On 2014-11-25 18:48, John Andersen wrote:
You can power a 19 volt laptop from 2 car batteries for many days on end. All you need is a LM7809, which will set you back $1.95 plus shipping.
You gotta be kidding. That thing is rated at 1A, a serial voltage regulator. 27 volts on the outside (real battery voltage is 13.6), 19 on the inside, meaning 8 volts voltage drop. At 1A that's... wait. A 7809 gives 9 volts. A laptop needs 19! The closest is the 7818. http://pdf1.alldatasheet.com/datasheet-pdf/view/173537/UTC/LM7818-TA3-G-T.ht... Ok, 18 volts on the inside, 9 volt drop, 9 W waste, 18W supplied. Only 1 A available, with a good heat sink. Not enough. My laptop needs 3.5. No. These things are done with switching regulators for a reason. -- Cheers / Saludos, Carlos E. R. (from 13.1 x86_64 "Bottle" at Telcontar)