XPost: alt.home.repair   
   From: kludge@panix.com   
      
   Mark Olson   wrote:   
   >In rec.autos.tech Smoke Signals  wrote:   
   >>   
   >> I have a charger for my Lenovo laptop that plugs into 12 V cigarette   
   >> lighter socket, so theoretically less losses than converting to AC and   
   >> back to DC.   
   >   
   >That car charger will certainly be more efficient than plugging   
   >the laptop's mains power brick into a 12VDC to 120VAC inverter,   
   >but it is still converting the 12VDC to an AC current internally,   
   >as a necessary step in the 12V->20V DC->DC boost conversion.   
      
   Yes, and such devices are also more convenient, and they are available   
   from most laptop manufacturers or worst-case from a third party.   
      
   If you have a moderately-sized laptop pulling 50 watts and you have a   
   car battery able to put out 40Ah or so before dying, then you have a   
   continuous battery load of 4 amps and can run the laptop for about 10   
   hours.   
      
   Car batteries are starting batteries and they are designed for high   
   peak currents rather than the ability to be discharged very far.  They   
   usually have very thin plates in order to get more plates with more   
   surface area for the high starting current, so they are prone to issues   
   with the plates warping when discharged a lot.  So don't discharge the   
   car battery down too far.  40Ah is not out of the question but don't   
   treat it like a telco battery.   
   --scott   
   --   
   "C'est un Nagra. C'est suisse, et tres, tres precis."   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)