I've got a shiny new combine harv--- er, battery.

[Karel Jansens]

I recently bought one of those external laptop batteries, to ensure a full day's worth of juice for my tablet. It's one of these:
http://cgi.benl.ebay.be/UNIVERSAL-SLIMLINE-PORTABLE-EXTERNAL-LAPTOP-BATTERY_W0QQitemZ250103402599QQihZ015QQcategoryZ64 472QQtcZphotoQQcmdZViewItem

My question is this: These batteries pump out either 16 or 19 volts; would it be possible to downstep that voltage easily to 5 volts without dragging along yet another bulky transformer?

Ther reason? Well, you could see that coming, couldn't you: This thing could power my N800 for geological epochs on end when I'm out in the bush -- errr, bushing.

[luketoh]

Hi Karel,

I've lost touch with electronics...

http://www.uoguelph.ca/~antoon/circ/ps-lm317.html

Based on above, you could use a regulator and step the voltage down. Maybe some practicing electronics engineer can help you better...but it's an idea for you....

[Karel Jansens]

Hi Karel,

I've lost touch with electronics...

http://www.uoguelph.ca/~antoon/circ/ps-lm317.html

Based on above, you could use a regulator and step the voltage down. Maybe some practicing electronics engineer can help you better...but it's an idea for you....

Thanks! It's great to know that it's at least possible, even if I don't know what all the squiggly lines mean. :D

Time to eBay me an electronics engineer. Hopefully they come cheap...

[sdrman]

You need a regulator, not a transformer. A common 7805 regulator will drop the output to 5v. Thoughtfix has more on using a 7805. You'd connect your new battery in place of the 9v and put a 2mm pin plug in place of the usb ports.
http://tabletblog.com/2006/01/usb-power-injector-2.html
For best battery life, you may want to use a switching drop in replacement like this:
http://www.dimensionengineering.com/DE-SW050.htm