Since you will be making your multimeter a permanent part of this project and you will also be chopping up the test leads, I urge you to use the cheapest possible multimeter. You will probably also find it useful to have another multimeter to use for testing.
In addition to the components listed above, you will need the following general construction tools:
• Drill
• Screws (assorted sizes)
• Screwdriver
You’re going to use multimeters a lot in this chapter, too. Take a look at “Using a Multimeter” on page 237 to find out more about how to use this useful little tool.
CONSTRUCTION
The most difficult part of this project is likely to be fixing the solar panel somewhere reliable, where the zombies and wind cannot displace it. A roof is probably a good idea, but it’s up to you to figure out the best place for the panel in your compound. Remember, you’re going to need to run a cable from the solar panel to the area where you plan to keep the battery and charge controller.
The diagram shows the wiring for the project (Figure 2-5).
Figure 2-5: Solar panel wiring diagram
Charge controllers are all a little different from each other, but most will have six terminals, each in pairs of + and–. One pair will connect to the solar panel, another will connect to the battery, and the third pair (not shown in Figure 2-5) will connect to whatever you want to power with the battery. For now, let’s just worry about charging the battery; I’ll show you how to use that stored energy later.
The charge controller will monitor the battery voltage and the voltage coming from the solar panel to ensure that the battery doesn’t overcharge or deplete so far that it stops accepting charge. More advanced models may have a display to show you what’s going on, but I used a very basic model, so I also used a multimeter to show how much current is flowing into the battery. If your charging controller does this for you, then you can probably do without the multimeter. In that case, the charge controller’s positive connection goes straight to the positive battery connection, without the meter in between.
STEP 1: FIX THE SOLAR PANEL
It should go without saying that the solar panel should go somewhere sunny and far out of a zombie’s reach, but near a window inside your base won’t be good enough. Ideally, it needs to be on a south-facing roof. The angle depends on your latitude. For optimal performance, the further from the equator you are, the closer to the vertical the panel should be tilted. If your base has a slanted roof, you can probably just attach the panel to the natural slope of the roof, as roofs tend to have steeper angles further from the equator to allow snow and rain to run off more easily.
You may have to improvise with wooden batons to attach the panels. The photograph shows my solar panel mounted on a roof (Figure 2-6).
Figure 2-6: Solar panel ready to make power
STEP 2: ATTACH A LEAD TO THE SOLAR PANEL
The solar panel may have screw terminals, or, as mine does, it may have a short length of wire soldered to its terminals. The lead attached to the solar panel needs to be long enough to reach inside your base, where you can ensure it stays dry. Attach a lead that can be fed through a hole on the wall or in the roof and attached to the screw terminals. Just like zombies, water is likely to find its way through any gap, so seal up holes after you have threaded the cable through. Silicone sealant works well for this.
Once the cable is inside, you can use the terminal block to extend it to the length you need, though a single length of cable without joins will be most reliable. A terminal block can be used to join the lead from the solar panel to a longer lead, which will be connected to the charge controller (Figure 2-7).
Figure 2-7: Connecting the solar panel
STEP 3: WIRE UP THE BATTERY AND CHARGE CONTROLLER
Wire up the battery, multimeter, and charge controller as shown in Figure 2-5. The red probe lead from the multimeter can fit in the screw terminal of the charge controller, but the black probe needs to connect to the battery somehow. The best way is to attach one end of the black probe to one of the heavy-duty alligator clips.
This means we need to make three leads, using the alligator clips and probe leads. For the first of these leads (labeled ➊ in Figure 2-5 and shown in Figure 2-8, I just used half of the multimeter’s black lead, with the probe cut off. However, you can use any black wire you like.
Figure 2-8: Negative battery lead
This lead will connect the battery to the negative (–) terminal of the charge controller. To make the lead, strip about half an inch (10 mm) of the insulation from each end of the wire. Connect one of those ends to the alligator clip by wrapping the wire clockwise around the loosened bolt on the clip. Then tighten the bolt so the clip grips the bare wire.
NOTE
The wire should be wrapped clockwise around the bolt so that when you turn the bolt, it pulls the wire around with it rather than pushes it away. The connection just works better that way.
Use a pair of pliers to wrap the supporting tabs at the end of the clip around the wire. These will prevent the wire from pulling off the clip if the wire is accidentally pulled on.
The second of the three leads (labeled ➋ in Figure 2-5 and shown in Figure 2-9) will go from the positive high-current terminal of the multimeter to the positive battery output of the charge controller. This lead is just the positive meter lead with the probe cut off and the insulation stripped off the last half inch (10 mm).
Figure 2-9: Positive charging lead
You’ll connect the final of the three leads (labeled ➌ in Figure 2-5 and shown in Figure 2-10) from the negative (COM) connection of the multimeter to the alligator clip that will be connected to the positive terminal of the battery.
Figure 2-10: Positive battery lead
Strip about half an inch (10 mm) of insulation from the remainder of the black probe lead of the multimeter and attach it to the alligator clip in the same way you did for the lead ➋. This new lead is going to be connected to the positive terminal of the battery.
This lead is black, however, and since the convention is that black means negative, the color could be confusing. To make the purpose of this lead more intuitive, wrap some red electrical tape around it to make red stripes and add some red tape to the “finger end” of the alligator clip.
Now use the three leads to connect everything together, ready for use (Figure 2-11). Note that most multimeters have a special positive socket just for high currents. This may be labeled 10A or 5A. Plug the red lead into that socket. Be sure to set meter to the correct range, which is DC current at the meter’s maximum available current reading.
STEP 4: TESTING
To test the solar panel, use the highest DC amps setting of the multimeter to monitor how much current flows into the battery from the panel via the charge controller. If the battery needs charging, the charge controller should attempt to charge the battery as much as possible until it is full, and the meter should show a positive reading. After the battery is full, most charge controllers will switch to a trickle-charge mode that just keeps the battery topped up.