There are some old lithium batteries in your hands. There is an elimination of your phone. There is also removed from the laptop battery pack. It has been used, and the capacity has dropped. I don't know how much capacity, I plan to be a simple circuit to measure. After repeated trial. A measurement circuit that meets the requirements is designed, which does not need to be powered up, and the circuit is powered by the lithium battery itself. It is more convenient to use. Because only need to know the substantially capacity, it is not necessary to draw the discharge curve, so the small stone watch is used. Cheap and easy. The shell is modified using a scrapped mobile phone battery universal charger, and uses the original parts in it as much as possible. It is easier to make.
Figure 1 is the simplest battery capacity measuring circuit. A lithium battery suitable for the discharge protector, a constant current circuit consisting of Q1, Q2, R1, R2, and the battery is discharged, D1, D2 to obtain a 1.5V voltage. Power supply to the small quartz table for time. The disadvantage of this circuit is that the accuracy is not high, the actual current is far less than 100mA, and the small quartz table is still timing. The measured capacity is large.
Figure 2 is based on Figure 1, increasing a voltage detecting circuit based on TL431. After the battery is discharged to the set voltage, the discharge current is cut off, and it is more suitable for a battery that is not discharged. It also prevents small current from discharged to obtain accurate capacity values. When SW2 is disconnected. Two 3.3Ω resistors are connected in series. The discharge current is approximately 100mA, and the length of the quartz table is multiplied by the battery capacity (MAH), the closing switch SW2, the discharge current doubles, that is, 200mA, can save half test time for larger capacity battery measurements. If only the small-capacity lithium battery is measured, SW2 can be not installed.
The work or not of the constant current circuit is determined by the partial pressure of IC1 and R7 and R8. The cut-off operating voltage of this circuit is 3.3V, of course, it can also be changed to other voltages (such as cut off 3V), just adjust R7, R8. The cutoff voltage is set to 3.3V because the lithium battery voltage has dropped to 3.3V in the test, and the discharge current has dropped to less than 100mA, and the actual amount of power is not much, the cutoff voltage is too low to the battery. R6 provides a positive feedback, which can speed up the circuit, while generating a backgree of about 0.3 V, the battery voltage dropped to 3.3V, and the circuit is immediately rising to 3.5V, which can avoid frequent operations of the circuit.
LED3 and IC2 constitute a discharge indication circuit. During the discharge, the LED3 is flickering at a frequency of 2 Hz, and the IC2 has two packages in TO92 and soft packages, and its pin is arranged as shown in FIG. LED1 is battery-reverse indication, and LED2 is battery access indication. After the discharge is completed, it is still lit, reminds you to take the battery as soon as possible.
Q1 uses 8550 in the original charger, or the PNP type triode of ICM>300 mA in 9012. Q2 can be selected from 9015, A1015 and other small power PNP silicon tube, and the magnification is large, generally greater than 150. D1, D2, with common 1N4000 series rectifier diodes, two forward voltage drops are 1.5V.
R1, R2, R3 use 1/8 W metal resistance, other resistors 1/8 W or 1/16 W can be. IC1, IC2, LED and battery polarity switch SW1 use the original charger, some universal chargers may have no flashing integrated circuit, which can be replaced by a dozens of ohms on the LED3 instead of IC2. SW2 is a small horizontal dial switch.
Author: Yuan Jiqing
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