Quick Question about a Piezoelectric shoe for project

[Jalon Young]

I am currently working on a piezoelectric shoe and the objective of the project is to charge a phone
I am aware a phone is DC
and piezoelectric disc generate AC
I know I need a bridge rectifier to convert
My question is:
Would I generate more volts if I
Use a bridge rectifier to convert AC to DC between each disc
OR
Can I put them in parallel and use 1 bridge rectifier

P.S.
A guy has done this before me and ran into a similar problem and says
"I have found that you can not directly connect the piezoelectric generators in parallel since they create AC current.Although the project will still technically work, this explains the lack of efficiency that everyone (including myself) experienced after making the product. If you are still interested in making the project, I'd recommend trying to use bridge rectifiers for each individual piezoelectric generator, then connecting them in parallel by connecting each all the red wires and all the black wires together in a chain(you might have to also regulate each piezoelectric transducer's output so they have the same voltage and current, but I'm not sure) . It's hard to explain, but if you look up how to wire things in parallel it should make more sense. If you do try wiring each piezo to its own bridge rectifier, be sure to let me know how it goes in the comment section below!I am thinking about updating my instructions for a 2.0 version soon!"
But I find his explanation a bit confusing

 

[berkeman]

Welcome to the PF, @Jalon Young

I think you haven't been getting replies because energy harvesting with piezoelectric film is not a very good match for charging your cellphone. The main issues are power generation (too little per step) and low generated voltages (hence a lot of loss in the conversion up to around 5V DC to charge your phone.

A useful calculation is for you to think of using a different power generation technique attached to the soles of your feet. Maybe some sort of spring-loaded induction coil setup. For each step, calculate how much energy you can extract (force X distance) from the squeezing and extension of the sole with respect to the foot. That will start to give you an idea of whether the power generated is enough to charge your phone in a practical number of steps. For enough displacement (really springy soles), say around 1cm per step, you may well be able to generate enough power. But for piezo film the distance it compresses is very small, like a fraction of a millimeter. So you can see how it would be hard to harvest much energy from compressing a piezo film. (If you only need milliwatts, you might be able to do it with piezo film.)