How to build electricity that depends on slim dual

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How to build a battery charger that relies on slim dual cell solar panels

nowadays, the development of low-power electronic technology allows the placement of battery powered sensors and other devices away from electricity. Ideally, in order to really get rid of the shackles of electricity, the need to replace the battery should be eliminated, and the battery should be recharged by mechanical and hydraulic 1 General low-frequency renewable energy (such as solar energy) provided by the local environment. This design point explains how to build a compact battery charger that relies on small dual cell solar panels. The unique feature of this design is that the dc/dc converter uses power point control to absorb the maximum power from the solar panel

importance of maximum power point control

although solar cells or solar panels are classified according to power output, the available power of solar panels is rarely constant. Its output power largely depends on the light, temperature and the load current absorbed from the battery board. To illustrate this, figure 1 shows the V-I characteristic curve of a dual cell solar panel under constant light conditions. The I-V curve has a relatively constant current characteristic in the range of short circuit (leftmost) to about 550mA load current, and then it follows the constant voltage characteristic under low current conditions, and approaches the maximum voltage when open circuit (rightmost). The power output curve of the battery panel shows that the power output has an obvious peak at about 750mv/530ma (at the inflection point of the I-V curve). If the load current increases beyond the peak power, the power curve quickly drops to zero (leftmost). Similarly, light load will also make the power tend to zero (far right), but this is often not a problem

Figure 1: output voltage, current and power of solar panels

of course, the lighting conditions of solar panels will affect the available power - less lighting means lower power output; More light means higher power output. Although illumination directly affects the magnitude of peak power output, it has little effect on the position of peak on voltage scale. That is, the output voltage of the panel with peak power remains relatively constant regardless of the light. Therefore, it is wise to adjust the output current appropriately so that the voltage of the solar panel is at or higher than the peak power voltage (750mv here). This practice is called maximum power point control (MPPC)

Figure 2 shows the influence of the change of sunlight on the charging current with and without maximum power point control. The intensity of simulated sunlight decreased from 100% to about 20%, and then increased to 100%. Please note that when the sunlight intensity decreases to about 20%, the output voltage and current of the solar panel also decrease, but LTC? The maximum power point control of the 3105 can prevent the output voltage of the solar panel from falling below the set value of 750mv. It realizes the above functions by reducing the output charging current of ltc3105 to prevent the solar panel voltage from plummeting to close to 0V, as shown in the curve on the right in Figure 2. When power point control is not adopted, the small decrease of sunlight intensity will completely block the flow of charging current

Figure 2: changing the intensity of sunlight will affect the energy demand of plastic machinery such as plastic granulator. The charging current is very large. Ltc3105 boost converter with input power control function is a synchronous boost dc/dc converter, which is mainly designed to convert the power from environmental energy sources (such as low-voltage solar cells and thermoelectric generators) into battery charging power. The ltc3105 uses MPPC to transmit the maximum available power from the energy source. It realizes this function by reducing the output current of ltc3105 to prevent the voltage of the solar panel from plummeting to close to 0V. The ltc3105 can be started at an input voltage as low as 250Mv, thus enabling it to be powered by a single solar cell or up to 9 or 10 batteries connected in series

the output disconnection function eliminates the isolation diode often required by other solar powered dc/dc converters, and allows the output voltage to be higher or lower than the input voltage. During startup and according to the creativity discussed, the switching current limit of 400mA is reduced in order to rely on the power supply with relatively high impedance, but once the converter is in normal operation, it can still provide sufficient power suitable for many low-power solar applications. In addition, ltc3105 also has a 6mA adjustable output low dropout linear regulator, good output of open drain power supply, shutdown input and burst mode Operation capability to improve the efficiency of low-power applications

solar powered lithium-ion battery charger

Figure 3 shows a compact solar powered battery charger, which uses ltc3105 as a boost converter and ltc4071 as a lithium-ion battery parallel charger. A dual battery 400MW solar panel is responsible for providing input power for ltc3105 to generate a charging current of more than 60mA in sufficient sunlight. As shown in Figure 1, the maximum power point control can prevent the voltage of the solar panel from falling below the maximum power point of 750mv. The output voltage of the converter is set to 4.35v, which is slightly higher than the 4.2V floating voltage of the lithium-ion battery. Ltc4071 parallel charger limits the voltage at both ends of the battery to 4.2V. Grounding the fbldo pin can set the low-voltage differential regulator to 2.2V, which is used to supply power to the "charging" led. The LED turns on when the battery is charged, and turns off when the battery voltage is within 40mv of the floating voltage (to indicate that the battery is nearly fully charged). An NTC thermistor is used to sense the temperature of the battery and reduce the floating voltage of ltc4701 to improve the safety of the battery when the ambient temperature is very high. It is generally called an analyzer. To prevent the battery from being damaged by excessive discharge, the low battery disconnect function can disconnect the battery from the load when the battery voltage drops below 2.7V

Figure 3: dual cell solar panel and lithium-ion battery charger


although the circuit described in this paper can produce only a few hundred MW of power, it can provide enough power to keep a 400mahr lithium-ion battery fully charged under most weather conditions. The combination of low input voltage and input power control makes ltc3105 an ideal choice for low-power solar applications. In addition, ltc4071 parallel charging system also complements ltc3105 by providing accurate floating voltage, charging state and temperature safety characteristics, which can ensure long battery life in outdoor environment. (end)

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