Greetings, homemade radio amateurs!
In recent years, bicycles have not lost their popularity as a means of transportation, and in fact, in the summer, they are a great way to get around. While most people use a bicycle only within the city, for commuting or just walking, some consider the bicycle as a means of transport for travel. Cycling has its own special passion, because the rider does not just look at the world through the window – he literally is in unity with the world. At the same time, such trips can undoubtedly be called ascetic, because a full trunk of things, like on a car, cannot be taken with you, and even electricity at such moments will seem like a luxury. You can take a portable battery of any capacity (power bank) with you, but sooner or later it will still be discharged if you actively use it to charge phones, cameras, bicycle lights. Alternatives for avid cyclists are generators, dynamos powered by the force of the rider's legs. An example of such a device in the picture below, the generator is located directly in the bushing, while it does not take up additional space, it is protected from moisture and dust.
Since the strength of the cyclist's legs is not infinite, the power of such generators is also small. Usually it does not exceed 2-5 W, because with increasing power, the resistance to pedaling will also increase. Nevertheless, even this power is enough to charge phones while driving. But it will not work just to connect the generator output to the phone input – the voltage from the generator, firstly, is variable, and secondly, it is not stabilized and at high wheel rpm it can significantly exceed 5V (the required level for the phone), which will lead to the breakdown of the phone. In order to “make friends” the generator with the phone for charging the latter, there is the following scheme.
The alternating voltage from the generator is first rectified by a diode bridge on diodes D1-D4. Please note that the diode bridge consists of Schottky diodes – they, firstly, cope better with rectifying high-frequency voltage, and secondly, they have lower losses due to a smaller voltage drop across the junction. Instead of those indicated in the diagram, 1N5819 diodes are also suitable. After that, the rectified voltage is smoothed by capacitor C1, given that voltage surges may come from the generator at some moments, this capacitor must be rated at least 25V. Capacitor C2 – ceramic, serves for better filtering of high-frequency interference. Further, according to the diagram, the LM317 microcircuit follows in a standard connection – a voltage stabilizer, the divider ratings in the strapping are designed for an output voltage of 5V. Capacitor C3 serves for additional filtering of pulsations at the output. D7 – LED, always on when voltage is supplied from the generator, serves for indication and, if necessary, can be excluded from the circuit. The output voltage is supplied to the USB connector of the “female” type, into which you can then conveniently connect the plug of the cable for charging.
In addition to charging the phone, when traveling, you may need to power other equipment designed for 12V. Since the voltage from the generator under load does not exceed 12V (for the generator used by the author), it must first be increased; for this purpose, the voltage doubler is present in the diagram below.
The doubler itself consists of 3 AK04V0 diodes – the same Schottky diodes that were used in the rectifier in the first circuit, as well as several capacitors. With the help of a doubler, the alternating voltage increases in amplitude by 2 times, while it is rectified, therefore, the circuit does not have a separate rectifier. Also on the diagram there are a pair of contacts for connecting the solar panel as an additional source of energy in sunny weather, the advantage of using the panel is that it will continue to generate electricity even when the movement stops, unlike a generator. After the doubler, the LM7812 stabilizer is installed on the circuit, or 78l12, which stabilizes the output voltage at 12V. The LED also signals the rotation of the generator, as in the first circuit.
Both circuits are assembled on printed circuit boards, drawings of which are given below the diagrams. Since the boards will be located on the bike, during the ride they can be exposed to strong vibration, and therefore the installation should be as reliable as possible. If necessary, you can assemble either one of the above schemes, or both, placing them in one case and making two outputs on it. The case, obviously, must be protected from moisture and dust, otherwise the circuits will not work for a long time. Happy build!
Greetings, homemade radio amateurs!