Instructables
Picture of Piezoelectric Energy Harvester
**Patent Pending - United States 61928067**

Introduction


What is piezoelectric energy harvesting?
Piezoelectricity translates to “electricity from pressure.”  The prefix piezo in Greek means to press or squeeze.  Piezoelectric materials exhibit the piezoelectric effect.  This allows a mechanical force to be applied to the material to deform it slightly and the material will produce an output electric power.  This is done by rearranging the dipoles of the piezoelectric material.  This rearrangement causes a change in the dipole density and therefore a change in the electric field between the dipoles.  Because of this change in the electric field, the piezoelectric material produces an output electric power.

What will be accomplished in this Instructable?
Completion of this Instructable will result in a piezoelectric energy harvesting "boot."  With use of other electronic components, this unit will be able to power other small devices that have a low power consumption.  Total project cost (for 1 unit) is ~ $100.
 
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Step 1: Decide what size the unit should be. Draft it in a CAD program, both in 2D and 3D.

Picture of Decide what size the unit should be.  Draft it in a CAD program, both in 2D and 3D.
base plate 2D dimensioned.png
When drafting, be sure to know the size of the piezoelectric disks that will be used.  Consider spring placement and sizes of springs.  The springs that were used in this unit were about 1.5cm in diameter.  Think ahead to all aspects of design from disk placement, spring placement, to where guide bolts will be placed and connecting bolts will be placed.  Also think about wire management.  The wires can sit next to the disks, but it doesn’t look neat and clean.  It will be helpful to see all of this digitally when it comes to assembling the unit.
BRAINDISIS2 months ago

Where do you buy those piezo electric generators?

kintekobo1 year ago
One small point which occurs to me which could affect the efficiency. If you have connected the piezo units directly in parallel are you not losing power due to the output of one of unit driveing the other units if there is a difference in the phase of the voltage being created? Only if pressure was applied absolutely parallel to all devices would they all produce in phase. Or did this have little effect in practice?
rtingley (author)  kintekobo1 year ago
kintekobo,

It is extremely likely that your hypothesis is correct. Pressure is not (though pretty good considering design constraints) applied absolutely parallel to all disks at the same time. Therefore, it is just about given that the devices are not in phase. This is likely a major part of the lack of efficiency of the unit. I believe that another major problem is the gauge of wire that was used to connect all of the disks in parallel. It is much larger in diameter than the wires coming off of the disks, which means that a lot of power is probably lost to resistance in the circuit. At the the time of testing the unit, I did not have the tools to measure whether the devices were in phase or not, so I cannot conclude that this is a definite issue, though as previously discussed, quite likely so. Given the lack of measurement tools, I concluded that power was lost mainly due to resistance.

Thank you for your ideas - they will be considered when making improvements to the device!

Ryan

Would love to know if you made any improvements, Ryan. I think this could be a really cool submission for good.is' Nest challenge. Let me know if you apply at community@goodinc.com http://homeplanet.maker.good.is/

moghadasi1 year ago
How much electricity by one pizo is produced?
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rtingley (author)  moghadasi1 year ago
I cannot remember the current produced from one disk... I think it was about 30V and low milli- or high micro-amps. I have some data in my .PDF about the project. Unfortunately, I did not have enough time to take and record good data for this unit, though it was not required for the project anyway. I will try to gather some data in the near future as this is a common inquiry.
Kiteman1 year ago
What was the final output?

Did it actually work as a boot sole?
rtingley (author)  Kiteman1 year ago
Please see above reply to rimar2000 for your first question.

The device was indeed tested as a "sole" of a shoe. It was placed on the floor and stepped on to mimic walking. Velcro straps or some other means of attachment to the foot or shoe could be put on the unit to actually use it while walking. With an increased price and some design considerations to make the unit smaller, it could actually fit into the sole of a shoe AND have a larger output.
So, in it's current form, it's more useful as an energy-harvesting floor - put it under a panel in the floor of a corridor?
rtingley (author)  Kiteman1 year ago
Yes, that would be a more plausible application of the existing unit. To operate as a "shoe" or shoe sole, the unit would have to be smaller. The large size of this unit reduces cost as well as exaggerates operation for comprehension of the concept of piezoelectric energy harvesting for the non-scientific minds.
rimar20001 year ago
This is a very useful project, but the main question is ¿is it useful? ¿How many Volts x Amps it brings?
rtingley (author)  rimar20001 year ago
This is a low power source. With a good strike, each disk produces about 25 volts. I do not have my research papers with me at this time and do not recall amperage, though it is in the range of single-digit mA or high uA...In other words, very low current. Many disks together can provide enough power to light a hallway. You may find the file on page 12 entitled "JR-EAST.pdf" to be helpful in answering this question.
kardinal71 year ago
No video? You should make a video.