Since Alex was born we've have an electric Fisher Price cradle swing that our kids (as babies) love to sleep in. One thing that always bothered me about these swings is they were all powered by 4 D batteries and the batteries don't last long in these swings. We were throwing out a lot of batteries in an effort to get our kids to take naps.
My first thought at reducing the waste was to use rechargeables, but the only place that carries D cell rechargeable batteries is Radio Shack. It costs $100 to get 4 batteries and a charger and they get crappy reviews.
So I decided to install a plug on the swing so it wouldn't need batteries. In retrospect it seems silly that these things don't come with plugs. Anyway, I got a refresher on volts, amps, energy and power from my dad and determined that I needed a 6 volt power supply. This was based on the fact that the swing is traditionally powered by 4 D batteries (1.5 volts each) in series.
I also estimated that the power supply needed to produce at least 500m-amps. I couldn't find anything on the amperage you get out of D cell batteries so I choose a minimum of 500 m-amps because I had a 6v DC power supply that was rated for 600mamps. The theory was that if the draw from the swing was greater that the power supply could handle, it (the power supply) would get hot and then I'd know to get a bigger power supply.
Power supply in hand I needed something to plug it into. I found and old external hard drive chassis that died a long time ago. I removed the power connector from the circuit board and soldered 2 wires to it. I actually used the volt meter in the image below to test that it was all working. Mad skills I tell ya!
Now that I had a way to connect the power supply to the swing I taped up two old D batteries (so they couldn't conduct electricity) and used them to hold the wires in place on the swings + and - terminals. This was the big test and it worked!
Nearly overwhelmed with my success so far, I moved on to making safe and good looking. I carved a hole in the back of the swing chassis near the battery pack and mounted the power connector flush with the swing chassis using crazy glue. I consider it a small miracle that I'm not permanently affixed to the swing.
Then I fed the wires behind the battery enclosure and soldered them in place so that you cant see them even when you take the battery cover off.
The finished product can still use batteries, but for the 99.999% of the time when its right next to a wall outlet, we avoid using batteries. Moreover we avoid creating the carbon footprint associated with producing, packaging, shipping and disposing of all those D Batteries! Now I'm all for using rechargeable batteries where appropriate (plug-in cars for example) but it seems to me that swings like this this should at least have the option of having a power supply.
The logo image was created using content from Wikimedia Commons and is license under the LGPL as it was created using LPGL content. Thanks to Everaldo Coelho and YellowIcon for Crystal Clear app klaptopdaemon and Crystal Clear app kcontrol and thanks to David Vignoni for the Nuvola gnome-logo.
Update Thursday February, 19th 2009: Todd Mayti (commented below) was kind enough to send instructions on his modification that allows for both a plug without removing the batteries. Instructions and pictures are available at Guest Post: Baby Swing Batteries/Plug Switch Modification.