Piezoelectric mobile charger

Hi I have to make a piezoelectric mobile charger.

The piezocrystals will generate pulse charges which need to charge a mobile battery (like say BL-4CT).

I have thought of it this way:

Pressure on crystal >> Piezo-charge >> Schottky diode as rectifier >> DC to DC converter (buck, boost) >> Charges battery.

But is this correct? I am unclear of the thing as a whole, and whether I need the Schottky and how to connect it or what sort of DC to DC converter specifications I need. I need to charge mobile batteries of 3.7 V and the pressure on the piezo-crystal could be variable.

Please help.

Piezoelectric elements put out very small amounts of charge and
you would need a really high cycle rate to get useful current.
Static pressure does no work.

Its not static pressure. The pressure will be applied and then withdraw periodically - something like a person's running motion will apply the pressure which will charge the piezo cyrstal.

So in that case would it work? I need some circuitry to sort of store this energy and then then give it out as a steady and continuous dc voltage.

You will probably want some accumulator, like a diode & supercap
(or just a large cap) that a charge pump of some sort will turn into
a regulated charging supply.

Still, a few-Hz cycle rate is unlikely to give you more than
microamps time-averaged. So any power converter will need a
very low no-load active current draw.

Seriously, a "mobile charger" should at least provide a modern mobile phone's idle current (mA order of magnitude).
As dick_freebird said, the suggested technique is very unlikely to achieve this. Competitors like solar cells are
performing much better. For quick charge a night time, a dynamo with a gear and a handle would be superior, I think.

Thanks for all your replys guys. But I am still confused a little. FvM, the objective is to actually charge using a piezo-crystal. I have a crystal, I connected it to a digital voltmeter and it showed some 3.2 to 5 V when I applied some pressure on it (with my thumb). Now consider that this is kept in a shoe at a proper position so that such pressure generates some voltage as a person jogs/runs. Why would it not be useful to charge the mobile battery which is some 3.7 V?

Freebird, if I use a supercap, would I be able to "store" the energy in it and then later use it to charge the battery? Even that would be good. But how do I connect the supercap exactly and what more circuitry would be required? How would the entire circuit look, apart from it looking like a piezoelectric generator.

Why would it not be useful to charge the mobile battery?

Click to expand...

There's no doubt, that it can supply electric energy. If it's useful to charge a mobily battery, depends on the absolute amount of energy. I suggested a quantitative criterion for "useful" in my previous post. You can calculate if your scenario (piezo generator in a shoe) meets this or your own criterion of energetic functionality.

Regarding supercaps. Charging the converted energy to a supercap and transfering it to the mobile battery later doesn't increase the system efficiency anyhow, just causes additional losses. Supercaps come into play when you need to supply or store power levels, that can't be handled by a battery directly, e.g. in an electric car. Obviously the problem doesn't exist on a microwatt or milliwatt level.

Hi

See Linear-Tech site they have several new IC who can handle Piezo devices and provide regulated power

All the best

Bobi

Thanks guys

Jay_, I am also toying with the idea. I have procured 50 piezoelectric ceramic module and tried arranging them in parallel between copperplates but my sanwa multimeter has failed to read any output. I shall proceed further in my quest by using more sensitive digital multimeter or electrophore to measure charge. I would like to know:
1. How were you able to measure voltage?
2. Which piezoelectric module you used and how were you able to obtain it?
Thanks in advance, if you reply soon.

i want to know the exact voltage and current produced by the piezo crystal taht you have used..i need this for my final year project..

The voltage was peaking at 50v, then oscillating to 0v in triangular waveform in +ve and -ve coordinate. The current was abysmally low, perhaps a few order of μm.