Recent developments in double layer capacitor technology have enabled it to replace rechargeable batteries in specific secondary power storage applications (Reference 1). Capacitors offer significant advantages for a rechargeable battery, which comprises a virtually unlimited number of charge / discharge cycles, the viability of the short circuit phase, requires only a simple charging circuit overvoltage protection. In addition, storage capacitors can be quickly charged and do not cause toxic waste disposal problems when the product reaches the end of its working life.
This design example extends the earlier ideas by describing a powerfully driven capacitor charger. The combination of a powerful drive generator and high value capacitors provides a highly autonomous and environmentally clean power supply for emergency equipment and survival kits. This alternative "renewable" energy application covers a wide range of modern portable electrical and electronic devices, including cell phones , MP3 players, AM/FM radios, PDAs, handheld PCs , and flash units.
The power-supplied capacitor charger contains only a few components: a storage capacitor, a bridge rectifier, and a voltage-limiting Zener diode that protects the capacitor from excessive voltage (Figure 1). For practical energy storage experiments, you can use a 1F or 0.47 F capacitor with a maximum voltage rating of 5.5 V, such as NEC-Tokin America () (Figure 2). For larger storage capacity, you can use capacitors with higher capacitance, such as the 100 F 2.5 V Dynacap from Elna ().
You can take the light bulb out of a cheap, artificially powered flash and use its generator as a capacitor charger (Figure 4). In addition, various artificially powered products currently on the market offer the possibility of experimentation. For higher output, you can use a fixed bicycle-driven generator. These generators provide an average power of 20W to 100W, depending on the pedal power provided by the individual. The crank-actuated flash in Figure 4 initially illuminates a 2.5V, 0.15A tungsten bulb that consumes approximately 0.4W at full brightness. However, the measurement results show that the generator can provide more power and can charge the 1F capacitor to 5V in about 10 seconds. The following formula calculates the energy stored in the capacitor (capacitance value C): E = 1/2C × VMAX2 = 12.5J, and the following formula can calculate the average maximum power generation T at various times: TMAX = E / T =12.5/10=1.25 W.
You can use the following formula to calculate the effective energy EEFF of the capacitor during the discharge cycle, EEFF=1/2C(VMAX2-VMIN2), while the terminal voltage of the capacitor is changing from highest to lowest, where VMAX2 and VMIN2 represent respectively. The highest and lowest operating voltages applied to the powered device. You can store capacitors in series or in parallel. In both cases, ensure that the circuit contains appropriate overvoltage protection for the capacitor. To get the added voltage, you can add a DC/DC switching regulator to generate a stable output voltage.
Some important design considerations are the highest voltage and current ratings for diode bridge rectifiers and Zener diode DZ. The experimental measurements of the crank-start generator gave the following approximations of the open circuit voltage: maximum voltage 10 Vrms, peak voltage 14 V, maximum short-circuit current 200 mArms. For this application, an inexpensive bridge rectifier with a minimum peak reverse voltage of 20V and a minimum forward current of 0.5 A provides sufficient headroom. The breakdown voltage rating of the DZ should be slightly lower than the maximum operating voltage of the storage capacitor, and the rated power of the diode - 2 W in this application - should exceed the maximum output current of the generator and the conduction voltage of the Zener diode. product.
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