energy scavenging

Thread Starter


Joined Feb 14, 2013
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.



Joined Nov 30, 2010
The fact that a generator slows down when loaded is just that...a fact. You can not escape it. Finding the optimum load changes with wind speed. You will have to adjust things, and adjust again later.

The capacitor will only load the generator for a period of time, then it will be charged and stop inhibiting the speed.


Joined Feb 11, 2008
What is your microwindmill harvesting energy from?

Is this one of those silly devices trying to get usable energy to run a headlight from a tiny fan on a moving bicycle?

Like #12 said you can get a real good idea of the amount of power in W your generator makes by loading it with a few different value resistors and doing some calcs.

Whenever people talk about "energy harvesting" it makes me suspicious of the viability, like people setting up little fans that spin and "harvest energy" from the air currents made when people walk past.

If you are serious about generating any CREDIBLE amount of energy the first thing to do is load your generator with some resistors and find out exactly how much power it CAN make, and at what voltage/current the power is best delivered at. Circuitry decisions come later. :)