Piezoelectric Magnet Fanner Generator

[lumen]

That's an interesting animated gif. It looks like the field inverts as it passes the large magnets.

I do still have a stack of about 50 piezo disks and the small magnets also. I put the tiny full wave rectifiers somewhere so they wouldn't get lost, so now they are really lost.

Yes, I do have all the parts somewhere.

The piezo disks are real cheap on Ebay and the magnets are small so they are not expensive either.
The rectifiers are SMD and are tiny and only rated to 25v. I figured this was ok as long as they are connected to a capacitor and you never let it charge above the rated 25v max.
They would restrict the high voltage output of the piezo disks by keeping both cycles of the disk charging the capacitor and the disks output could never exceed the voltage on the capacitor.

I may still get back to it some day, or not, so I thought I would pass along anything you might want to use, or not.

[Low-Q]

@ lumen


If you use the gentle and gradually force from the magnet, the output voltage from these piezo discs are not going very high. It is the short lasting high forces that will probably destroy your rectifier.
I have a load of these discs myself. I have tried to stack 20pcs and used a gentle force to compress them. The output voltage isn't that high. However, if I apply a shock of force on them, I can see a small spark through the air.


If I just remember where I put them, I can try to replicate this experiment and post on youtube.


Vidar

[Low-Q]

I found the discs. One complete package of many.
When I stack them and measure voltage. Just by pressing on all of them I measure approx 4-5 Volt. Using the Ampére meter I measure not more than a few micro Ampéres. So there is not much energy in these discs. The voltage drops to 0.2-0.3 volts just by touching each pole. The reason is that they do not compress much. They are in fact made of metal and crystals that isn't all that easy to compress into any significant displacement. So at great force, the displacement is so small that the total energy will be very very low. We talk about not more than a few micro Watts.


If I take only one, and bend it gently, but rapidly to each side, the pressure/stress on the crystal is much greater, so I measure also 4-5Volt, but the Ampéres does not exceed 20uA.


Displacement also means that the magnets must displace the same. That again means that the magnets must provide energy into the discs in order to get anything out. As I see it, the energy output is too low and the efficiency is very low.


Vidar.

[lumen]

@ vidar

I have done some tests on the disks and the best is either to bend them slightly or support the edges and apply presure at the center, but to compress them does not work as well.
They make them with the crystal structure in the direction that is required for optimal use. So these flat disks I believe were intended as buzzers so the movement is likely to be in the diameter direction and say only in the X direction and not radially. So to get the maximum power it would be best to test each one by holding one half and flexing the the other half up and down, then rotating a bit and flex it again until you find the crystal direction for each disk.

This is about when I thought this project may be too complicated and would need some amount of design to make it work well.

The crystals also have a resonate frequency and to optimize the project it might become necessary to test this frequency and use only crystals that have nearly the same resonate frequency since this would be the point with the highest output.

In any case, connecting a single crystal to a full wave rectifier and a capacitor yeilds a surprisingly fast charge for each flex. You can connect a meter to the capacitor and flex it to watch it charge.

It's still an interesting but complicated project that someone should build as long as they understand all the complications.