Figure 2-11: The charge controller, multimeter, and battery are connected.
In Figure 2-11, 0.84A of current is flowing into the battery. If your current reading is negative, then current is flowing out of the battery. This means something is wrong, so check over your wiring. You should also see the current drop considerably if you cover part of the solar panel or if the sun goes away.
If the battery doesn’t need charging, then the meter should read zero, which doesn’t tell you much. You’ll have to wait until Chapter 3, when we attach some lighting to the battery, to see the charging process in action.
USING THE SOLAR CHARGER
To ensure a continuous supply of electricity, it’s a good idea to duplicate this entire design so that if one solar panel or set of wiring should fail, you have a spare. Since swapping batteries just means unclipping the alligator clips, you can even keep a stack of batteries in rotation and set a few fully charged batteries aside for emergencies. Stockpile batteries for your own base, or start a new career as a postapocalyptic battery shop owner. Money might be useless, but I’m sure you could barter electricity for food, supplies, or assistance with your next scavenging trip.
On a sunny day, if lots of current is flowing from the solar panels, you may find that the alligator clips get hot. Wrapping some tape around them will reduce the chance that you’ll burn your fingers when you swap in a new battery.
PROJECT 2: BICYCLE GENERATOR
In this project, you’ll generate power with an adapted bicycle, which doubles as a great way to stay in shape so you can outrun the undead. The design uses a car alternator to charge the car battery. The alternator is just doing what it would naturally in a car, but without an engine. The alternator includes all that is needed to charge the car battery, so in this project, there is no need for the charge controller that you used in the solar project.
NOTE
You could also adapt this project to use other forms of rotary movement. For example, you could connect it to a wind turbine, a water wheel, or zombies on a treadmill (Figure 2-12).
Figure 2-12: Zombie power
WHAT YOU WILL NEED
To make this project, you will need the following items.
ITEM
NOTES
SOURCE
Large wheels
Scavenge
Almost any will work
eBay, Scavenge
12V
Auto parts store, Scavenge
V belt, size A100
Auto parts store, eBay, hardware store, scavenge
7A or more
Auto parts store
To suit your alternator terminals
Auto parts store
To suit your alternator terminals
Auto parts store
7A
Scavenge
Simple multimeter
Auto parts store, eBay, Fry’s
12V 5W lamp
Auto parts store
10A fuse and holder
Auto parts store
Hardware store
5 feet (1.5 m)
Hardware store
This is another project that uses a multimeter as a fixture, and I would again suggest you use the cheapest possible multimeter. You will probably also find it useful to have a spare multimeter to use for testing.
CONSTRUCTION
The trick to building this project is to keep the cycle’s back wheel away from the ground. There are two ways to do this. One is to make (or scavenge) a stand designed to allow a regular bike to be used as an exercise bike. This needs to be strong enough to support you when you sit on the bike, so a maintenance stand probably won’t be strong enough.
The other approach is to turn the bike upside down. Then you can use the pedals with either your hands or your feet while you sit in a chair near where the handlebars used to be. I used the upside-down bike approach.
ALTERNATORS
If you know a little about electronics, you may be aware that most DC motors can be used to generate current. Moving a coil of wire in a magnetic field (usually supplied by a regular magnet) will cause a current to be generated in that wire.
Alternators, like all generators, operate on this basic principle, but instead of a normal magnet, the magnetic field that the generating coil turns in is created by an electromagnet. The electromagnet is powered by the alternator itself once it gets going. To get going, the alternator must be connected to the battery; other-wise, there will no magnetic field for the generation to start. It’s a chicken-and-egg situation: the alternator needs to be generating current in order to generate current.
Figure 2-13 shows a simplified schematic of a car alternator.
Figure 2-13: The schematic diagram for an automotive alternator
In actual fact, the alternator will normally have three stator coils producing three-phase AC to be turned into DC (unlike ordinary domestic two-phase AC). If you want to find chapter and verse on alternators, then take a look at the description at http://www.allaboutcircuits.com/vol_6/chpt_4/8.html.
STEP 1: MODIFY THE BICYCLE
First, strip off every piece of the bike that you don’t need. You can take away the front wheel, both mudguards, and the brakes. The gears can stay.
Remove the rear wheel and remove its tire and inner tube. Then place the drive belt over the wheel and fix the wheel back onto the bike.
STEP 2: FIX THE ALTERNATOR AND BIKE TO THE 2×4
Alternators don’t have standard positions for their fixing lugs, so you may have to improvise a little here. The drive wheel of the alternator needs to line up with the cycle’s wheel, but the alignment doesn’t need to be exact, especially if you use a long belt like the one in my final arrangement (Figure 2-14).
Figure 2-14: The mechanical arrangement of bike and alternator
Use a G-clamp to fix the bike to the 2×4 using the saddle. Adjust the saddle first so that it is flat. Alternatively, you could also remove the saddle completely and make a hole of the same diameter as the saddle stem partway through the 2×4.
Where you place the alternator on the 2×4 depends on the geometry of the alternator, the bike, and the drive belt, so I can’t give you exact measurements. Fix the alternator in place once the bike is attached to the 2×4 and the drive belt is around the cycle wheel. The alternator I used had a convenient hole that allowed it to be fixed to the side of the 2×4 (Figure 2-15). The drive belt doesn’t need to be under a lot of tension, but you can create a simple tensioner with a spring or elastic strap; you can even cut the latter from the discarded bike inner tube.