Stefan Vorkoetter’s Blog

As promised in my Too Many Power Adapters, Mozart post on December 21, I’ve completed the design and construction of a USB powered charger for two AA NiMH (or NiCd) cells. I’ve written a detailed construction article for those of you that would like to build one.

I recently went on a few trips and brought along several pieces of equipment: my laptop, my Palm PDA, two cameras, a GPS, and a phone. I also had to carry the specialized cables and chargers for all of them. The laptop, PDA, cameras, and phone each have their own charger. The GPS uses two AA NiMH cells which need their own charger. The combined bulk of the accessories exceeds that of the devices themselves, and I had to lug all of it around.

When I returned, I started looking into a better way. The first item I found was a retractable charge/sync cable for the PDA. Instead of using a wall-wart, this cable charges the PDA from the same USB port used to synchronize it with the computer. The cable I bought (from Boxwave) also has a second plug for charging a PDA accessory, which I plan to cut off and replace with a plug for my phone (they both use the same voltage). This one little item replaces two wall-warts and one specialty cable.

The cameras are more problematic. My Nikon has a small external battery charger connected to a wall-wart for power. My HP point-and-shoot has a huge power supply with input and output cables, and produces 3.3V at 2.5A, making it hard to substitute. I’ll worry about these later.

Finally there’s the GPS and its AA NiMH cells. I’ve been using a Sanyo NiMH wall charger which holds two or four cells, and plugs directly into the wall. But, it only works on 120VAC, so I need a transformer to use it in Europe. A quick Internet search turned up several solutions: 1300mAh AA cells that can be plugged directly into a USB port for charging, and two-cell and four-cell AA chargers that plug into a USB port.

The 1300mAh USBCells’ drawback is that they have only half the capacity of modern AA cells. The two-cell chargers are all slow chargers, taking about 37 hours to fully charge 2500mAh AA cells. The four-cell model can charge in about 6 hours, but is as big as the AC powered one I have now.

As a lifelong tinkerer, I decided to design my own USB powered AA charger which can charge a pair of 2500mAh NiMH cells in about 6 hours. Once I’ve perfected and built the design, I’ll write it up and post it on Stefan’s Electronic Projects Web Site.