Simple Dual Battery Charging Circuit

Ever run out of batteries for your device, but have some spares that are the wrong size?

This post shows you how to build a circuit that lets you charge two different batteries using just one power source.

It uses a special chip IC 555 and other basic parts to make sure both batteries get charged equally.

This is a handy trick for anyone who wants to get more use out of their electronics.

What is a Dual Battery Charging Circuit:

A circuit for twin batteries that charges two batteries at once is called a dual battery charging circuit.

When two different batteries need to be charged effectively and separately, this kind of circuit is frequently utilized in a variety of applications.

Devices such as automobile applications, battery powered systems and portable electronic gadgets frequently use dual battery charging circuits.

Circuit Working:

Parts List:

Below mentioned is the working of the dual battery charger circuit:

The circuit utilizes two identical stages with IC 555.

Each stage is responsible for managing the charging thresholds lower and upper of the connected batteries.

The SMPS serves as the common power source for both IC 555 stages.

It supplies power to the batteries through individual diodes and relay contacts.

Diodes are placed between the SMPS and each IC 555 stage.

They ensure that the power is isolated between the two stages preventing any interference.

The relay is employed to control the charging process.

It acts as a switch to connect or disconnect the batteries from the power source based on the charging thresholds set by the IC 555.

The resistors Rx and Ry play a crucial role in reducing the current for both stages.

They ensure that each battery receives an accurate and appropriate level of current preventing overcharging or undercharging.

The IC 555 set the charging thresholds for each battery.

When the voltage of a battery reaches the upper threshold the relay disconnects the battery from the power source.

Conversely, when the voltage drops to the lower threshold the relay connects the battery to the power source, resuming the charging process.

To determine the correct values for Rx and Ry you can use ohms Law in accordance with the ampere hour AH ratings of the batteries.

The goal is to set the resistors in a way that provides the desired current for efficient and safe charging.

Formulas and Calculations:

The formula for charging time represents the time required to fully charge a single battery in a constant current charging scenario:

Charging Time = Battery Ah / Charging Current

here,

• Charging Time: Usually expressed in hours (h), this is the amount of time needed to charge the battery.
  Battery Ah: This indicates the batterys capacity.
• It shows the maximum current the battery is capable of providing for a given period of time (usually an hour).
• A 100Ah battery, for instance, has the potential to deliver 1 amp of electricity for 100 hours, 5 amps for 20 hours, and so on.
• Charging Current: This is the current, expressed in amps A, that the charger supplies to the battery.

How the formula functions:

The entire quantity of electrical charge that the battery is capable of storing is indicated by its capacity (Ah).

The pace at which the battery is being charged that is, the amount of current that is flowing into it per unit of time is indicated by the charging current.

You can calculate how long it will take to recharge a battery by dividing its capacity (Ah) by the charging current (A), which will give you the time in hours.

For instance, the charging time for a 50Ah battery using a charger that provides 5 Amps of power would be:

Charging Time = 50Ah / 5A = 10 hours

How to Build:

Below is a general guide on how to build the proposed dual battery charger circuit:

Create a Schematic Diagram:

• Sketch a schematic diagram of the dual battery charger circuit.
• Place components on the diagram according to their connections.

Identify Pin Configurations:

• Understand the pin configurations of IC 555, diodes, relay and other components.
• Refer to their datasheets for accurate information.

Connect IC 555 :

• Connect the IC 555 as per the schematic.
• Each timer stage should include resistors Rx, Ry, diodes and necessary connections.

Integrate SMPS and Relay:

• Connect the SMPS to the common power input and distribute power to each IC 555 stage through diodes.
• Use the relay to control the connection between the batteries and the power source.

Add Resistors Rx, Ry:

• Connect the resistors Rx and Ry to regulate the current for each battery.
• Calculate the resistor values using ohms Law and the batteries ampere hour ratings.

Connect Diodes:

• Place diodes D1, D2 to ensure isolation between the two charging stages.
• This prevents interference between the charging processes.

Wire the Batteries:

• Connect the batteries to the circuit.
• Ensure that the positive and negative terminals are correctly aligned.

Test the Circuit on a PCB:

• Before soldering components onto a PCB, it is advisable to test the circuit on a PCB.
• This allows you to identify and rectify any issues without permanent changes.

Check Voltage Thresholds:

• Set the voltage thresholds on the IC555 timers for proper charging control.
• Adjust resistor values if necessary.

Safety Precautions:

• Observe safety precautions such as checking the polarity of components, ensuring proper insulation and avoiding short circuits.

Final Testing:

• Connect the circuit to the SMPS and monitor the charging process.
• Ensure that both batteries charge efficiently without overcharging.

Conclusion:

These circuits are designed with specific considerations based on the type of batteries being used and the requirements of the application.

It is crucial to follow safety guidelines and specifications provided by battery manufacturers to avoid damage and ensure optimal performance.

Additionally, circuit designers may incorporate features such as thermal protection and voltage monitoring to enhance safety during the charging process.

References:

Dual Battery Charger System for Electric Vehicle