This project will improve the output of your solar panel by about 40%. It uses a motor and gearbox from a 3.6v power screwdriver, however a number of different voltage motors can be used. The project has its own 6v power-supply made from five 1.2v NiCad cells and a charging circuit using a separate 3v to 6v solar panel to make the project self-sufficient and universal.
It has one advantage over many of the other designs. It can be connected to an existing solar panel that is hinged or has a pivot-point so it can move to align with the sun. You do not have to add any gear-wheel to the panel as it can be adapted to move the panel via a linkage. This is much easier to do than adding gears etc.
Here is just a few of the Power Screwdrivers available on the market. Remember, you do not need an expensive unit. The cheapest will be quite suitable, providing it is 3.6v or 4.8v or 6v.
The 3.6v power screwdriver is available from a number of electronics shops, hardware suppliers and warehouses for between $10.00 and $20.00. You do not need a charger but you will need two more NiCad cells (from an electronics store at a cost of about $2.50 each).
Here is the cost of some of the other components: The threaded rod costs about $5.00 plus $4.00 for wing nuts. You will need Solar Tracker-1 kit $15.00 plus some wood to hold the motor and gearbox and about $15.00 for 6 solar cells to produce a 3v (100mA) solar panel. Alternatively you can get a 2v solar panel and 1 NiCad cell from a Solar Garden Light for $5.00. You will need two of these. The solar panels will need to be placed in series and connected to the booster-circuit on the Solar Tracker-1 PC board, to produce the voltage required to charge the NiCads.
You will need eight solar cells (100mA type) to produce a 4v solar panel or six solar cells (200mA type) to produce a 3v solar panel to maintain the charge in the NiCads
We have included a boost-converter circuit to take the voltage from a 3v to 6v solar panel, so it will charge five NiCad cells. Normally a 6v solar panel will not do this as you need a small “headroom voltage” to delver a current to the cells. This means you need a solar panel with an output of at least 8v to charge the cells and this voltage is generally only available when the panel is receiving very bright sunlight. Our design will allow a panel with an an output as low as 3v to charge the 6v set of NiCad cells. We need a charging current of only about 30mA to replace the energy taken from the cells during normal operation so almost any small solar panel can be used. But if you are using a 6v motor, the requirements will increase to abut 100mA
We have suggested using NiCad cells because they are cheap and you will possibly have some lying around your workshop. We do not need high-capacity cells as they are constantly being charged and we only need them to convert a low-current device (the solar panel) into a high-current supply.
The motor from a 3.6v electric screwdriver is ideal, as it is cheap, comes with an inline planetary gearbox and 3 NiCad cells. You only have to find two more cells and this part of the project is ready.
If you want to use a 6v (or higher) motor, a few components will need to be changed. The supply will need to be 8v (or higher) and a 78L05 voltage regulator will be needed to supply 5v for the micro. The two LEDs will need to be replaced with 4 LEDs (or more) as shown in the modified circuit. The LEDs operate as a zener diode when the supply voltage is higher than 5v as the output of the chip is clamped at 5v via the components in the chip and the voltage on the base of the BC557 must not be lower than 0.6v (with reference to the supply rail), otherwise the transistor will not turn off. The LED also shows when one of the arms of the H-bridge is operating and this arm will also turn on the diagonally opposite arm.
THE PLANETARY DRIVE
The output from the planetary drive is approx 100 to 200RPM and although it has considerable torque, it cannot be used to directly control a solar panel. The RPM is too high and if connected to the panel, the panel can easily turn the motor “in reverse” if there is a wind. This may not be a problem, but it doesn’t provide an ideal set-up.
Further reduction is required. The best idea is to fit a threaded rod to the hex output of the power-screwdriver and place two nuts on the rod at a short distance apart so the rotary motion can be turned into linear travel. This travel can turn the solar panel 90 degrees or more to pick up the peak output of the sun, via an arm called a linkage or by a pin or finger on the actuator.
These two nuts will run up and down the rod when the rod is turned and they are held in place so the linear motion provides movement without jamming – if you use a single nut, it will try to bend-over on the rod when a load is applied – and this will stop the motor.
A simple bearing will hold the end of the threaded rod and the slide containing the nuts will provide “purchase” to prevent the rod bending and transfer the linear motion to an arm or bracket to move the solar panel.
This arrangement will prevent any wind pressure from the panel causing the motor to drive in reverse via the gearbox.
Alternatively you can use a Meccano worm drive but you will have to mount the worm and gear wheel using shafts and these components will cost more than $20.00 from a supplier. They are also much weaker than our suggestion.
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