Charge and discharge control of accumulator in solar lamps
Regardless of the size of the solar lamp, a good performance charge and discharge control circuit is essential. In order to prolong the service life of the battery, its charging and discharging conditions must be restricted to prevent the battery from overcharging and deep discharge. In addition, because the input energy of the solar photovoltaic power generation system is extremely unstable, the control of the battery in the photovoltaic power generation system is more complicated than the control of ordinary battery charging. For the design of solar lamps, success and failure often depend on the success and failure of the charge and discharge control circuit. There is no charge-discharge control circuit with good performance. It is impossible not to have a solar lamp with good performance.
a. Anti-recharge control. The anti-reverse charging function, generally speaking, is to connect a diode in series in the solar cell circuit to prevent reverse charging. This diode should be a Schottky diode, and the voltage drop of the Schottky diode is lower than that of an ordinary diode. In addition, field effect transistors can also be used to control the anti-recharge function. Its tube voltage drop is lower than that of Schottky diodes, but the control circuit is more complicated than the previous one.
b. Anti-overcharge control. To prevent overcharging, a bleeder transistor can be connected in series or in parallel in the input circuit. The voltage discrimination circuit controls the switch of the transistor, and discharges the excess solar battery energy through the transistor to ensure that there is no excessive voltage to charge the battery. The key is to prevent the selection of overcharge voltage, the single-cell lead-acid battery is 2.2V.
c. Anti-over-discharge control. Because it will cause permanent damage to the battery due to over-discharge, in addition to Ni-Cd batteries, other batteries generally must have the function of preventing battery over-discharge. It should be noted that the solar battery system generally discharges at a small rate relative to the battery, so the discharge cut-off voltage should not be too low.
d. Temperature compensation. The battery voltage control point changes with the ambient temperature, so the solar light system should have a temperature-controlled reference voltage. For single-cell lead-acid batteries, it is -3~7mV/C, usually -1 -4mV/C.
LED use precautions
a. The characteristics of LED are close to Zener diode, the working voltage changes by 0.1V, and the working current may change by about 20mA. For safety, the use of series current limiting resistors under normal circumstances, the huge energy loss is obviously not suitable for solar LED systems, and the brightness of the LED varies with the operating voltage. It is a good way to use a booster circuit, and a simple constant current circuit can also be used. In short, the current must be automatically limited, otherwise the LED will be damaged.
b. The peak current of the general LED is 50~100mA, and the reverse voltage is about 6V. Be careful not to exceed this limit, especially when the solar battery is reversely connected or the battery is unloaded, and the peak voltage of the booster circuit is too high, it is likely to exceed this limit and damage LED.
C. LED temperature characteristics are not good, the temperature rises 5″C, the luminous flux drops 3%, please pay attention to the use in summer:
D. The working voltage is highly discrete. The working voltage of the same model and the same batch of LEDs have certain differences, so it is not suitable to be used in parallel. It must be used in parallel, and current sharing should be considered.
e. The color temperature of super bright white LED is 6400~3000K. At present, ultra-bright white LEDs with low color temperature have not yet entered the market, so solar LED systems made of ultra-bright white LEDs have poor light penetration capabilities, so attention should be paid to optical design.
f. Static electricity has a great impact on ultra-bright white LEDs. Anti-static facilities must be provided during installation, and workers must wear anti-static wrist straps. The super bright white LED that is damaged by static electricity may not be visible to the eyes at the time, but the service life will be shortened.