This circuit is capable of providing as high as 25 Amps of current at any specified voltage between 1.25 V to 30V as per the adjustment of the given pot. The current is constant irrespective of the voltage settings. The circuit can be used for charging batteries in range of 50 to 200 AH.
How the Circuit Works
The figure below shows a straightforward design of a 25 amp solar battery charger power supply circuit which would generate a constant 25 amps of current from any source which is able to generate currents in excess of 25 amps and at 32 volts maximum.
We know that the IC LM338 is specified with a maximum of 5 amp current, the IC restricts anything above this limit.
By connecting 5 of these ICs in parallel it thus becomes possible to generate a current output of about 25 amps. The great thing about using these ICs is that, these devices are internally protected from thermal runaway situations and short circuit or overload conditions.
It means the present circuit automatically becomes safe from such adverse parameters and thus becomes completely indestructible given the input is not exceeded above 32 volts.
However the ICs cannot be directly connected in parallel, because that would cause a difference in the voltages at the output from each of the ICs which in turn would cause an imbalance between the IC dissipation, this wouldn't be good for the overall functioning of the circuit.
Therefore the additional components in the form of the opamp and the transistor have been included in the circuit which controls and maintains a constant voltage output from all the ICs keeping the situation well under control.