Alkaline battery charger circuit diagram

 　　This circuit is specifically designed for charging alkaline batteries. In their respective charging circuits, the special connection method of the transistor causes it to continuously oscillate, on and off, in this way, the charge accumulated in the capacitor is transferred to the battery. When charging a 1.37V battery, the orange LED flashes approximately 5 times per minute. For a completely uncharged battery, the flashing will be faster, but as the battery becomes more charged the flashing will slow down until it stops. You can leave the battery in the charger and it will charge at a low current and maintain around 1.6V. In order to set the correct voltage , you need to connect a new, unused battery and adjust the capacitor until oscillation starts, then stop until no oscillation occurs and the circuit is ready to work. Please use the specified transistor, color LED, zener voltage and power rating as they will determine the final voltage across the battery.

　　This circuit is also a simple 9V charging circuit: it will charge to about 9.3V and keep charging at a low current: the green LED will be off while charging, and will stay on as the battery approaches its final voltage.

　　A 2.5V transformer can charge 4 batteries at the same time, although only 2 are shown on the diagram. In order to minimize interference between circuits, they differ except for the same transformer. To balance the load on the transformer, half of the charging elements use positive sine waves and the other half use negative sine waves. Please use a high frequency common emitter current gain transistor such as BC337-25 or better yet BC337-40. Sometimes the transistor's scattering parameters may prevent it from oscillating. Use a weak high frequency zener voltage : 7.5V instead of 6.8V or a green LED instead of the orange LED .

　　All types of alkaline batteries are rechargeable: charging time for a fully discharged AA or 9V battery will take 1 day, while a large D battery will take several days. The best way is not to completely discharge the battery or accumulator, but to charge it frequently for short periods of time, although this is not easy to do. Do not attempt to charge a completely discharged or slightly damaged battery.

　　I successfully tried charging NiMH batteries. Although the charging specifications for these batteries are different from those of alkaline batteries, the circuit seems to work well. Do not leave batteries in the charger forever as there is a risk of overcharging, especially with smaller batteries.