Energy Harvesting

[EnergyScavenger]

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.

 

[davenn]

Hi there
welcome to the forums

.... The voltage generated is about 4V.

is that the AC Volts from the generator or the DC Volts after the rectifier ?

following from that ....
if out of the generator, is that before or after the rectifier but no other load is connected ?
ie. SW1 open

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.

putting a load on the supply WILL cause the voltage to drop as current flows
that load will cause the generator to slow down cuz its now working harder

I assume you are using the two diodes D1 and D2 for dropping the voltage to the battery ?
they are probably not needed ... as previously explained the voltage will drop anyway when the load ( the batteries to be charged) are connected


confirm the AC voltage out of the generator, nothing else connected to it ACV = xxx
confirm the AC voltage out of the generator, with only the rectifier connected to it ACV = xxx
confirm the DC voltage out of the rectifier with sw1 open DCV = xxx
confirm the DC voltage out of the rectifier with sw1 open and a 100 Ohm resistor directly across the output of the rectifier DCV = xxx
confirm the DC voltage out of the rectifier with sw1 and sw2 closed so that the battery is connected ( no 100 Ohm resistor added) DCV = xxx

Dave

 

[Externet]

...When battery is connected, it creates a braking effect on the generator and charging ceases...

It is the opposite; charging does not cease; charging starts ! And because the amount of generation/wind is too small for the battery demand, stalls.

Do not expect a generator under load be as easy to spin as one without load. Make sure the cell to be charged is not shorted or fully discharged.