How to, Ultrasonic humidifier - Will it help water arc experiments????

[Kator01]

hi djzissis,

you will get a transducer including driver here :

http://www.quick-ohm-piezo.de/index.html

Quickohm is a german company but you can just write them in english.
This is the one you can see at ebay.

One remark on the driver-circuit :

Ultrasonic piezo- transducers are powered wihin a analogue-circuit beeing part of an oscillator. They are not externally driven by a chip like the one posted above. The reason is the electrical property of the piezo-transducer
beeing a capacitor. So this capacitor-property is used in implementing the transducer as part of an LC-Resonat circuit which automaically adapts itself to its inherent resonance thus delivering best output characteristics.
They are running in a slightly distorted sinus-mode.
I have made the effort some time ago to analyse an older type of Honeywell-Bull humidifier and I have to search on my computer if I can find it to place it here as attachement. It was a lot of work to analyse it and make it work.

One transducer-disc is not very strong. They have a power-consumption of about 30 Watt which eaquals not the ultrasonic power. This is much lower. However you can by triple or even five - disc-transducers with 90 - 100 Watt power-consumption.
The quickohm-company sells it. You have to ask about it, it is not listed on their homepage.
You have to ask for "Tauchvernebler" as this is the german term for it.

Regards

Kator01

[Yucca]

Kator is correct about piezo being capacitive element and of course building an analog oscillator around the piezo C would be the cheapest way of doing it.

But you can also drive piezo efficiently from a square wave sig gen clocking a FET:

The secret for max efficiency is to make an LC tank using the piezo as C and then calculate L to give a resonant freq that is the same as the mechanical resonant freq of the piezo in water then you will get max efficiency when you hit this tank with your square waves at that resonant freq.

The C and mechanical resonance freq in water is usually stated in the piezo specs. Eqn for freq of an LC tank is attached as piccy below.

Provided you use an array of the same transducers then of course you can have a FET for each piezo and drive all the FET gates from one oscillator. You could probably even get away without using a FET driver IC between the oscillator and FET because you won´t need fast rise and fall times to hit the tank with.

Yucca.

[Kator01]

Yucca,

LC-Piezo-circuits have just LC-resonance but not a specific resonance related to this LC-circuit in water.The reason is that only one surface of the capacitor ( piezo)  is in contact with water and this surface is not conductive. . If you would immerse the whole LC-Circuit into water ( which is not the case ) than the change of the dielectric-constant  ( 80 for water) would change the wavelenght but not the frequency.
But this is just theoretical as the circuit will not run under water, because it would short out.  Usually these piezos run at 1.3 Mhz.

No problem, you can drive it with a rectangular wave but the disadvantage is that you will have to retune it from time to time as the piezo is changing its capacitance because heating up while working or just by of aging.
It does not save you the proper LC.-Calulation anyway.
Square-wave-driver is a waste of energy because once you hit the resonance it is not a squarewave any longer.
But the FET is getting more strain and will heat up unnecessarily.

Kator

[Yucca]

Thanks kator,

I know what you mean about sharp squares wasting energy in the FETs when driving a resonant system, maybe a low pass filter between the square generator and the FET gate might help soften it up a little.

(Q)
So the piezo oscillator circuit, does its freq drift around to always hit resonance using somekind of feedback to pull the oscillator up or down in freq?

Yucca.