School Piezo Energy Harvesting Experiment

[boatanchorguy]

Helping my granddaughter with a HS project on the piezoelectric effect and renewable energy.  She placed a 30mm piezo disc under the heel of her sneaker that inputs into a Schottky (1N5711) full wave bridge whose output is across a 47uF 50V electrolytic.   Wearing the PCB with bridge/cap on the outside of her sneaker she walked on a treadmill at a casual rate (1 step/second) and we data logged the slow charge up of the capacitor.  It took just about 7 minutes to plateau at around 5.25 VDC.   Without the capacitor - the open circuit voltage from the bridge is quite high --- 20-60 Vdc but when the capacitor is added it loads down to initially a few mVdc and slowly comes up as the cap is charged by the piezo.  We want to get some estimate of the energy generated per step recognizing this is on the microjoule or nanojoule level.  I was going to use the equation  for stored energy in capacitor  = ½ C x V^2 and divide by total seconds to reach the exponential plateau of the 5.25Vdc maximal charge.  Next step will be to add a tiny LiPo charger or play with the LTC3588 chip.  Any advice on how to get this estimate of piezo power per step would be appreciated.

Thank you in advance

[tggzzz]

Please don't "double post"; it confuses everybody.

I suggest the other post is the better place to respond.