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Clarification on impedance matching.

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Member level 1
Oct 22, 2011
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I have a small low rpm motor/wind generator and I am trying to charge up 9V battery. I observed that when I connect generator to battery (schottky diodes in between), the motor works harder and then to a full stop because of load effect by battery. I tried another trick, charging capacitor first and then use that capacitor to charge battery (manually by hand) and it works somewhat . Unusually thing there is that capacitor has to be of small value up to 200 uF, after that it increases the load on motor. At 1F it stops the motor fast. At low capacitance and manual switching, it works fine. Since I am getting 4 volts AC (open circuit) and 5mA (close circuit just before stopping the motor) I used voltage trippler (three diodes and three caps) to get about 10.1V enough to charge 9V battery.ofcourse with penalty of decreasing the current in process.

Any ideas why capacitors effect that way and if there is another way to bypass impedance created by high Farads capacitor. I managed to do it manually with low farad capacitors.
Any other way of charging without loading the motor. I tried some harvesting chips but still the same effect. I believe its because I do not understand impedance matching between generator and load.

Thank you.

Unless the battery is fully discharged, it should never stop the generator. Charging current will only flow, if the generator voltage is above battery voltage, so the generator should always start unloaded. Sounds like an unsuitable circuit.

One would record a loaded voltage versus current curve to design the charger cicruit.

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