posted 6 years ago
Hello Murray,
Ignoring the rectifier for a moment and pretending the turbine generates DC output:
The generator has a maximum voltage, called "open circuit voltage". It is determined by the number of windings and how fast it is spinning. At that voltage you can't get any current out of it.
The generator also has a maximum current, called "short circuit current". That is what you get if you would short the outputs and pretend the input was still spinning. In reality that would apply such a massive breaking force that it would stop almost instantly. The output voltage would be zero.
Both cases have in common that either current or voltage is zero, and so their product (power) is also zero. You want to avoid either.
What happens in reality is that the generator spins and creates a voltage V_gen. Now the battery is already charged to some other voltage V_bat. The wires running from the generator to the batteries have some resistance, so do generator and battery. I will call that overall resistance R_total. With that the resulting current can be calculated: I = U / R = (U_gen - U_bat) / R_total. As the battery voltage rises, the voltage differential drops and less current will flow, however the voltage is slightly higher. That current will act as a brake on the generator, slowing it down. As V_gen depends on the speed of the generator, it also drops and stabilizes at some point where the braking force is equal to that of the water.
Essentially it is a (stable) self-regulating system.