Charging a Battery with a Piezo-Sensor

Thread Starter

John A Bonilla

Joined Mar 11, 2017
66
Hello Everyone,

I am currently working on a project to use piezo-sensors to generate energy in order to charge a battery. Through research I have found that it is possible to use a capacitor to build up charge equivalent to voltage the battery being charged so that it discharges therefore recharging the battery slowly of course (extremely slowly) but surely. If I am in correct I hope you can give me an answer on how to do so. I was thinking to do this I could have a reference battery connected to a comparator along with the capacitor on the other end so that once the charge builds up to the voltage of the battery, and then that charge is released and sent through to the battery to be charged. Thank you for your time, and if there are any questions in order to develop a solution, I am happy to answer them.

- John
 

oz93666

Joined Sep 7, 2010
737
Without knowing the details of your sensors I am convinced it's not possible to harvest the amount of energy required ,

Where is the energy coming from ??? Sound waves ??

Convince me this is possible from an energy standpoint.
 

Thread Starter

John A Bonilla

Joined Mar 11, 2017
66
Without knowing the details of your sensors I am convinced it's not possible to harvest the amount of energy required ,

Where is the energy coming from ??? Sound waves ??

Convince me this is possible from an energy standpoint.
The energy comes from the piezo sensor that turns mechanical into electrical energy.
 

Thread Starter

John A Bonilla

Joined Mar 11, 2017
66
That we all understand.
What we want to know is, where is the mechanical energy coming from that would be sufficient to charge a battery? :confused:
Oh forgive me, the mechanical energy comes from a person walking on it. On average with a 47 microFarad cap, each step produces about 92.5 microJoules.
 

crutschow

Joined Mar 14, 2008
25,645
Oh forgive me, the mechanical energy comes from a person walking on it. On average with a 47 microFarad cap, each step produces about 92.5 microJoules.
Okay lets bring some perspective to this.
The average person takes about 2000 steps/mile so that give a total acquired energy (ignoring any inefficiency) of 185mJ per mile.
A typical AA NiMd battery can store 2Ah or 7200 ampere-seconds.
A Joule is 1W/s so, for a 1.2V battery voltage, this 7200 ampere-seconds is about 8600J of energy.
Thus you only have to walk about 8600/0.185 = 46,000 miles to charge this single AA battery. :eek:
 

Thread Starter

John A Bonilla

Joined Mar 11, 2017
66
Okay lets bring some perspective to this.
The average person takes about 2000 steps/mile so that give a total acquired energy (ignoring any inefficiency) of 185mJ per mile.
A typical AA NiMd battery can store 2Ah or 7200 ampere-seconds.
A Joule is 1W/s so, for a 1.2V battery voltage, this 7200 ampere-seconds is about 8600J of energy.
Thus you only have to walk about 8600/0.185 = 46,000 miles to charge this single AA battery. :eek:
I understand how absurd it may sound, but this is more of a proof of concept rather then an actual product. Now I need to understand how to build it
 

Alec_t

Joined Sep 17, 2013
11,739
how to build it
Crutschow has already proved that the concept is impractical, but if you want to experiment, here's a circuit, where 'Piezo' is a series stack of piezo elements to provide enough voltage when rectified to exceed the battery voltage :-
Harvester.PNG
Note that piezos have such high internal resistance that very little current flows; perhaps not even enough to overcome the battery leakage current. A comparator etc is entirely unnecessary.
 

oz93666

Joined Sep 7, 2010
737
I understand how absurd it may sound, but this is more of a proof of concept rather then an actual product. Now I need to understand how to build it
Well , your own figures have proved the concept doesn't work !

I've just searched shoe lights ... some shoes have leds in them that flash every time a step is taken , it seems even these run on a battery , which indicates it's not easy to extract power , since leds require minimal energy .

I would suggest you focus on the transducer , all the rest is easy ... The thing that suggests itself is the idea of a tube with a neodymium ball magnet inside (aprox. 5mm dia), a coil is wound round the tube , as the ball magnet rolls back and forth inside the tube , the coil extracts electrical energy (bridge rectifier, capacitor) ..

Second thoughts , a cylindrical magnet might be better that can slide easily in the tube , this should work better than a rotating sphere which will change orientation of magnetic field constantly reducing harvesting of energy.,,, But then again it might help ???
 

spinnaker

Joined Oct 29, 2009
7,835
I've just searched shoe lights ... some shoes have leds in them that flash every time a step is taken , it seems even these run on a battery , which indicates it's not easy to extract power , since leds require minimal energy .

Al Bundy was ahead of his time.

 

cork_ie

Joined Oct 8, 2011
428
I would not be prepared to dismiss you so easily. I don't think piezzo is the way to go, but innovation was always driven by people like yourself who started thinking about ways to do things.
First thing to do is try and determine what energy could theoretically be harvested each time a foot hits the ground and the forces involved etc. I am thinking strain gauges etc. Then you don't want to do anything that would increase the effort required to do the walking - it is tiring enough already. That way you will be able to determine what the theoretical maximum energy is likely to be . If practical you could then start looking at possibilities , and likely efficiencies. I think some kind of clamshell arrangement in the shoe driving a gearset and magnet may be the way to go but you would need to achieve micro engineering japanese style to make anything small enough and no one will pay $500-00 for a pair of shoes Keep thinking !
 
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