scavenging

[Electribook]

Greetings,
I am running a micro-generator (microwindmill) to explore the concept of energy harvesting Please see attachment. The bridge is self made with schottky diodes for their low voltage drop. I attempted with mosfet however they were not better than schottky in my case. The voltage generated is about 4V. The problem I have is that circuit works fine when disconnected from battery (1.2V). When battery is connected, it creates a braking effect on the generator and charging ceases. If I use resistor alone then charging current will be in microamps (current when shorted is about 10mA) The switches are optoisolators to isolate capacitor and load from generator. I believe the braking effect is created by capacitor. Braking effect can be made by shorting the output of generator.
1) what is the optimum charging current that can be achieved?
2) I tried some harvesting chips from vendors but braking effect still occur.
Optoisolators are switched by timer powered externally for study purpose only.