I found this circuit, which supposedly limits the charging current to 2A max. This is for acid/lead batteries.
Then, I would like to NOT use a power transistor like 2N3055, but instead use a relay as, perhaps, follows (ignore the 1A relay rating in diagram):
I couldn't simulate it with LTSpice because I don't have the relay component. I do have Electronics Workbench but it won't run the simulator with Win10. In any case, I would like to know if it should work using a low power transistor plus relay. Also, perhaps the BD135 + 2N3055, ideally using a low power transistor instead the 3055, could be simplified using a Darlington like TIP122?
This is from the site that has the circuit:
How does the current limitation work? If the load current is 2 amps, there is a voltage of approximately 0.94 V at the terminals of the R7 resistor. This voltage charge the C2 capacitor through the R3 resistor. This voltage is applied between the base and the emitter of transistor Q1. (0.65V approximately) and activate Q1.
The transistor Q1 start to conduct and remove some of the base current from the Q3 transistor, which in turn removes a bit of base current from the Q4 transistor, which determines the amount of charge current.
So why use a 15A transitor? Why not one slightly greater than 2A?