The presented twin or split battery charger circuit with auto-changeover illustrates a method through which two 12V lead acid batteries can be charged and discharged in tandem by switching them appropriately across the charging voltages and load alternately.
This ensures that the load receives a continuous supply of power irrespective of the actual source conditions such as a solar panel, wind generator etc. The idea was requested by Mr. Mohammad Zain.
The Circuit Request
I am looking for a automatic 12 volt lead acid battery charging circuit, Which indicates when the battery is full and when it is out of charge.
Or if you can help me design a charging circuit that will use two batteries that is it will charge one battery at a time so when it gets full it will switch to the other battery
Your help will be really appreciated .
The Circuit Design
The discussed twin/split 12V battery charger circuit can be studied through the following detailed explanation:
Referring to the circuit diagram, two identical opamp stages A1/A2 can be seen incorporating the IC LM358. Both the opamps are rigged as voltage comparators.
A1/A2 are basically configured to detect the over voltage and low voltage thresholds of the respective batteries and to switch the corresponding relays for initiating the required cut-offs when the relevant conditions are detected. This is sensed with reference to their inverting input voltage levels fixed at the corresponding zener voltages.
The over charge cut-off threshold is set by appropriately adjusting the 10k preset associated with the non-inverting inputs of the battery.
The feedback resistor across the outputs and non-inverting inputs of the opamps determine the hysteresis levels which in turn decide the low battery restoration so that the relevant batteries begin charging once the corresponding lower thresholds are crossed.
Suppose battery#2 is initially fully charged, and battery#1 is being charged through the N/C of the A1 relay stage.
The connected load at this situation receives the voltage through the N/O of A2 relay since it's already in a disconnected state due to full charge condition of battery#2.
Now let's assume after a period of time battery#1 gets fully charged, A1 output goes high triggering the connected relay driver stage which disconnects the charging voltage to battery#1 by shifting from N/C to the N/O contact.
At this instant both the batteries get connected with the load reinforcing the supply to the load.
However, sooner or later battery#2 reaches its lower discharge threshold, forcing A2 to restore the charging process by flipping its relay from N/O back to N/C.
Battery#2 now gets into the charging phase leaving battery#1 to handle the load, the operations keeps repeating as long as the system stays switched ON.
For ensuring a balanced switching responses from the two stages one battery must be completely discharged while the other fully charged at the beginning when the proposed split battery charger circuit is first initiated.
The above explained twin or split 12V battery charger circuit with auto-changeover was built and tested successfully by Mr. Dipto a dedicated member of this blog.
The implementation details may be witnessed in the following images of the prototype, sent by Mr. Dipto.