Mailinglist Archive: opensuse (1620 mails)

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Re: [opensuse] UPS : replacing battery with 12 volt Jelly Car Battery
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.html

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)

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