Piezo question

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Thread Starter

Energy forever

Joined Sep 11, 2021
46
I got some piezo discs, hook one up to my multimeter, apply pressure to disc, get voltage, switch over to measure current, get nothing. I repeat same process with a second and third disc, and get same results. Ive seen people use these, not mine, but these same piezo discs to power an led hooked strait up and applying a little pressure. So, i should be getting at least some milliamps, but the meter never goes above or below zero. Its just zero. Not even a flash of a negative sign. What confuses me even more is that i get over 20 volts aka the disc seems to be generating electricity. Is it possible for a piezo disc to generate only voltage and zero current, or are they defective? And no, i did not try them all, only three. All three had same results. Voltage up to 20 some volts and zero current.
 

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Thread Starter

Energy forever

Joined Sep 11, 2021
46
Where, on YouTube? Don’t believe everything you see on YouTube. They don’t work that way, you would have to vibrate it to get continuous output.

Bob
So, you know stuff about piezo discs eh? Not answering the question and commenting about youtubers would be considered off topic and trollish. Can you provide an answer to my posted question or are you going to make it look quite clear to the site you just stopped by to troll by not posting an accurate answer to my question?
 

djsfantasi

Joined Apr 11, 2010
8,075
Have you considered that there may not be an answer to your question?

BTW, attacking another member who is trying to help, is considered rude and trollish. And may dissuade members from replying.

Did you notice the classification under member names? It’s an indication of their level of experience. BobTPH certainly is NOT just stopping by to troll.

Bye
 

Thread Starter

Energy forever

Joined Sep 11, 2021
46
Have you considered that there may not be an answer to your question?

BTW, attacking another member who is trying to help, is considered rude and trollish. And may dissuade members from replying.

Did you notice the classification under member names? It’s an indication of their level of experience. BobTPH certainly is NOT just stopping by to troll.

Bye
Im reporting both of you for not answering the question
 

Ian0

Joined Aug 7, 2020
4,122
Is it possible for a piezo disc to generate only voltage and zero current, or are they defective?
NO - they are not defective. Piezo discs have an output impedance in the MΩ region, and appear as a voltage generator in series with a small capacitor, so they only produce a signal in response to a change of force.
Most would struggle to drive a bipolar transistor - a MOSFET gate is more like the sort of load they could manage.
Think about the amount of power you could get from a moving coil loudspeaker when used as a microphone.
 

Ian0

Joined Aug 7, 2020
4,122
Where, on YouTube? Don’t believe everything you see on YouTube.
Screenshot at 2021-10-04 22-02-54.jpgYou can see the amplifier transistor just below the middle LED, above the buzzer. You never get to see the back of the device in his left hand, presumably that's where the batteries are.
 

MrChips

Joined Oct 2, 2009
25,037
I got some piezo discs, hook one up to my multimeter, apply pressure to disc, get voltage, switch over to measure current, get nothing. I repeat same process with a second and third disc, and get same results. Ive seen people use these, not mine, but these same piezo discs to power an led hooked strait up and applying a little pressure. So, i should be getting at least some milliamps, but the meter never goes above or below zero. Its just zero. Not even a flash of a negative sign. What confuses me even more is that i get over 20 volts aka the disc seems to be generating electricity. Is it possible for a piezo disc to generate only voltage and zero current, or are they defective? And no, i did not try them all, only three. All three had same results. Voltage up to 20 some volts and zero current.
There are three reasons why the piezo discs do not supply current, resistance, resistance, resistance.

Do you recall the issue with a power supply that has high source resistance?

The internal resistance of a piezo transducer is very high. Hence it cannot deliver current.
 

Thread Starter

Energy forever

Joined Sep 11, 2021
46
NO - they are not defective. Piezo discs have an output impedance in the MΩ region, and appear as a voltage generator in series with a small capacitor, so they only produce a signal in response to a change of force.
Most would struggle to drive a bipolar transistor - a MOSFET gate is more like the sort of load they could manage.
Think about the amount of power you could get from a moving coil loudspeaker when used as a microphone.
Makes sense. Seems the case. Ill try to remember you are one of the good ones on here.
 
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