HOME Schematics Hobby Corner Dave's Circuits Electronic Resources Contact Info

  Experimenter's Corner

  Previous Issues

25 Watt-hour Battery Pack for Charging Devices through USB Port
By: Dave Johnson, July 21, 2012

My wife often forgets to plug her phone into its charger.  Later, the phone runs out of juice.  I thought it would be nice to have a compact battery pack which could conveniently fit in her purse and be switched on to charge not only her phone but any device which draws power from a USB port.

There are some new AA size lithium ion batteries available which might work for this application.  They claim to have a capacity of 2.2 Amp hours.   Four such cells held in a box would yield a 14v pack with a 2 Amp hour rating.  That is 28 watt-hours of energy which is much higher than four alkaline or NiMH
cells.  An efficient 5v 1 Amp DC to DC converter could be mounted inside another small plastic box and glued to the side of the battery box, together with a USB socket and perhaps a DC power jack.  When needed, my wife could then connect the pack to her phone, switch on the charger and charge her phone’s battery.  The power jack could be connected to a custom DC battery charger, able to charge the 4 AA cells.  At a standard 4.2v per cell voltage, the charger would need to apply 16.8v to the pack and charge the pack at a 200ma or C/10 rate.  The pack would then be fully charged over night.
With 2 Amp-hour cells and an 85% converter efficiency, the total energy available from the 4 cell pack is about 23 watt-hours.  This is roughly 4 hours of full 5 volt 1 Amp power.  That should be enough to charge a number of different devices.  It would be an interesting experiment to put together such a device and see how it works.

3.6v AA Lithium Ion Battery   4 AA pack with USB and on/off Switch   5v 1 Amp DC to DC Converter

Please send comments to me

Third Quarter, 2012    

Page 1 Circuit
Good Idea
gone Badly
What the World
needs Now
Wily Widget

Imagineering Ezine    Discover Solar Energy Dave Johnson & Associates Faraday Touch Switches

 About Us   |  Advertise on DiscoverCircuits.com   |   Report Broken Links  |    Link to DiscoverCircuits.com  |   
Privacy Policy

Discovercircuits.com endeavors to credit original designers.   Please alert us by eMail so we can
delete links to material that have been copied without your permission
.   Thank you.

© Copyright of all original material on this website is the property
of David A. Johnson, P.E. (Dave Johnson & Associates ) unless otherwise noted.  

Linking is ALLOWED but COPYING any content or graphics to your web site is EXPRESSLY PROHIBITED.
All material is provided "as is" without guarantees or warranty of any kind, either expressed or implied.