Piezoelectric Battery Charger

[shreyrohilla]

For a project that I am conducting, I am trying to create a device that can successfully charge a 1.2v NiMH battery using 6 piezoelectric transducers. Per step of the device, the transducers produce around 50V and 40mA. I came up with this circuit,

but for some reason, the capacitor only charges up to 1.3–1.5v and is only able to charge the battery up from 0.8v to 1.07–1.10v no matter what. I am a little confused as to why it is not able to fully charge the battery, and if this is even the best way to efficiently charge this battery.

I am using 1n4007 diodes for the full bridge rectifiers and a 47uF 50v capacitor.

 

[FvM]

Bridge rectifiers are sketched with wrong polarity. Diode between capacitor and battery seems useless.

What's the piezo frequency? Most likely explanation is that the actual piezo current is only in a uA range.

 

[KlausST]

Hi,

Something is wrong with your diode orientations.
The bridge rectifiers generate "+" down and "-" top.
But the most right diode is reverse and the battery is reverse.
Please correct this.

(According schematic rules you should draw "+" top and "-" bottom)

******
How do you come to 50V and 40mA? Did you measre it? How?
What's the frequency?

Klaus

 

[Calm down]

The diode between the two capacitors seems to be reversed, and what I'm confused about is its role there? I agree with FVM's second point that your current or voltage source energy is insufficient.

 

[dick_freebird]

Piezo V,I may be what you say but pulse width may be so narrow that significant "backwash" steals from every pulse. The 1N4007 capacitance and reverse recovery charge may eat most of it.

If you have measured piezo output before, measure it again in situ. Then explain to yourself the difference, leading to "what next?".

 

[albbg]

I think it depends from both the width of the pulses generated by the sensor as well as its output impedance

 

[FvM]

Piezo energy harvesting mostly uses resonant transducers, respectively expect symmetrical waveforms. If energy source is some kind of mechanical vibration, frequency won't be high, most likely < 1 kHz.