> required number of cells would be insufficient to power a laptop  
> (finding a charger might would be a separate challenge)?  I'm curious  
> if the voltage drops as the battery discharges or remains fairly  
> level.  Come to think of it, laptop battery voltages aren't 100%  
> level, so I wonder how precise that 19.5V really needs to be (12V and  
> 6V are easily sourced, for instance).
> 
> Also I've noticed that many laptop vendors offer a 15.5v adapter to  
> be used on airlines, which have some sort of under-seat connectors.   
> These power the laptops but not the laptop's chargers.  So there are  
> probably extra pins or smart power control board to factor in.
> 
> I think the new answer to "what can I do with my old obsolete  
> laptop?" is "give it to somebody playing with batteries". :)
> 
> -Bill
> 
> -----
> Bill McGonigle, Owner           Work: 603.448.4440
> BFC Computing, LLC              Home: 603.448.1668
> bill at bfccomputing.com		Cell: 603.252.2606
> http://www.bfccomputing.com/    Page: 603.442.1833
> Blog: http://blog.bfccomputing.com/
> VCard: http://bfccomputing.com/vcard/bill.vcf
> 
> 
> _______________________________________________
> gnhlug-discuss mailing list
> gnhlug-discuss at mail.gnhlug.org
> http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss/
-- 
michael miller <k4ghp at comcast.net>