WHAT YOU WILL NEED
To make this project, you’ll need the following items.
ITEM
NOTES
SOURCE
12V
Auto parts store, scavenge
7A or more
Auto parts store
12V 2W-10W
Hardware store
Sockets with trailing leads
Hardware store
Inline switch (5A)
Hardware store
7A
Scavenge
10A fuse and holder
Auto parts store
CONSTRUCTION
The LED lights for this project are wired in parallel (Figure 3-5). In this arrangement, each of the lights gets the full 12V from the battery, and if one of the lights fails for any reason, the other lights will keep working.
Figure 3-5: 12V lighting system
STEP 1: PREPARE THE ELECTRICAL CABLE
If you’re using a fairly small number of low-power LED light bulbs (up to five, at up to 5W each), then double-core bell wire will be just fine. Cable designed for speakers is also a good choice. In my design (Figure 3-5), I used three bulbs, so I cut three lengths of cable, stripping half an inch (15 mm) of the insulation off the ends.
The first of these leads (labeled ➊ in Figure 3-5) will go from the battery’s positive terminal to the switch and then to the first lamp. The second length will continue on to the second lamp (➋), and the final lead (➌) will go to the last lamp.
Where the wires join, there needs to be a three-way twisting of each wire of the cable with both the next length of cable and the lamp holder (Figure 3-6).
Figure 3-6: Connecting the lamp holder
For a more permanent connection, solder the twisted connection. Whether you solder them or not, wrap the connections in electrical tape. For a guide on how to make this kind of twisted-wire connection, see “Joining Wires by Twisting” on page 229.
STEP 2: WIRE UP THE FUSE AND SWITCH
Complete the wiring by attaching the fuse and alligator clip to the start of the wiring. Note that these MR16 light bulbs include a circuit to automatically switch the polarity of the LED. This means you can connect them either way around. If you use a different type of 12V LED, check whether it has separate positive and negative connections. If so, make sure that you connect the positive side to the switch lead and the negative side to the lead you’ll attach to the negative terminal on the battery.
The alligator clip attaches to the fuse lead, which is attached to the switch (Figure 3-7). Once again, these leads can be twisted together, and for a more reliable finish, you can solder the twisted joint. The in-line switch uses screw terminals to attach the wires. One side is just a metal connector that passes straight through, and the other side has spring contacts, which connect with each other when the switch is in the on position.
Figure 3-7: Connecting the fuse and alligator clip for a lighting system
STEP 3: INSTALL THE LAMPS
Now that everything is wired up, attach the alligator clips to the battery and make sure that the bulbs light when the switch is flicked. Once you know the lights turn on, just affix them to the ceiling, the wall, or wherever you want them.
USING THE LIGHTING
Murphy’s law dictates that batteries will run out of juice and shut off the lights just as the zombies attack. To anticipate and avoid this situation, it’s good to know roughly how many hours of light you’re going to get from your battery before you need to do some more pedaling or otherwise put some juice into it.
That number of hours depends on the size and quality of your battery. Looking back at Table 2-1 on page 21, you can see that a 5W LED is expected to last 120 hours. Therefore, a string of six 5W LEDs should be good for about 20 hours. If you go all out and put up a string of three 60W 12V halogen lamps, you’ll only get about 4 hours of light before needing another charge.
Whatever your lighting setup, it would be great to have advance notice that the battery is getting low—and this is the goal of the next project.
PROJECT 4: BATTERY MONITOR
I recommend keeping a good stock of car batteries charged up and ready to go at all times. That way, if zombies damage your solar panels, or you fall ill and can’t pedal your generator, you won’t be plunged into darkness and left powerless (in both senses of the word). It is therefore of paramount importance that you have an early warning system that will monitor the battery, telling you when it starts to get low so you can swap in a new one.
This project uses an Arduino, a useful little board that’s great for putting together electronic projects that require a bit of logic. In this case, the logic is simply to measure the battery voltage, display it, and sound a buzzer when it falls below a certain critical level.
The Arduino will be powered from the same car battery that it’s monitoring. The Arduino uses less than 1W to operate, so it’s okay to leave the board connected to the battery continuously.
In the battery monitor setup (Figure 3-8), alligator clips connect the battery monitor to the battery. If the battery has large alligator clips attached to it, then these smaller clips can be attached to the handles of the big clips.
Figure 3-8: Battery monitor
The left lead of the left resistor (Figure 3-8) is connected to the positive battery terminal, and the right lead of the right resistor is connected to the negative battery terminal.
WHAT YOU WILL NEED
To make this project, you’ll need the following items.
ITEM
NOTES
SOURCE
Arduino Uno R3
Adafruit, Fry’s (7224833), Sparkfun
Screwshield
Adafruit (196)
LCD 16x2 display shield
eBay, Sparkfun (DEV-11851)
Small piezo buzzer
Adafruit (1740), eBay
Mouser (293-270-RC)
Mouser (293-470-RC)
Auto parts store