On Wed, 2 Dec 1998, Sten Dahlgren wrote:

> I suppose they don't like anything else than sine waves to.

The piezos are usually one of the capacitors in a LC resonant circuit,
whose L is the secondary of a transformer driven by the switcher.

> > A 50 Watt input cleaning vat takes about 2 liters of liquid for jewelry,
> > diamonds etc. cleaning (mild cleaning). For carbs you might want ten times
> > as much power.
> >
> Up to 5 liters is what i have in mind. I don't think 50mm piezo's would
> be enough
> for this level of power.

No. The 50mm piezos will drive up to about 10Watts iff loaded (else they
exfoliate earlier). I think that you can make a very small cleaning vat
with one of these. There was a project in a French Mag: Electronique
Pratique. It was not the real thing re: power imho. It used a 50mm disk
and a cup-sized vat with less than 2W input (imho). It had lots of
'educative' timers etc around the actual driver.

> Do you know what voltage levels is used ?
> I think they need sinewaves to.

The sine results from the resonance but it must not be sine. Noise is
better ;) The voltage can reach 3-4kV pk-pk unloaded in a 20Watt unit.

Notice that I keep saying 'loaded'. NOTICE that please. Unloaded drivers
die early unless you have some sort of power feedback. Also, none of these
operate at a constant frequency, they rather let themselves be 'dragged'
by the resonance of the vat, or are frequency or noise swept, which
results in a frequency modulation / noise that moves the nulls in the
standing waves produced in the vat all the time. It also makes an
incredibly unbearable noise (the neighbor is a jeweller and he has one of
these running all day long - I can hear it even through 2 walls).

One interesting thing to try out is to get one of those piezo sirens for
alarms (the kind that has a plastic nut screwed onto the body for panel
mount, and is water-proof), and mount it in the bottom of an empty
aluminium can (w/o lid), after removing the electronics to gain access to
the bare driver. It should withstand water well enough for a while,
especially if siliconed into the hole. I suppose that the water will raise
the resonant frequency from about 3-5 kHz nominal but I don't know how
high.

Basically an ultrasonic cleaner that does not achieve the energy density
required for cavitation to occur in the cleaning liquid will do nothing at
all except kill your ears slowly. Also the higher the frequency the better
it gets at the dirt (within reason), or so the books say.

Last: It seems that it is possible for hollow bodies (such as carbs ?) NOT
to be cleaned properly in a normal cleaner on account of the walls of the
body acting as lenses/shields for the acoustical waves. f.ex. hydraulical
lines are cleaned by 'shining' ultrasound directly into the tube, through
circulating liquid under pressure, instead of putting the tube in a
cleaning vat.

sorry for the long posting,

Peter