The Pill Box Battery Charger
The Pill Box Battery Charger came about because my very first project called the ‘Super Oscillator’ would run on two 9 volt batteries as well as a vampire wall module. However, it wasn’t practical to replace the batteries when 4 screws needed to be removed and the batteries had to be inserted under a rat’s nest of parts and wires. The solution was to make all future projects that could also run on batteries work with rechargeable Li-ion batteries.
Hence the Bob Beck unit was the easiest to modify and design around this concept. The really nice feature of the Pill Box BC is that it can be used on all types of batteries. As the battery becomes charged, the PBBC reduces the charging current. Eventually it stops completely or reduces to 1 or 2 milliamps. There is not much chance of boiling a lead acid or smoking a Li-ion battery with this type of technology.
I already knew I didn’t want to replace anymore 9 volt alkaline batteries so project design used 4 volt or 9 volt Li-ion whenever possible. It also became apparent that the 4.0 volt Li-ion batteries, used in computer notebooks, are an ideal replacement for the AAA 3 cell flashlight battery packs. Not all flash lights that use these 3 cell battery packs will accommodate the larger Li-ion batteries. But when they do, there is a tremendous savings in battery cost.
Building one of these units takes about ¾ of an hour and typical parts cost are under $10. Although the PBBC has a very realistic adjustable range from 3 to 24 volts, it is more practical to have multiple units. E.g. 4, 9, and 12 volts are the most common requirements. However, designing a unit with a selection switch is a great alternative.