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SolarRecharger Battery Kit
Do It Yourself (DIY) Instructions
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Working with renewable energy sources is dangerous. Since you aredealing with electricity, high roof tops or towers, and numerous otherunknown conditions, seek expert opinions and help where necessary. Theauthors and publishers assume that, while carrying out your DIY project,you are aware of all the risks and possible damages associated with homeimprovements and renewable energy.
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Solar Recharger Battery Kit
Renewable energy systems create power in direct current or DC. While this
DC power must be inverted to alternating current to run most of your household
appliances and electronics it is well suited for charging batteries since batteries
store and provide DC power. Laptops, for instance, run on DC power from the
battery.
To charge the battery from your standard 120 volt wall outlet, it requires a
mini inverter to take the 120 volts AC power from the wall power source and
invert that to a lower voltage output in DC. This mini inverter is the little black
box that you see attached to the cords for all laptops.
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Many small electronics are powered in this manner. Whenever you see
that little black rectangular box your device is running on inverted DC power.
AA batteries are a good fit for charging with solar cells, since they have a
low voltage of just 1.5 volts per battery and dont take long to charge. A
rechargeable 1.5V AA battery will typically have a storage capacity of around 1600
milliamp hours (mAh). Just as you need around 16 18V to charge a 12V battery,
you also need more voltage from your solar battery charger than the battery will
provide in order to force the extra current into the battery, thereby charging it.
Using the water analogy, envision two pipes with flowing water meeting up in the
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middle. Voltage is comparable to the pressure of the water. If the water pressure
is higher in pipe A than in pipe B the water will flow from pipe A to pipe B. If pipe
Bs pressure is higher than pipe A the water will flow from pipe B to pipe A. To
charge a 12v battery, you need to supply more pressure to it (a higher voltage)
to force the current into the battery cell and charge it.
Current can be compared to the amount of water that is flowing. Think of a
battery like a water tank. If the pressure going into the tank is higher than the
pressure coming out of the tank then you will fill the tank with water. Depending
on how much water is flowing dictates how fast the tank will fill up. Likewise, it is
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dependent on how much current is flowing from the solar panel to determine
how fast the battery will fill up with power. Conversely, this is why solar panels
without a blocking diode will drain batteries at night time. Once the sun dips
below the horizon, the voltage from the solar panel will drop below the 12v being
supplied from the battery. When this happens, the pressure from the battery is
higher than that from the solar panel and the current will flow into the panel.
With this in mind, 2 volts will be enough to charge a 1.5V battery.
To obtain the desired 2 volts we will begin by wiring 4 solar cells in series.
Remember each solar cell, regardless of size has a voltage of .5V, so 4 cells wired
in series is:
.5V/cell x 4 cells = 2.0 volts
Since a standard full sized 3 x 6 solar cell will deliver around 3 amps of
current, using 4 full sized cells wired in series will provide more current than
needed and you risk overcharging the batteries. It is important to remember the
nature of solar cells with respect to voltage and current. No matter what the size
of a solar cell it will always deliver .5V, while its surface area is directly related to
the current produced. For example, a 3 amp cell cut in half will deliver 1.5 amps,
while still delivering the same .5V. For the purpose of this guide, we will be using
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4 cells wired in series that will produce approximately .3 amps under full sun. To
charge a 1.5V AA battery with storage capacity of 1600 mAh (milliamp hours), also
written as .16 Ah it will take a .3A, 2V solar panel about a half hour to fully charge
the battery.
.3A x .5 hours = .15Ah
If more batteries are being charged at once it will take longer (2 batteries
will take twice as long, 4 will take 4 times as long). If the battery, or batteries, are
at a partial charge before being connected to your solar battery charger the total
charge time will decrease. Take care not to overcharge the batteries, as under
pressure they may leak or explode.
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To carry the current from the solar panel to the battery you will need to
size the conductors to allow for the necessary current to pass through without
too much resistance in the wire, resulting in voltage drop. More than likely, this
wont be too much of an issue, as youll have low current flowing from the solar
panel and the wire to the battery holder doesnt need to be more than a couple
of feet.
Once you have connected the positive and negative conductors to the
positive and negative panel leads you need to connect the other end to a landing
strip of a conductive metal, such as aluminum.
By connecting the positive and negative leads through the wire to the metal
you are effectively energizing the metal, which will help complete the circuit once
the batteries are in place. Buy angled aluminum so that youll have somewhere
to attach the metal to the wood substrate and also attach to the terminals ends
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of the battery. Measure the length of the battery and screw the two pieces of
aluminum to the wooden substrate. Plastic would work for a substrate, too, just
make sure that your substrate isnt conductive and wont carry the current across
the positive and negative terminals otherwise you run the risk of shorting out
your circuit. Use conductive screws to attach the two aluminum pieces to the
wood otherwise youll lose a lot of your power!
Cut the aluminum pieces to make separate connections for each battery
you plan on charging. This gives each battery a secure place to charge, with a
positive and negative depression made on opposing sides to aid in the security.
This can be done in numerous ways, but I choose to drill out a pilot hole in
between each battery placement and use metal snips to cut from the edge of the
aluminum strip inwards to the pilot hole.
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This gives individual terminal holders for each battery. The number of
separate terminal ends to make depends on the length of the aluminum you are
using and the number of batteries you wish to charge.
Make little indentations in the positive and negative sides of the aluminum
to allow the batteries to hold in place and make a better connection. Make an
indentation inward for the negative side and an indentation outward for the
positive side. This is easily done with a nail and a hammer. Place the nail firmly
against the metal and tap with a hammer until the desired depression is made.
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Snugly place the rechargeable AA batteries in the holder, making sure that
the positive terminals on the battery are aligned with the positively charged metal
holder and the negative terminal to the negatively charged metal holder, place
the solar panel under the sun and you done!