Piezo Energy Harvesting LTC3588-1 - Page 1
Forum section: electronics / projects

author: K1JOS
author_rank: Regular Contributor
timestamp: December 30, 2017, 08:12:38 pm
content: I am helping my granddaughter with a high school science project. She and her partner want to demonstrate the harvesting of piezo mechanical energy into electric energy to charge a low capacity AA NiMh battery. There are many available small (0.5” x 2”) piezo sensor strips that suit this purpose. These piezo film strips ideally need to be flexed at a rate of 20-500 Hz to get near the films resonance frequency to get optimal power transformation. But for now, I built a test jig with a stepper motor that will flex this piezo strip about 5 Hz and after I work out the measurement circuit I will replace the stepper with a DC motor/driver that can get closer to the resonant frequency.I can capture the piezo AC waveforms (40-100 Vpp using a low impedance 50 ohm short coax with alligator clips and my scope set for 50 ohm) on my scope with this setup but now I want to get a quantitative measurement of the current. As I have been reading, if I could drive the motor near the resonant frequency, then such a small film strip could generate 5 mA at 20Vpp. Since my setup will not get to these speeds, current per cycle will likely be in the nA range per cycle. I need to rectify and store enough energy up to some measurable threshold where I can then measure the current across a resistive load repeatedly or perhaps a actual battery charging circuit I came across the LTC3588-1for “Nanopower Energy Harvesting Power Supply” and this is specific for piezo’s but like all opamps, the Piezo voltage cannot exceed the Vin. Vin for the LTC3588 is rated at 20V ( DC) but the Piezo can easily generate >35Vrms. The LTC3588 chip seems not to be stocked by Mouser or Digikey but they have an expensive Demo board. I don’t want to fry the board on first use. Any advice how I could limit the piezo input Voltage (ac) without sacrificing too much of the power?Happy New Year !!Jerry NY2KW

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: December 30, 2017, 09:29:11 pm
content: Piezo devices are pretty much dreadful at energy conversion. If you load them with anything, say an energy harvesting IC, the voltage output will be limited to a safe value as soon as the chip uses the energy- unless you hit it with a hammer. PVF film is particularly bad, though it makes a great sensor. I used the LT chip some time back and there was never any danger of damaging it. Most "tiny" harvesters have to do a lot of harvesting before enough energy gets stored to do anything useful. And that "anything" needs to be brief, say flashing an LED or outputting an RF pulse. To get useful energy, find a glued up bimorph. Glue a weight on the end to make it resonant at some frequency where you have some vibration, maybe 60, 120 or 3600 Hz- look at the rotation speeds of blowers and small motors. Note that the fixed end had to be held very rigidly. They're also fragile, so limit the motion with some bumpers.https://www.steminc.com/PZT/en/piezo-bimorph

author: K1JOS
author_rank: Regular Contributor
timestamp: December 30, 2017, 09:34:07 pm
content: Thanks for great start, the TVS's sound like the easiest and quickest solution to test. Like many high school - grandparent interactions, the request for my help came late and time frame is 3 weeks to generate at least some data. I checked and Arrow does have them in stock. The project is intended to reproduce an experiment done at MIT about 20 years ago where they placed ceramic and film piezo transducers inside a pair of shoes. The whole system, including the power conditioning circuitry and storage elements, was shown to provide 1.3 mW continuous power from a walking speed of 0.8Hz (= brisk walk not fast walk). Unfortunately the details of the power conditioning / storage circuits were not detailed. Therefore, the rate of flexing/compressing the Piezo element in our test jig should not come into the more desirable sub-acoustic resonance range but at about 1 Hz only.Happy New YearJerry

author: Howardlong
author_rank: Super Contributor
timestamp: December 30, 2017, 10:11:22 pm
content: Although I haven’t used the Piezo harvesting section, I have used a demo board Linear produce which contains a schematic. It’s included as part of a collaboration with Wuerth and Silabs:http://cds.linear.com/docs/en/demo-board-manual/DC2080AF.PDFhttps://www.we-online.com/web/en/index.php/show/media/07_electronic_components/produkte_3/energy_harvesting/Broschuere_EnergyHarvesting_105x148_6-Seiter_S_E-IC-744885_121005.pdfThey unforunately don’t include a piezo device for connection in the kit, but the LTC3588-1 device data datasheet mentions the MIDE V21BL directly across the PZ pins. This piezo device data sheet is here but may be obsolete:http://www.mouser.com/ds/2/606/mide%20technology_volture_datasheet_001-1214898.pdfOn the demo board schematic it warns <18v limit to 50mA, >18v limit to 5mA.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: December 31, 2017, 05:11:22 pm
content: I can see getting some power out of a shoe, as you have pretty good force and travel to work with. It would be interesting to do a multi-layer PVF stack, though getting the electrodes hooked up is usually a problem. PZT ceramics probably get you more, if you can protect them from fracture.