# Piezoelectric phone charger ..#2

#### Tanmay SA

Joined Oct 15, 2021
1
hello,
I plan to make a Piezoelectric mobile phone charger that will convert the mechanical energy into electrical energy while walking and store it in 3.7v lipo battery. I managed to get around 1.5 to 4v from the Piezoelectric plates. I want to store this energy into the lipo battery. but the problem is that I need a charging circuit that would protect my lipo battery from over charging and causing any damage.
I don't know much about the charging circuits. so can you please tell me do I need this circuit or it would work if I maintain voltage below 3.7v only. If it is required that please recommend me some good charging circuit.

#### Yaakov

Joined Jan 27, 2019
3,755
Welcome to AAC.

The voltage you are getting from the piezo doesn’t really matter. How much current can it produce?

I suspect you will not have to worry about overcharging, charging will be your problem.

#### MisterBill2

Joined Jan 23, 2018
9,846
Yaakov is correct. It is not just the voltage, it is the power, and with a single piezo device there will not be enough power. It is an interesting concept but the numbers do not work.

#### Audioguru again

Joined Oct 21, 2019
3,853
A piezo in a shoe can generate a 1.5V pulse into the 10 million ohms input of a multimeter. Then the current is 1.5V/10M= 0.15uA for very short durations. The current is extremely low and is close to zero.

#### MisterBill2

Joined Jan 23, 2018
9,846
A piezo ignitor does produce a lot more voltage and a bit more current but only for a very short time. and the mechanical energy input is a lot more. A large stack of piezo generators might be able to provide enough power, BUT it will still take a lot more mechanical input to charge a battery..

#### MisterBill2

Joined Jan 23, 2018
9,846
The big problem, as always, is that it is seldom possible to exceed 100% efficiency, which means that at best you get out the energy that you put in. Thus for any energy capture scheme the first step is to determine just how much energy you need to get out of some system that captures energy, and then translate that amount into the units of the energy that you want to capture.

The great thing about this process is that so far it is not really dependent on what the energy capture process is, which means that you do not need to disclose anything to anybody about your idea.

Once you have determined the amount of energy you need to capture and converted it into the correct units of energy that would come from your source, (step one, above), you will be able to consider the means to be used for that capture process. That will allow you to decide if the idea is worth more effort, or not. And so far no inventing is required, only a bunch of arithmetic.
For a piezo-electric phone charger the energy required is, by estimate, about 1 amp at 5 volts for one hour, equal to 5 watts for one hour, equal to 5 watt-hours.
Looking at the output of a single piezo device it becomes clear that the phone charger would need a large set of them connected in series to get the 5 volts, and that the walk would need to be many hundreds of hours. So without a much more effective energy capture scheme this is not an effective concept.

#### Audioguru again

Joined Oct 21, 2019
3,853
Somebody installed thousands of piezos on a sidewalk and had thousands of people walk on them for hours. There was enough energy harvested to charge a capacitor which lighted one LED at 20mA for 1 hour.

Somebody used a computer fan as a DC generator and a strong wind turned it at a fast speed for hours. Only a small amount of power was harvested.

The little solar panel on a solar garden light generates electricity. But not much power.

#### DickCappels

Joined Aug 21, 2008
7,985
Then again I knew a guy who invented and patented a vertical wind turbine that could be placed next to a freeway and harvest significant amounts of power. Somebody gave him US \$20,000 for rights to the invention. Not bad for a mechanical engineer.

#### Audioguru again

Joined Oct 21, 2019
3,853
Standing beside a freeway I noticed that some cars are so streamlined that they make a little breeze but most trucks produce a hurricane. Wings on airplanes produce a powerful spinning vortex.
The piezo in a shoe does not make anywhere near as much power as the hammer in a lighter.