I have thought of making a Smart Lead Acid Battery charger using the following schematic. I am not sure, if the circuit would work the way I am expecting it to, or not.
My expectations are:
The battery starts charging at constant current mode through UI, as the relay's NC connects input to U1.
When the closed circuit battery voltage crosses 14.1V (or little more), zener breakdown happens in ZD1 and Transistor Tip31 starts conducting. The relay turns on and now U2 starts getting input instead of U1.
Now the battery charges at constant float voltage of approx 14.2V (considering forward voltage drop at D2, the R4 is set in such a way that the output of the voltage regulating part is little higher than 14.2V, e.g. 14.5V.
I don't want to keep the charger always connected to battery. So, when fully charged, I would disconnect the charger manually. Which means, I don't want the charger to make any extra effort to start or stop charging automatically.
The voltage values might slightly vary, I know. But, will the following circuit, fulfill the expectation. Will this circuit, fulfill these expectations? I am also in real doubt, if I am going in right direction to charge an SLA battery in 2 modes - first fixed current then fixed voltage. Please let me know, if my expectation are right, in order to make a working charger.
Many thanks for your response in advance. I am a novice and I find Stackexchange the best place to ask an Expert. Please pardon my lack of knowledge, if anything assumed here is absolutely incorrect.