Does it matter how efficient it is? Voltage from the battery will vary from 12.2v - 14.8v with the car off and battery partially discharged to the car running. He could use a voltage doubler and a regulator to get whatever voltage he needed. Check the output from an 18v charger, it'll probably be around 22v open circuit. Or he could build a SMPS if he wanted to get fancy.
It'd be easier to just use a cheap inverter, don't need much for a laptop.. and it has other potential uses. He'd increase overall power efficiency by using an Atom powered netbook and keeping the screen dimmed more than he ever could by having an efficient power conversion and charging system. Using 2 smaller 12V batteries or 4 6V batteries with a regulator would be easy and fairly efficient depending on needed charge voltage. THE most efficient way would be to make battery charge packs from 6/9/1.5V batteries. 1.5v cells gives you the most variability. Just wire up as many in series as you need to get the charge into the laptop.. then the only loss you have is the energy wasted actually charging the battery. Makes more sense to just carry an extra laptop battery, though. Does he plan on carrying the battery? Is he going to be using a vehicle to charge from? How long does the laptop need to run? How big is the battery he intends on using? What's his absolute goal? Does the laptop need to remain portable or can he just wire up a large battery, taking the place of the laptop battery? Why an older laptop? They tend to be pretty inefficient. -Frank From: Sean Swehla Sent: Tuesday, June 01, 2010 11:49 AM To: [email protected] Subject: Re: [mhvlug] DCtoDC or DCtoAC for Laptop? On Tue, Jun 1, 2010 at 8:48 AM, Sean Dague <[email protected]> wrote: On 06/01/2010 04:16 AM, WestHurley ComputerReCycling wrote: > A friend is planning a field trip with an older Laptop. He wants to run > this Laptop and charge its battery from a 12V auto battery. > > As a result, he was wondering what is more efficient for this a DC to DC > Converter or a DC to AC Inverter? In general, just changing Voltage on DC is going to be far more efficient than generating alternating current, then converting that back to DC. You loose a lot of power to heat and EM in the DC -> AC, AC -> DC process. Contrariwise, it'll most likely be easiest/cheapest to get the gadgets you need to do DC->AC->DC. I was looking into this not that long ago, and the DC->DC options were rare and expensive. If you're willing and able to go the diy route, I'd certainly recommend a flyback or boost converter. Otherwise an off-the-shelf inverter and your charger are probably the best bet. /thor -------------------------------------------------------------------------------- _______________________________________________ Mid-Hudson Valley Linux Users Group http://mhvlug.org http://mhvlug.org/cgi-bin/mailman/listinfo/mhvlug Upcoming Meetings (6pm - 8pm) MHVLS Auditorium Jun 2 - Android Jul 7 - Patent Absurdity - The Movie Aug 4 - Samba
_______________________________________________ Mid-Hudson Valley Linux Users Group http://mhvlug.org http://mhvlug.org/cgi-bin/mailman/listinfo/mhvlug Upcoming Meetings (6pm - 8pm) MHVLS Auditorium Jun 2 - Android Jul 7 - Patent Absurdity - The Movie Aug 4 - Samba
