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.

 

Hi there, sounds like an interesting project. Be careful with Lithium batteries, if you don't take care they can be very dangerous.

For charging/discharging a single 18650 lithium cell you can buy TP4056 protection IC's assembled from ebay, which provide alot of protection features.

If you intend to charge more than one 18650 cell as a battery pack you should include a battery management system (BMS) to balance charge the entire pack.

 

Sorry to rain on your parade, but you'll find that you can draw only a tiny current from a piezo element that generates 4V. Piezos hav a very high internal resistance. Even if you could harvest all the energy stored in the piezo it would take you a month of Sundays to charge a phone battery. You would fare better riding a bicycle equipped with a dynamo.

 

... but the problem is that I need a charging circuit that would protect my lipo battery from over charging and causing any damage...

Are you sure there is any risk of that? I suspect that the power coming from the piezo is well below what the LiPo battery can tolerate on a continuous trickle basis. I'd bet it cannot keep up with the battery's self-discharge, let alone overcharge it.

 

I decided to quickly search this to see if anyone had claimed to do this succesfully, and found the following:

https://blog.mide.com/piezoelectric-energy-harvesting-from-walking

A pupil did this for a high school project, and she concluded it wasn't practical. Her conclusion is insightful and hilarious:

"By my calculations, it was approximately 564,971.78 charging cycles, which amounted to 2,118,644,250 steps, in a best case scenario. This also means it would take 706,214.75 hours to charge the cell phone"

So ultimately it would be an interesting learning journey I suppose but very very impractical. LOL

 

I decided to quickly search this to see if anyone had claimed to do this succesfully, and found the following:

https://blog.mide.com/piezoelectric-energy-harvesting-from-walking

A pupil did this for a high school project, and she concluded it wasn't practical. Her conclusion is insightful and hilarious:

"By my calculations, it was approximately 564,971.78 charging cycles, which amounted to 2,118,644,250 steps, in a best case scenario. This also means it would take 706,214.75 hours to charge the cell phone"

So ultimately it would be an interesting learning journey I suppose but very very impractical. LOL

hey thank you for your reply. but what I want to do is to power Arduino micro from the piezoelectricity. after charging up the battery I would use a step up boost converter in order to generate 5v to power up the Arduino.

 

Are you sure there is any risk of that? I suspect that the power coming from the piezo is well below what the LiPo battery can tolerate on a continuous trickle basis. I'd bet it cannot keep up with the battery's self-discharge, let alone overcharge it.

thank you for your reply. if I charge my 3.7v lipo battery with 1v to 2v will it work? will this small voltage be able to charge up the lipo battery?

 

thank you for your reply. if I charge my 3.7v lipo battery with 1v to 2v will it work? will this small voltage be able to charge up the lipo battery?

As others have pointed out the issue isn't the voltage it's the current. For example a 18650 lithium cell (commonly found in laptops) have a nominal charging current of 0.5A for a single cell.

Download the datasheet of the battery you want to use and find the nominal charging current you need to charge the battery. Then figure out how much current you can source from the Piezo element, and compare it with the charging current. Then you will understand how feasible your project is. I doubt you will be able to power a microcontroller with this idea.

It's a fun project but if you can't charge a LiPo, or power an arduino directly perhaps you could use a supercap to store the charge for a short amount of time to power something else? Like a few LED's?

 

risk of that? I suspect that

As others have pointed out the issue isn't the voltage it's the current. For example a 18650 lithium cell (commonly found in laptops) have a nominal charging current of 0.5A for a single cell.

Download the datasheet of the battery you want to use and find the nominal charging current you need to charge the battery. Then figure out how much current you can source from the Piezo element, and compare it with the charging current. Then you will understand how feasible your project is. I doubt you will be able to power a microcontroller with this idea.

It's a fun project but if you can't charge a LiPo, or power an arduino directly perhaps you could use a supercap to store the charge for a short amount of time to power something else? Like a few LED's?

I plan to store the energy in Lipo Battery 3.7V 500mAh battery. Is it possible to charge it with 1v to 3v only?

 

I plan to store the energy in Lipo Battery 3.7V 500mAh battery. Is it possible to charge it with 1v to 3v only?

Download the datasheet of the battery you are using and that will have all the answers you want. You have to charge litium batteries with a constant current and a constant voltage, characteristics differ between cell types. I can't tell you what you want to know because the information is in the datasheets (which I would download and read myself if I knew the exact manufacturer and type of battery I wanted to use in my project).

Here is a brilliant video from GreatScott on youtube which should educate you a bit further about lithium batteries. (5mins)

Here is another video from Dave Jone's EEVBlog, which is 13mins long:

At least take 20mins to watch those videos, download the datasheets, read the datasheets. After that if you still have questions or if you are stuck come back and post, and someone will be happy to help

 

thank you for your reply. if I charge my 3.7v lipo battery with 1v to 2v will it work? will this small voltage be able to charge up the lipo battery?

No, not without a voltage boost. A lipo battery cannot survive being taken that low in voltage. I don't know what the low limit is but it's well above 2V.

What you are trying to do is called "energy harvesting" and there are integrated circuits available to do this as efficiently as possible. I recommend you take a look at those. But they're not magical. You still have the problem that the energy from your source is minuscule compared to the battery and the load you want to power.

My advice is to do the exercise on paper first, starting with an energy balance. How much does the load need, what are the losses along the chain, what is the source capable of, and so on. Then we can start to design the process and select components.

 

It would also be more feasible, or at least less unrealistic, if you were dealing with a microprocessor that was optimized for low power use. Arduino boards tend not to be optimized for that. If you had a purpose built low power board layout for a chip that's specifically optimized for low power consumption, then it wouldn't take us much energy to keep the thing running. The MSP430 is the only one I know personally, but I'm sure there are lots of options

It might also be good to consider more effective ways of harvesting the energy from walking. Piezos are quite limited! Maybe you could take the mechanism from a self winding watch and convert its mechanical energy into electrical energy somehow. I don't know - this is above my pay grade!

 

Maybe you could take the mechanism from a self winding watch and convert its mechanical energy into electrical energy somehow.

Something like this but on the bottom of your shoe?

 

i will use this 3.7V battery with charging protection chip inside it.
https://www.ebay.in/itm/172783446221?aff_source=Sok-Goog
I think it would work with the same rest circuit.

 

It appears that you aren't going to listen to anyone that is trying to point to the great, big, white elephant in the room, are you?

Based on that school project, you would need to walk to the moon and back three times to charge a cell phone battery one time.

 

It appears that you aren't going to listen to anyone that is trying to point to the great, big, white elephant in the room, are you?

Based on that school project, you would need to walk to the moon and back three times to charge a cell phone battery one time.

No sir, It is not like that I am taking all your suggestions seriously and with respect. what I want to do is basically, I want to show that the battery(3.7v rechargeable battery) has started to charge. I don't want to charge the battery completely. I know that it is not possible. I want to give power to the MSP430 only to take readings from the sensor and light and light LED's based on the ambient temperature. after that I will recharge the battery aging and than again sense the temperature.
if it would not work than this would be a result.

 

Pavegen - a brilliant piece of green-energy marketing hype with no chance of being anything other than a "talking point" for the latest public green energy snow job.

Show me the cost per watt please!

Why do "science communicators" insist on pushing this stuff that is just feel-good silliness?

 

Pavegen - a brilliant piece of green-energy marketing hype with no chance of being anything other than a "talking point" for the latest public green energy snow job.

Show me the cost per watt please!

Why do "science communicators" insist on pushing this stuff that is just feel-good silliness?

Funny, alot of nay-sayers said the same about solar when the cost of coal per watt was much cheaper!

Nobody is expecting it to replace a nuclear power station anytime soon. At the moment its a novel application for powering ticket machines in train stations with the added value of collecting data about passenger footfall.

Economically i accept it's only worth what people agree to pay for it. But like solar if you give something a chance, you never know what breakthroughs in science will make something economically feasible in the future

 

I want to give power to the MSP430 only to take readings from the sensor and light and light LED's based on the ambient temperature. after that I will recharge the battery aging and than again sense the temperature.

Ok I'm confused. At the start you wanted to charge a mobile phone with energy harvested from walking. Now you want to power a micro-controller, take ambient temp measurements and light an LED according to temperature?

Is this correct? If so you could just power all that off alkaline batteries. Why use a piezo element at all?

In summary, is your goal now either to measure things and light an LED or is it to harvest energy from the piezo?

Edit:
The piezo idea would still be worth doing for your own education. It might never charge a mobile phone but the process of making the calculations looking at datasheets etc will be really beneficial and you will learn alot.

 

when the cost of coal per watt was much cheaper!

Ok I'm confused. At the start you wanted to charge a mobile phone with energy harvested from walking. Now you want to power a micro-controller, take ambient temp measurements and light an LED according to temperature?

Is this correct? If so you could just power all that off alkaline batteries. Why use a piezo element at all?

In summary, is your goal now either to measure things and light an LED or is it to harvest energy from the piezo?

Edit:
The piezo idea would still be worth doing for your own education. It might never charge a mobile phone but the process of making the calculations looking at datasheets etc will be really beneficial and you will learn alot.

Idea is same it's just that I want to make some practical use of that energy generated from the piezo electric crystal. what I mean to say that, using piezo small embedded systems with low power requirements could be made.
I have not given up that idea of phone charger. I will definitely work for it. it is my final main project for personal use. but project with MSP430 I have to submit in college.
I don't want to charge my phone 100%, I want to show that it can be used to even start the charging of phone. piezo is capable enough for charging a mobile phone.