Does anyones device ever ran out of batteries but have some more that are of the wrong size?
This article explains how to construct a circuit that uses a single power source to charge two separate batteries.
It ensures both batteries are charged equally by using a special chip called an IC 555 along with other essential parts.
Anyone who want to make more use of their devices can find this circuit to be a useful tip.
What is a Dual Battery Charging Circuit:
A circuit made to charge two batteries together is known as a dual battery charging circuit.
This kind of circuit is often used in several kinds of applications where two different batteries need to be charged independently and safely.
Devices such as portable electronics, battery powered systems and automobile applications commonly use dual battery charging circuits.
Circuit Working:
Parts List:
| Type | Description | Quantity |
|---|---|---|
| Resistors (All resistors are 1/4 watt unless specified) | 33k | 2 |
| 8.2k | 2 | |
| 22k | 2 | |
| 15k | 2 | |
| 100k | 2 | |
| 470k | 2 | |
| 10k | 4 | |
| Presets 10k | 4 | |
| Variable Resistors Rx and Ry (to be calculated) | 1 each | |
| Semiconductors | Transistor BC547 | 2 |
| Diode 1N4007 | 2 | |
| Diode 15 Amp | 2 | |
| Zener Diode 14.4V | 2 | |
| IC 78L05 | 2 | |
| IC 555 | 2 | |
| Relay 12V | 2 | |
| SMPS charger for battery | 1 |
The function of the twin battery charger circuit is explained below:
With the IC 555 the circuit makes use of two similar stages.
The lower and upper charging thresholds for the connected batteries are controlled by each step.
The SMPS provides both IC 555 stages with a common power supply.
It uses relay connections and individual diodes to provide power to the batteries.
Between each IC 555 stage and the SMPS are diodes.
They ensure that there is no disturbance by separating the electricity between the two stages.
The charging process is managed by the relay.
Based on the charging thresholds provided by the IC 555 it functions as a switch to connect or disconnect the batteries from the power supply.
Reducing the current for both stages depends mostly on the resistors Rx and Ry.
By checking that every battery receives an accurate and suitable amount of electricity they protect against overcharging and undercharging.
Each batteries charging standards are set by the IC 555.
The battery is disconnected from the power supply by the relay when its voltage reaches the higher threshold.
On the other hand the relay restores the battery to the power source and starts the charging process again when the voltage falls to the lower threshold.
One can apply ohms law to find the right values for Rx and Ry based on the batteries ampere hour (AH) ratings.
For effective and secure charging the resistors must be adjusted to supply the required current.
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,
- The time required to charge the battery is known as the charging time and it often appears in hours (h).
- The batteries capacity is shown as battery Ah.
- The current that the charger provides to the battery measured in amps A is known as the charging current.
How the formula functions:
An indicator of a batteries overall electrical charge capacity is its capacity (Ah).
The charging current indicates how quickly the battery is being charged or how much current flows into it during a specific time period.
The standard technique for figuring out how many hours a battery will take to recharge is to divide its capacity (Ah) by the charging current (A).
For example if a 50Ah battery is charged with a charger that takes 5 Amps of electricity than the charging time would be:
The charging process for a 50Ah/5A battery takes ten hours to charge.
How to Build:
The below mentioned are the steps required for building a Simple Dual Battery Charging Circuit:
A schematic diagram should be made:
- Create a schematic drawing of the circuit for the twin battery charger.
- Assemble the diagrams components according to how they connect.
Calculate Pin Configurations:
- Identify the pin layouts of the relay, diodes, IC 555 and other parts.
- Consult their datasheets for exact information.
Connect the IC 555:
- As shown in the diagram connect the IC 555.
- Resistors Rx, Ry, diodes and other required connections should be included within each timer step.
Combine Relay and SMPS:
- Use diodes to supply power to each IC 555 stage after connecting the SMPS to the common power input.
- To control the connection between the batteries and the power source use the relay.
Include the Rx and Ry resistors:
- To control the current for every battery one should connect the Rx and Ry pins of the resistors.
- Calculate the resistor values using ohms law and the batteries ampere hour ratings.
Connect the diodes:
- To prevent the charging processes from interfering with one another be sure the two charging phases are placed at different locations for diodes D1 and D2.
Connection to the batteries:
- Connect the circuit to the batteries.
- One should confirm that the terminals for the positive and negative is fitted correctly
Check the PCBs circuit:
- It is advised that one must test the circuit before adding components to a PCB since this allows to find problems in the circuit and by correcting it without requiring to do any changes later.
Check the voltage thresholds:
- The voltage thresholds of the IC 555 timers must be modified to provide proper charge management.
- Modify the resistors value if only needed.
Safety precautions:
- One should follow the safety precautions that includes such as checking the polarity of components, ensuring sufficient insulation and avoiding short circuits.
Final Testing:
- Once the circuit is connected to the SMPS than monitor the charging process.
- Be sure both batteries are properly charged without going beyond.
Conclusion:
Based on the kind of batteries being used and the tasks that must be completed a few choices need to be made while building a basic twin battery charging circuit.
To prevent injury and ensure for the best results it is important to stick to the safety rules and regulations provided by battery manufacturers.
To further improve safety during the charging process circuit designers can include features like voltage monitoring and heat protection.