I understand this, but do not understand how that voltage is turned into usable workable energy for devices?

to quote: http://www-mtl.mit.edu/researchgroups/icsystems/pubs/journals/2010_ramadass_jssc_jan.pdf

"One of
the main limitations of existing piezoelectric harvesters is in their
interface circuitry"

 

I gotta go, I'll discuss this more later today, if you don't have your answer by then.

 

bias flip rectifier? wouldnt it be easier and less loss just using a switch to reverse the polarity when it bends and bends back (mechanical rectifier) since piezo generates positive when it flexes one way and negative when it flexes the other?

 

After you rectify and smooth the voltage you might want to look at these two low voltage energy harvesting devices:

LTC3105

LTC3108

 

the potential energy of a piezo crystal that has been deformed is the same as the potential energy when it is relaxed after deforming. squeeze or bend it, voltage apears, relax it, and the voltage dissapears. bend it one way, and the voltage apears, relax it, and the voltage goes away. bend it the other way, and oposite voltage apears, relax it and the voltage goes away.

And what happens if you remove energy by discharging the voltage?

You cannot escape the First Law as you are suggesting.

Overunity does not exist and discussion is forbidden on this forum.

 

it is not overunity, the ieda is to put piezo elements into clothing and use the motion of the wearer generate electricity. not free, just increasing a little the effort put into walking and using it to charge cell phone batteries.

 

You are avoiding my question.

 

Is there a way to transfer high voltage (relative to piezo) like 200 volts, high impedance, into 200 watts?

Anyone have links to certain chapters in the all about circuits ebook that I may further study? Which concepts are the most important to understand for this specific problem?

 

ahash, what have you understood from the answers here?

In particular why are you still asking about 200 watts?

 

sure, just have one amp available. 200 volts with one amp current is 200 watts.
and on the previous when you discharge the voltage, you have no power. you have to keep charging the capacitor in the circuit, or the voltage drops as the current is used.

 

you have to keep charging the capacitor in the circuit

How?

What I am getting at is that it has been stated that merely 'squashing' a piece of piezo material creates a voltage that remains as long as the material remains squashed

If this was the case I could use this to make a perpetual motion machine of the first kind since it would be a limitless source of free energy or overunity.

 

Ok, So far I've understood that:

Watts are a unit of power, not energy. Joules are a unit of energy without regards to time.

Piezos generate unidirectional voltage, unless the source of their mechanical strain is reversing.

The larger the mechanical strain, the larger the voltage. No mechanical strain, no voltage.

The piezo effect generates voltage. To create power from this voltage it has to be hooked up to circuitry which "draws current" (I don't understand that part).

This voltage is dissipated after being used.

---

Many thanks again for your patience in explanation.

 

Mr Chips, this question really ought to be in the Physics section.

ahash, I don't know what stage your education has reached (no disrespect) but can you follow this sequence?

Mechanical work has to be done to distort crystal.

The work enters the distorted lattice as mechanical strain energy.

alphacliff and brownout are correct in saying that is the total energy available.

For certain crystals, called piezo crystals, one result of this distortion is a voltage that develops between the faces of the crystal as the crystal is changing shape.

In order to turn this into usable electrical energy we must use the voltage to pass electrical current through a resistor, where the energy will be changed into heat or through the coils of an electrical motor, where the energy will be changed into the mechancial energy of motion.

Mr Chips has told you the relationships between power, energy, time, voltage and current in electrical terms.

Now for the crystal,
As long as no circuit is connected, the voltage will remain.

but

The voltage will decay as the stored energy is drawn out by connecting some circuit that uses current as I have described. this means the current available will also diminish to zero over time, depending upon the electrical characteristics of the connected circuit.

This must be true, even if we maintain the forces that distort the crystal, since once they have stopped moving (distorting) they have stopped inputting work.

 

in simple terms, when you bend a piezo crystal, a voltage is produced. when you stop bending it, the voltage is no longer produced. when it is allowed to go back to rest state,(nubent) a reversed voltage is produced till it stops unbending.it does not produce a steady state voltage when bent or crushed, it is only while it is being bent or crushed.

 

Go on.
I hope you are not suggesting that a piezo device could contravene the first law?

Not at all. I was responding to the OP's question in #9, suggesting that if he had read and digested your #8, he wouldn't have asked his question.

The piezo effect generates voltage. To create power from this voltage it has to be hooked up to circuitry which "draws current" (I don't understand that part).

This voltage is dissipated after being used.

Sort of. The mechanical strain causes a charge separation very similar to that in a capacitor. Voltage is a measure of the potential energy stored in that separation.

In the analogy to water, the mechanical work is like carrying a bucket of water up the hill. The voltage is the height you raised the bucket. But the energy available also depends on how much water is in the bucket - how much charge is available to flow back downhill.

While water is measured in liters or gallons, electrical charge is measured in coulombs, with 1 ampere being 1 coulomb per second flow rate. Capacitors store charge, and the voltage across a capacitor goes up with the amount of stored charge, in proportion to the capacity of the capacitor, V = F•C, or farads = volts per coulomb.

 

Not at all. I was responding to the OP's question in #9, suggesting that if he had read and digested your #8, he wouldn't have asked his question.

Sorry, mate, I misunderstood.

 

in simple terms, when you bend a piezo crystal, a voltage is produced. when you stop bending it, the voltage is no longer produced. when it is allowed to go back to rest state,(nubent) a reversed voltage is produced till it stops unbending.it does not produce a steady state voltage when bent or crushed, it is only while it is being bent or crushed.

We finally got there!



ahash, since you were unsure about voltage and current do you understand what is meant by capacitance?

 

Studiot, that sequential run down was very helpful. My one question that springs from it is...

In order to turn this into usable electrical energy we must use the voltage to pass electrical current through a resistor

In this case, the electrical current is coming from an outside source?

since you were unsure about voltage and current do you understand what is meant by capacitance?

Capacitance, as I understand it now. Is the build up of voltage inside an object, (e.g. a capacitor) that has two conductive materials separated by a small space?

 

Also, this may seem like another very noob question, but somewhat logical, does a piezo crystal ever "run out" of voltage over time? Or is it just a characteristic of the material that when the crystal structure is disrupted, the voltage is produced, and the effect is constant regardless of how many times it happens?

 

Also, this may seem like another very noob question, but somewhat logical, does a piezo crystal ever "run out" of voltage over time? Or is it just a characteristic of the material that when the crystal structure is disrupted, the voltage is produced, and the effect is constant regardless of how many times it happens?

It more like the material in the crystal starts to fracture and fatigue from mechanical stress over a period of time.

I'm not sure what the lifetime is of energy harvesting types but 'normal' types can be easily damaged from excessive electrical or mechanical stress.

http://www.navsea.navy.mil/nswc/crane/sd18/Public%20Documents/ProductArchive/Crystals.pdf