The lithium battery can be charged with high current, but the maximum charging voltage of a single lithium battery cannot exceed 4.2V. If it exceeds 4.5V, it may cause permanent damage. The discharge voltage of the lithium battery must not be lower than 2.2V, otherwise it may cause permanent damage.

　　homemade lithium battery 3.7v to 9v circuit diagram (1)

　　A 3.6V lithium battery with very low standby power consumption is converted into a 9V boost circuit

　　homemade lithium battery 3.7v to 9v circuit diagram (2)

　　As shown in the principle circuit diagram of the charging device, the maximum output current is 20A, and the maximum charging voltage is 80V. It can be adjusted from 0V, so it can charge various specifications of batteries, and can also charge the same specifications of battery packs or series battery packs. For charging, for example, up to 5 12V batteries connected in series can be charged at the same time. Charging the battery in series can shorten the connection length, reduce the line loss, and facilitate the connection, so the work efficiency can be greatly improved.

　　It can be seen from the figure that the transformer T provides the working voltage for the double base tube V1. The double base tube V1 and the corresponding peripheral components form an oscillator, and the oscillation frequency can be controlled by RP1 and RP2. In this circuit, the values of RP1 and RP2 are quite different, so in actual work, RP2 can play the role of coarse adjustment, and RP1 can play the role of fine adjustment. This is particularly important when charging a single battery to avoid damage to the battery. The oscillation pulse generated by V1 is isolated by VD3 and triggers the thyristor VS. The size of the charging current and the voltage level depend on the output pulse of the oscillator, which is determined by the oscillation frequency. R5 is a sampling resistor, and its size depends on the ammeter. If a sampling resistor is provided in the ammeter, R5 can be omitted. R6 and C2 are damping elements used to protect the meter head.

　　The actual selected component parameters are shown in the figure. If the output voltage of any type of transformer with a power of 5W and an output voltage of about 24V is less than 0～80V and the maximum current is less than 20A, the transformer T can be replaced with another one. The base tube can also be replaced with a thyristor with higher trigger sensitivity. Special attention should be paid to: the phase line and the neutral line should be connected as shown in the figure; in actual operation, the battery must be connected before the power can be connected; after the charging is completed, the power should be cut off before removing the battery connection. The disadvantage of this machine is that it has great interference to the power grid. If possible, a high-power filter can be made to reduce the interference to the power grid.

　　homemade lithium battery 3.7v to 9v circuit diagram (3)

　　The picture shows the fast automatic charger circuit of lithium battery. Lithium batteries can be charged with high current, but the maximum charging voltage of a single-cell lithium battery cannot exceed 4.2V. If it exceeds 4.5V, it may cause permanent damage. The discharge voltage of the lithium battery must not be lower than 2.2V, otherwise it may cause permanent damage. This circuit uses the LM3420-8.4 dedicated lithium battery charging controller. When the battery voltage is lower than 8.4V, there is no output current at the LM3420 output pin (OUT), and the transistor Q2 is cut off. Therefore, the adjustable voltage regulator LM317 outputs a constant current, and its current value depends on the value of RL.

　　The rated current of LM317 is 1.5A. If you need a larger charging current, you can choose LM338 or LM350. During the charging process, the battery voltage will continue to rise. The battery voltage is detected by the input pin ④ (IN) of the LM3420. When the battery voltage rises to 8.4V (two lithium batteries), the output pin ① of the LM3420 has an output voltage, so that Q2 controls the LM317 to switch to the constant voltage charging process. The battery voltage It stabilized at 8.4V, after which the charging current began to decrease. After the lithium battery was fully charged, the charging current dropped to trickle charge.

　　When the input voltage is interrupted, the transistor Q1 is turned off and the battery pack is disconnected from the LM3420. The function of the diode D1 can prevent the battery from discharging through the LM317.