Introduction to the principle of constant current simple charger

The simple charger introduced in this article can automatically charge batteries below 24V, with a maximum charging current of 2.5A, and has constant current charging and automatic stop functions when fully charged.

Figure 4-9 is the electrical schematic diagram of the automatic charger. The 220V mains voltage is stepped down by transformer T to obtain the secondary voltage U2, which is rectified in the format of VD1~VD4 to output a DC pulsating voltage. From the positive pole point A, it passes through the normally closed contacts of the relay K1-2, R4, ammeter PA, VT1, and the battery GB and VT2 to the negative pole point B to charge GB. The size of RP1 is adjusted, that is, the base potential of VT1 and VT2 is adjusted, thereby adjusting the Icb of VT2, that is, the size of the charging current. Since the terminal voltage of the battery can reflect its charging status, taking a battery with a nominal voltage of 12V as an example, when the battery voltage rises to (12/2)*2.5=15V, VT3 is saturated and turned on, K1 is energized and attracted, the normally closed contact K1-2 is disconnected, the charging circuit is cut off, and the charger stops charging. By adjusting RP2, the upper limit value of the automatic stop when the battery is fully charged can be set.