Solar NiCad Battery Charger

In the realm of renewable energy, solar power stands out as one of the most accessible and abundant sources. With the ever-increasing demand for sustainable energy solutions, utilizing solar power to charge batteries has gained significant attention. This article introduces a circuit designed specifically for low-power or low-ampere-hour nickel-cadmium (NiCad) battery chargers, providing an effective and eco-friendly solution for charging small NiCad batteries using solar energy. By incorporating a voltage regulator for consistent charging voltage and utilizing up to 12 solar cells, this circuit ensures optimal performance without the risk of overcharging or damaging the batteries. Delve into the details of this circuit, its components, and its working principles to explore the potential of harnessing solar energy for small-scale battery charging needs.


This circuit is designed for low-power or low-ampere-hour nickel-cadmium battery chargers. Up to 12 solar cells are used in this project to charge the battery. The circuit includes a voltage regulator, which ensures a consistent charging voltage for the battery. With this circuit, you can effectively charge small NiCad batteries without worrying about overcharging or damaging them.

If you design a solar controller to charge high-power batteries, we recommend you check the above-mentioned articles. This circuit is designed to charge low Ampere-hour batteries.

List of components for solar NiCad battery charger

  • Resistors,”R1″,820k,
  • Resistors,”R2″,75k,
  • Resistors,”R3″,75k,
  • Resistors,”R4″,1M,
  • Capacitors,”C1 / 16 volt,47uF,
  • Capacitors,”C2 /40 volt”,100uF,
  • Integrated Circuits,”U1″,MAX639 Integrated circuit
  • Diodes,”D1″,1N57117,Zener diode
  • Diodes,”D2″,1N57117,zener diode
  • Miscellaneous,”L1″,100uH, coil type inductor

Circuit Diagram of Solar NiCad Battery Charger

This section describes a circuit diagram for solar charger for NiCad battery chargers. The circuit diagram shows that 12 solar cells are being used to charge the battery. The circuit also utilizes the MAX639 integrated circuit to regulate the charges from the solar cells to the NiCad battery.

solar NiCad battery charger
solar NiCad battery charger

MAX639 Function and Working

MAX639 is a switching regulator which is used to step down voltage. It provides a wide range of output current. It can provide maximum output current of 200mA in safe range. It has a very high-efficiency due to pulse frequency modulation function. Input voltage range to MAX639 is 4-12 volt. It can provide output voltage from 1.5 volt to maximum input voltage.

Applications MAX639

It can be used in various configurations in many projects. Some of the major applications of MAX639 are given below:

  • Battery chargers
  • Solar chargers
  • Voltage regulator
  • DC to DC converters

1N57117 Zener diode is used to provide a constant voltage to the battery.

How Does This Circuit Work?

To explain the workings of this circuit in more detail, let’s break it down into its components. The heart of the circuit is the solar panel, which converts sunlight into electrical energy. The number of solar cells used depends on the desired charging current and the capacity of the battery you want to charge. In this case, up to 12 solar cells are used, although you can adjust this number according to your requirements.

The solar panel is connected to a current-limiting resistor and a diode. The resistor limits the charging current flowing into the battery, preventing it from exceeding the recommended value. The diode ensures that the current flows only in one direction, preventing any reverse current from the battery during periods of insufficient sunlight.

The charging current of the battery should not exceed 200mA to prevent overcharging. To regulate the voltage and current, a voltage regulator is used. This regulator maintains a constant output voltage regardless of variations in the input voltage or load conditions. It provides a stable charging voltage for the battery, ensuring optimal charging performance.

It’s important to note that this circuit is specifically designed for low-power applications and smaller NiCad batteries. If you require a higher power or current solar charge controller, you may want to explore other articles and circuits that I have previously posted. These articles provide guidance on building high-power solar charge controllers suitable for larger batteries and higher charging currents.

Remember, when working with electrical circuits and batteries, exercise caution and ensure proper safety measures are in place. Additionally, as the overall performance of the circuit can vary based on different factors, such as sunlight intensity and battery condition, it’s always a good idea to monitor the charging process and make any necessary adjustments.


In conclusion, the circuit described in this article provides an effective solution for charging low-power or low-ampere-hour nickel-cadmium batteries using solar energy. With the inclusion of a voltage regulator, the circuit ensures a consistent charging voltage, preventing overcharging and potential damage to the batteries. The use of up to 12 solar cells allows for efficient power conversion from sunlight to electrical energy. However, it is important to note that this circuit is specifically designed for smaller NiCad batteries and low-power applications. For high-power batteries, it is recommended to explore other articles and circuits that specialize in such requirements. By following proper safety measures and monitoring the charging process, this circuit can serve as a reliable and sustainable solution for charging small NiCad batteries with solar energy.

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5 thoughts on “Solar NiCad Battery Charger”

  1. I’ve been looking to build your design but I am having trouble locating the Zener Diode with the number you provided and you do not define a specification or rating on the Diode. Could you please provide additional information on components?
    Thank you in advanced.
    Best regards,


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