We have a small Christmas tree in our hallway. This has two strings of fairy lights, which used to be powered
by AA cells in small boxes perched up in the branches. These ran down in a couple of days, so somebody had to
find the boxes, unscrew the lid, take out the old AA cells and put fresh in. All while balancing on a chair and trying
not to disturb the decorations.
Time for some serious thinking over mince pies and coffee. We needed bigger batteries and we needed them to be
accessible when they ran down and needed replacing. So, time to fit longer leads, while retaining the correct value
of ballast resistor for each string, and time to make a battery box with bigger batteries. C size cells are readily available,
and should be capable of driving both strings for an extended period of time.
This is the final design, three C cells mounted in a sandwich box, which was just the right size for the job, besides being
four for a pound at Poundland. On/off switch and indicator led from my spare parts box. Lights plug in via low-voltage
power sockets at the rear. The alkaline cells come in at two for a pound at Poundland, so three quid for two sets. So far
it looks like each set will last a week, I switch them on around 3pm and off at 7 to 8pm.