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Step 4Capacitors, Motors, and Solar Cells
The capacitor used in the toy SUV is like the one shown on the left in the illustration below. It is a full 1 Farad rated for use at up to 5V. For lighter duty applications or shorter motor runs, smaller capacitors give shorter cycle times and, of course, shorter runs. The voltage listed on a capacitor is the maximum voltage to which it should be charged; exceeding that rating shortens the life of the capacitor. Many of the super capacitors intended specifically for memory backup have a higher internal resistance and so do not release their energy rapidly enough to drive a motor.
A solar engine such as the Easter engine is fine for driving motors that have an internal static resistance of about 10 Ohms or more. The most common variety of toy motors have much lower internal resistance (2 Ohms is typical) and so will drain all the energy from the storage capacitor before the motor can really get going. The motors shown in the second photo below all work fine. They can often be found as surplus or new from electronic suppliers. Suitable motors can also be found in junked tape recorders or VCRs. They can usually be singled out as having a diameter larger than its length.
Choose a solar cell or cells that will provide a voltage somewhat higher than the turn-on point of your engine under the light levels that your application will see. The real beauty of the solar engine is that it can collect low grade apparently useless energy and then release it in useful doses. They are most impressive when, from just sitting on a desk or coffee table or even on the floor, they suddenly pop to life. If you want your engine to work indoors, or on cloudy days, or in the shade as well as in the open, use cells designed for indoor use. These cells are usually of the amorphous thin film on glass variety. They give a healthy voltage under low light, and the current corresponds to the illumination level and their size. Solar calculators use this kind of cell, and you can take them from old (or new!) calculators, but they are quite small these days and so their current output is low. The voltage of calculator cells ranges from 1.5 up to 2.5 volts in low light, and about a half a volt more in the sun. You'll want a number of them connected in series-parallel. Wire Glue is excellent for attaching fine wire leads to these glass cells. Some solar rechargeable keychain flashlights have a large cell that works well indoors with solar engines. At the present time, Images SI Inc. carries new indoor cells of a size suitable for directly driving a solar engine from a single cell. Their "outdoor" solar cell of the same type works quite well indoors as well.
More commonly available from many sources is the crystalline or polycrystalline type of solar cell. These types put out a lot of current in sunshine, but are specifically intended for life in the sun. Some do modestly well in lower light, but most are pretty dismal in a room lit by flourescents.
A solar engine such as the Easter engine is fine for driving motors that have an internal static resistance of about 10 Ohms or more. The most common variety of toy motors have much lower internal resistance (2 Ohms is typical) and so will drain all the energy from the storage capacitor before the motor can really get going. The motors shown in the second photo below all work fine. They can often be found as surplus or new from electronic suppliers. Suitable motors can also be found in junked tape recorders or VCRs. They can usually be singled out as having a diameter larger than its length.
Choose a solar cell or cells that will provide a voltage somewhat higher than the turn-on point of your engine under the light levels that your application will see. The real beauty of the solar engine is that it can collect low grade apparently useless energy and then release it in useful doses. They are most impressive when, from just sitting on a desk or coffee table or even on the floor, they suddenly pop to life. If you want your engine to work indoors, or on cloudy days, or in the shade as well as in the open, use cells designed for indoor use. These cells are usually of the amorphous thin film on glass variety. They give a healthy voltage under low light, and the current corresponds to the illumination level and their size. Solar calculators use this kind of cell, and you can take them from old (or new!) calculators, but they are quite small these days and so their current output is low. The voltage of calculator cells ranges from 1.5 up to 2.5 volts in low light, and about a half a volt more in the sun. You'll want a number of them connected in series-parallel. Wire Glue is excellent for attaching fine wire leads to these glass cells. Some solar rechargeable keychain flashlights have a large cell that works well indoors with solar engines. At the present time, Images SI Inc. carries new indoor cells of a size suitable for directly driving a solar engine from a single cell. Their "outdoor" solar cell of the same type works quite well indoors as well.
More commonly available from many sources is the crystalline or polycrystalline type of solar cell. These types put out a lot of current in sunshine, but are specifically intended for life in the sun. Some do modestly well in lower light, but most are pretty dismal in a room lit by flourescents.
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