Ultrasonic cleaner...

[Don Y]

I rescued an ultrasonic cleaner which, of course, \"has issues\".
The bath is large enough that we could use it to clean the shower
heads of their \"hard water deposits\"...

Assuming the transducers (3) aren\'t cracked (in which case
it\'s not worth my effort to pursue a \"cheap\" repair), I\'m
assuming there\'s a step up stage that delivers the excitation
to them? So, this might be a source of a shared failure.

[If the failure is in the \"control circuit\", I can easily
troubleshoot that]

What do the transducers look like, electrically?

And, what sort of potentials am I likely to see across them?

 

[amdx]

On 7/29/2020 3:32 PM, Don Y wrote:

I rescued an ultrasonic cleaner which, of course, \"has issues\".
The bath is large enough that we could use it to clean the shower
heads of their \"hard water deposits\"...

Assuming the transducers (3) aren\'t cracked (in which case
it\'s not worth my effort to pursue a \"cheap\" repair), I\'m
assuming there\'s a step up stage that delivers the excitation
to them?  So, this might be a source of a shared failure.

[If the failure is in the \"control circuit\", I can easily
troubleshoot that]

What do the transducers look like, electrically?

And, what sort of potentials am I likely to see across them?

Somewhere between 2500pf and 7000pf and 10 to 25 ohms resistance.

Of course you tune out the capacitance with an inductor and are left with

driving an ~ 20 ohm resistor.

 I might add that is at anti resonance, at resonance the impedance is
so high it is hard to get any power into it.

I think I have seen it mentioned that it a Royer circuit is used, but I
will disavow all mention of that if it is not true!

When I was in such a business we used a class E amplifier. (at 660kHz)

                                                 Mikek




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[Phil Hobbs]

On 2020-07-29 18:38, amdx wrote:

On 7/29/2020 3:32 PM, Don Y wrote:
I rescued an ultrasonic cleaner which, of course, \"has issues\".
The bath is large enough that we could use it to clean the shower
heads of their \"hard water deposits\"...

Assuming the transducers (3) aren\'t cracked (in which case
it\'s not worth my effort to pursue a \"cheap\" repair), I\'m
assuming there\'s a step up stage that delivers the excitation
to them?  So, this might be a source of a shared failure.

[If the failure is in the \"control circuit\", I can easily
troubleshoot that]

What do the transducers look like, electrically?

And, what sort of potentials am I likely to see across them?

Somewhere between 2500pf and 7000pf and 10 to 25 ohms resistance.

Of course you tune out the capacitance with an inductor and are left with

driving an ~ 20 ohm resistor.

 I might add that is at anti resonance, at resonance the impedance is
so high it is hard to get any power into it.

I think I have seen it mentioned that it a Royer circuit is used, but I
will disavow all mention of that if it is not true!

When I was in such a business we used a class E amplifier. (at 660kHz)

                                                 Mikek

Where the distinction is made,

Antiresonance = parallel

resonance = serial

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Phil Hobbs]

On 2020-07-29 18:45, Phil Hobbs wrote:

On 2020-07-29 18:38, amdx wrote:
On 7/29/2020 3:32 PM, Don Y wrote:
I rescued an ultrasonic cleaner which, of course, \"has issues\".
The bath is large enough that we could use it to clean the shower
heads of their \"hard water deposits\"...

Assuming the transducers (3) aren\'t cracked (in which case
it\'s not worth my effort to pursue a \"cheap\" repair), I\'m
assuming there\'s a step up stage that delivers the excitation
to them?  So, this might be a source of a shared failure.

[If the failure is in the \"control circuit\", I can easily
troubleshoot that]

What do the transducers look like, electrically?

And, what sort of potentials am I likely to see across them?

Somewhere between 2500pf and 7000pf and 10 to 25 ohms resistance.

Of course you tune out the capacitance with an inductor and are left with

driving an ~ 20 ohm resistor.

  I might add that is at anti resonance, at resonance the impedance is
so high it is hard to get any power into it.

I think I have seen it mentioned that it a Royer circuit is used, but
I will disavow all mention of that if it is not true!

When I was in such a business we used a class E amplifier. (at 660kHz)

                                                  Mikek


Where the distinction is made,

Antiresonance = parallel

resonance = series


Cheers

Phil Hobbs



--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Joe Gwinn]

On Wed, 29 Jul 2020 13:32:57 -0700, Don Y
<blockedofcourse@foo.invalid> wrote:

I rescued an ultrasonic cleaner which, of course, \"has issues\".
The bath is large enough that we could use it to clean the shower
heads of their \"hard water deposits\"...

Assuming the transducers (3) aren\'t cracked (in which case
it\'s not worth my effort to pursue a \"cheap\" repair), I\'m
assuming there\'s a step up stage that delivers the excitation
to them? So, this might be a source of a shared failure.

[If the failure is in the \"control circuit\", I can easily
troubleshoot that]

What do the transducers look like, electrically?

A big ceramic capacitor, resonanted with an inductor.


>And, what sort of potentials am I likely to see across them?

I have an old Branson. It has 700 Vac peak to peak across the
transducer. This exceeds the capability of many scope probes, so it\'s
best to make a voltage divider with resistors and capacitors, unless
you have a HV probe.

There was no AC power transformer, so an isolation transformer is
essential for working on such a unit. Then, you can ground whatever
part of the circuit is convenient.

Joe Gwinn

 

[Ricketty C]

On Wednesday, July 29, 2020 at 6:45:35 PM UTC-4, Phil Hobbs wrote:

On 2020-07-29 18:38, amdx wrote:
On 7/29/2020 3:32 PM, Don Y wrote:
I rescued an ultrasonic cleaner which, of course, \"has issues\".
The bath is large enough that we could use it to clean the shower
heads of their \"hard water deposits\"...

Assuming the transducers (3) aren\'t cracked (in which case
it\'s not worth my effort to pursue a \"cheap\" repair), I\'m
assuming there\'s a step up stage that delivers the excitation
to them?  So, this might be a source of a shared failure.

[If the failure is in the \"control circuit\", I can easily
troubleshoot that]

What do the transducers look like, electrically?

And, what sort of potentials am I likely to see across them?

Somewhere between 2500pf and 7000pf and 10 to 25 ohms resistance.

Of course you tune out the capacitance with an inductor and are left with

driving an ~ 20 ohm resistor.

 I might add that is at anti resonance, at resonance the impedance is
so high it is hard to get any power into it.

I think I have seen it mentioned that it a Royer circuit is used, but I
will disavow all mention of that if it is not true!

When I was in such a business we used a class E amplifier. (at 660kHz)

                                                 Mikek


Where the distinction is made,

Antiresonance = parallel

resonance = serial

Isn\'t the series circuit where the voltage on the two reactive components is equal and opposite so the voltage across the pair is zero giving a zero impedance.

The parallel circuit has the same voltage on the two elements so the current is equal and opposite meaning no net current flows through them, so infinite impedance.

That would seem to be the opposite of what Mike is saying.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

 

[amdx]

On 7/29/2020 5:45 PM, Phil Hobbs wrote:

On 2020-07-29 18:38, amdx wrote:
On 7/29/2020 3:32 PM, Don Y wrote:
I rescued an ultrasonic cleaner which, of course, \"has issues\".
The bath is large enough that we could use it to clean the shower
heads of their \"hard water deposits\"...

Assuming the transducers (3) aren\'t cracked (in which case
it\'s not worth my effort to pursue a \"cheap\" repair), I\'m
assuming there\'s a step up stage that delivers the excitation
to them?  So, this might be a source of a shared failure.

[If the failure is in the \"control circuit\", I can easily
troubleshoot that]

What do the transducers look like, electrically?

And, what sort of potentials am I likely to see across them?

Somewhere between 2500pf and 7000pf and 10 to 25 ohms resistance.

Of course you tune out the capacitance with an inductor and are left
with

driving an ~ 20 ohm resistor.

  I might add that is at anti resonance, at resonance the impedance
is so high it is hard to get any power into it.

I think I have seen it mentioned that it a Royer circuit is used, but
I will disavow all mention of that if it is not true!

When I was in such a business we used a class E amplifier. (at 660kHz)

                                                  Mikek


Where the distinction is made,

Antiresonance = parallel

resonance = serial

Cheers

Phil Hobbs

 I don\'t know what that means?

But as you go up in frequency you will have a lower frequency resonance
(I referred to it as antiresonance)

and a high impedance resonance (resonance). as shown in the first graph
here,

https://www.designworldonline.com/why-is-resonant-frequency-important-in-piezo-applications/
Mikek

--
This email has been checked for viruses by Avast antivirus software.
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[Phil Hobbs]

On 2020-07-29 19:33, amdx wrote:

On 7/29/2020 5:45 PM, Phil Hobbs wrote:
On 2020-07-29 18:38, amdx wrote:
On 7/29/2020 3:32 PM, Don Y wrote:
I rescued an ultrasonic cleaner which, of course, \"has issues\".
The bath is large enough that we could use it to clean the shower
heads of their \"hard water deposits\"...

Assuming the transducers (3) aren\'t cracked (in which case
it\'s not worth my effort to pursue a \"cheap\" repair), I\'m
assuming there\'s a step up stage that delivers the excitation
to them?  So, this might be a source of a shared failure.

[If the failure is in the \"control circuit\", I can easily
troubleshoot that]

What do the transducers look like, electrically?

And, what sort of potentials am I likely to see across them?

Somewhere between 2500pf and 7000pf and 10 to 25 ohms resistance.

Of course you tune out the capacitance with an inductor and are left
with

driving an ~ 20 ohm resistor.

  I might add that is at anti resonance, at resonance the impedance
is so high it is hard to get any power into it.

I think I have seen it mentioned that it a Royer circuit is used, but
I will disavow all mention of that if it is not true!

When I was in such a business we used a class E amplifier. (at 660kHz)

                                                  Mikek


Where the distinction is made,

Antiresonance = parallel

resonance = serial

Cheers

Phil Hobbs

 I don\'t know what that means?

But as you go up in frequency you will have a lower frequency resonance
(I referred to it as antiresonance)

and a high impedance resonance (resonance). as shown in the first graph
here,

https://www.designworldonline.com/why-is-resonant-frequency-important-in-piezo-applications/

Mikek

Antiresonance = maximum impedance

resonance = minimum impedance

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[amdx]

On 7/29/2020 6:40 PM, Phil Hobbs wrote:

On 2020-07-29 19:33, amdx wrote:
On 7/29/2020 5:45 PM, Phil Hobbs wrote:
On 2020-07-29 18:38, amdx wrote:
On 7/29/2020 3:32 PM, Don Y wrote:
I rescued an ultrasonic cleaner which, of course, \"has issues\".
The bath is large enough that we could use it to clean the shower
heads of their \"hard water deposits\"...

Assuming the transducers (3) aren\'t cracked (in which case
it\'s not worth my effort to pursue a \"cheap\" repair), I\'m
assuming there\'s a step up stage that delivers the excitation
to them?  So, this might be a source of a shared failure.

[If the failure is in the \"control circuit\", I can easily
troubleshoot that]

What do the transducers look like, electrically?

And, what sort of potentials am I likely to see across them?

Somewhere between 2500pf and 7000pf and 10 to 25 ohms resistance.

Of course you tune out the capacitance with an inductor and are
left with

driving an ~ 20 ohm resistor.

  I might add that is at anti resonance, at resonance the impedance
is so high it is hard to get any power into it.

I think I have seen it mentioned that it a Royer circuit is used,
but I will disavow all mention of that if it is not true!

When I was in such a business we used a class E amplifier. (at 660kHz)

                                                  Mikek


Where the distinction is made,

Antiresonance = parallel

resonance = serial

Cheers

Phil Hobbs

  I don\'t know what that means?

But as you go up in frequency you will have a lower frequency
resonance (I referred to it as antiresonance)

and a high impedance resonance (resonance). as shown in the first
graph here,

https://www.designworldonline.com/why-is-resonant-frequency-important-in-piezo-applications/

Mikek




Antiresonance = maximum impedance

resonance = minimum impedance

Cheers

Phil Hobbs

Yes.

Thanks for the correction.

      Mikek


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[Ricketty C]

On Wednesday, July 29, 2020 at 7:33:31 PM UTC-4, amdx wrote:

On 7/29/2020 5:45 PM, Phil Hobbs wrote:
On 2020-07-29 18:38, amdx wrote:
On 7/29/2020 3:32 PM, Don Y wrote:
I rescued an ultrasonic cleaner which, of course, \"has issues\".
The bath is large enough that we could use it to clean the shower
heads of their \"hard water deposits\"...

Assuming the transducers (3) aren\'t cracked (in which case
it\'s not worth my effort to pursue a \"cheap\" repair), I\'m
assuming there\'s a step up stage that delivers the excitation
to them?  So, this might be a source of a shared failure.

[If the failure is in the \"control circuit\", I can easily
troubleshoot that]

What do the transducers look like, electrically?

And, what sort of potentials am I likely to see across them?

Somewhere between 2500pf and 7000pf and 10 to 25 ohms resistance.

Of course you tune out the capacitance with an inductor and are left
with

driving an ~ 20 ohm resistor.

  I might add that is at anti resonance, at resonance the impedance
is so high it is hard to get any power into it.

I think I have seen it mentioned that it a Royer circuit is used, but
I will disavow all mention of that if it is not true!

When I was in such a business we used a class E amplifier. (at 660kHz)

                                                  Mikek


Where the distinction is made,

Antiresonance = parallel

resonance = serial

Cheers

Phil Hobbs

 I don\'t know what that means?

But as you go up in frequency you will have a lower frequency resonance
(I referred to it as antiresonance)

and a high impedance resonance (resonance). as shown in the first graph
here,

https://www.designworldonline.com/why-is-resonant-frequency-important-in-piezo-applications/
Mikek

You said it is hard to get power into the circuit at resonance because the impedance is high. The page you link to says,

Minimum impedance (fm) occurs at the resonant frequency and maximum impedance (fn) occurs at the anti-resonant frequency.

So I think you used the terms reversed.

Not sure what you mean about it being hard to get power into the circuit at the high impedance point, I assume because it is hard to develop any current. How do you get power into a minimum impedance point where it is hard to develop any voltage?

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

 

[John Larkin]

On Wed, 29 Jul 2020 13:32:57 -0700, Don Y
<blockedofcourse@foo.invalid> wrote:

I rescued an ultrasonic cleaner which, of course, \"has issues\".
The bath is large enough that we could use it to clean the shower
heads of their \"hard water deposits\"...

Assuming the transducers (3) aren\'t cracked (in which case
it\'s not worth my effort to pursue a \"cheap\" repair), I\'m
assuming there\'s a step up stage that delivers the excitation
to them? So, this might be a source of a shared failure.

[If the failure is in the \"control circuit\", I can easily
troubleshoot that]

What do the transducers look like, electrically?

And, what sort of potentials am I likely to see across them?

I have seen ICs that specified that they are not to be ultrasonically
cleaned. I think it can break wire bonds.

Probably safe for shower heads!

 

[Don Y]

On 7/29/2020 3:49 PM, Joe Gwinn wrote:

On Wed, 29 Jul 2020 13:32:57 -0700, Don Y
blockedofcourse@foo.invalid> wrote:

I rescued an ultrasonic cleaner which, of course, \"has issues\".
The bath is large enough that we could use it to clean the shower
heads of their \"hard water deposits\"...

Assuming the transducers (3) aren\'t cracked (in which case
it\'s not worth my effort to pursue a \"cheap\" repair), I\'m
assuming there\'s a step up stage that delivers the excitation
to them? So, this might be a source of a shared failure.

[If the failure is in the \"control circuit\", I can easily
troubleshoot that]

What do the transducers look like, electrically?

A big ceramic capacitor, resonanted with an inductor.

That\'s what I thought. How \"lossy\" is the load? I think
this unit is rated ~140W (acoustic)...

And, what sort of potentials am I likely to see across them?

I have an old Branson. It has 700 Vac peak to peak across the
transducer. This exceeds the capability of many scope probes, so it\'s
best to make a voltage divider with resistors and capacitors, unless
you have a HV probe.

I was hoping to avoid probing the transducers directly. I figured I
could isolate the HV and just verify that the *drive* to it was
working properly. I.e., assume transformer and chokes are intact
so if driven correctly but still no apparent output power, the
transducers must be toast.

There was no AC power transformer, so an isolation transformer is
essential for working on such a unit. Then, you can ground whatever
part of the circuit is convenient.

There are at least two xformers (IIRC) in the unit. But, one is undoubtedly
for the controls (MCU/display) and the other likely for the transducer step-up.
ISTM that if the entire unit was behind a transformer, that would likely
be pretty (physically) large -- i.e., I should remember having seen
something like that.

I think I have a 500VA isolation transformer lying around from the days
of designing KWHr meters. That\'s probably about the rated size of this load
(4A @ 120VAC).

The trick will be accessing the electronics without having to do
a major teardown (the insides look like they are pieced together
from lots of \"modules\" instead of designed as an integrated whole)

 

[Bill Beaty]

On Wednesday, July 29, 2020 at 1:33:17 PM UTC-7, Don Y wrote:

[If the failure is in the \"control circuit\", I can easily
troubleshoot that]

A common failure is for water to get past the sealed edge of the steel tub, dribbled down, and perhaps triggered arcing on the transducer plating. Or perhaps ran along a wire and dripped onto the main PCB.

For spontaneous mystery-failures, always (almost always) it\'s just a shorted pwer-FET ...plus whatever else was destroyed during the short. Since the designs usually lack protection against lightning strikes or giant AC line surges, the silicon often dies for no obvious reason.

((((((((((((((((((((((( ( ( (o) ) ) )))))))))))))))))))))))
William J. Beaty . . . . . . . Research Engineer
beaty a chem washingtonEdu . . UW Chem Dept, Bagley Hall RM74
billb eskimoCom . . . . . . . Box 351700, Seattle, WA 98195-1700
ph x3-6195 . . . . . . . . . . http://staff.washington.edu/wbeaty/

 

[amdx]

On 7/29/2020 6:56 PM, Ricketty C wrote:

On Wednesday, July 29, 2020 at 7:33:31 PM UTC-4, amdx wrote:
On 7/29/2020 5:45 PM, Phil Hobbs wrote:
On 2020-07-29 18:38, amdx wrote:
On 7/29/2020 3:32 PM, Don Y wrote:
I rescued an ultrasonic cleaner which, of course, \"has issues\".
The bath is large enough that we could use it to clean the shower
heads of their \"hard water deposits\"...

Assuming the transducers (3) aren\'t cracked (in which case
it\'s not worth my effort to pursue a \"cheap\" repair), I\'m
assuming there\'s a step up stage that delivers the excitation
to them?  So, this might be a source of a shared failure.

[If the failure is in the \"control circuit\", I can easily
troubleshoot that]

What do the transducers look like, electrically?

And, what sort of potentials am I likely to see across them?
Somewhere between 2500pf and 7000pf and 10 to 25 ohms resistance.

Of course you tune out the capacitance with an inductor and are left
with

driving an ~ 20 ohm resistor.

  I might add that is at anti resonance, at resonance the impedance
is so high it is hard to get any power into it.

I think I have seen it mentioned that it a Royer circuit is used, but
I will disavow all mention of that if it is not true!

When I was in such a business we used a class E amplifier. (at 660kHz)

                                                  Mikek

Where the distinction is made,

Antiresonance = parallel

resonance = serial

Cheers

Phil Hobbs

 I don\'t know what that means?

But as you go up in frequency you will have a lower frequency resonance
(I referred to it as antiresonance)

and a high impedance resonance (resonance). as shown in the first graph
here,

https://www.designworldonline.com/why-is-resonant-frequency-important-in-piezo-applications/
Mikek
You said it is hard to get power into the circuit at resonance because the impedance is high. The page you link to says,

Minimum impedance (fm) occurs at the resonant frequency and maximum impedance (fn) occurs at the anti-resonant frequency.

So I think you used the terms reversed.

Not sure what you mean about it being hard to get power into the circuit at the high impedance point, I assume because it is hard to develop any current. How do you get power into a minimum impedance point where it is hard to develop any voltage?

Ya, my point was you need a much higher voltage at anti resonance. I\'ll
just shut up now.

                                                Mikek


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[Don Y]

On 7/29/2020 6:15 PM, Bill Beaty wrote:

On Wednesday, July 29, 2020 at 1:33:17 PM UTC-7, Don Y wrote:

[If the failure is in the \"control circuit\", I can easily troubleshoot
that]

A common failure is for water to get past the sealed edge of the steel tub,
dribbled down, and perhaps triggered arcing on the transducer plating. Or
perhaps ran along a wire and dripped onto the main PCB.

I don\'t see that as being a possibility with this unit. There are no
seams/openings in the tub (other than the drain -- and there don\'t appear
to be any cracks, there). The tub (6L) itself has a lip on all sides that
hangs over the sides of the enclosure (i.e., any overfill *should*
drip onto the tabletop and not run down the sides). And, anything that
did run down the sides can\'t gain entry to the electronics within.

For spontaneous mystery-failures, always (almost always) it\'s just a shorted
pwer-FET ...plus whatever else was destroyed during the short. Since the
designs usually lack protection against lightning strikes or giant AC line
surges, the silicon often dies for no obvious reason.

Yes, I was hoping it would be something along those lines. The \"controls\"
appear to work (on casual observation) so any failure is likely in
the HV section -- or the transducers (e.g., did someone \"run it dry\"?).

But, I have no idea of the device\'s history. It was being recycled for it\'s
scrap metal value and looked like it could potentially be useful (to me).

 

[dcaster@krl.org]

On Thursday, July 30, 2020 at 12:21:02 AM UTC-4, Don Y wrote:

On 7/29/2020 6:15 PM, Bill Beaty wrote:
On Wednesday, July 29, 2020 at 1:33:17 PM UTC-7, Don Y wrote:

[If the failure is in the \"control circuit\", I can easily troubleshoot
that]

A common failure is for water to get past the sealed edge of the steel tub,
dribbled down, and perhaps triggered arcing on the transducer plating. Or
perhaps ran along a wire and dripped onto the main PCB.

I don\'t see that as being a possibility with this unit. There are no
seams/openings in the tub (other than the drain -- and there don\'t appear
to be any cracks, there). The tub (6L) itself has a lip on all sides that
hangs over the sides of the enclosure (i.e., any overfill *should*
drip onto the tabletop and not run down the sides). And, anything that
did run down the sides can\'t gain entry to the electronics within.

For spontaneous mystery-failures, always (almost always) it\'s just a shorted
pwer-FET ...plus whatever else was destroyed during the short. Since the
designs usually lack protection against lightning strikes or giant AC line
surges, the silicon often dies for no obvious reason.

Yes, I was hoping it would be something along those lines. The \"controls\"
appear to work (on casual observation) so any failure is likely in
the HV section -- or the transducers (e.g., did someone \"run it dry\"?).

But, I have no idea of the device\'s history. It was being recycled for it\'s
scrap metal value and looked like it could potentially be useful (to me).

Ebay and Aliexpress sell bare transducers.

Dan

 

[Don Y]

On 7/30/2020 11:00 AM, dcaster@krl.org wrote:

But, I have no idea of the device\'s history. It was being recycled for it\'s
scrap metal value and looked like it could potentially be useful (to me).

Ebay and Aliexpress sell bare transducers.

The device is rated at ~140W (acoustic power). Three transducers.
Assuming no derating, that would be ~50W/each. So, maybe $60+
to buy replacements?

I\'ll just return it to the recycle pile and watch for another
likely candidate (if the transducers are the problem). :>

[It\'s one of those many things that I\'d never *buy* -- but would
gladly *repair* (for little or no cost). Kindof like my laminator.
Or the electric wheelchairs. Or the stereo microscope. Or the 40\"
scanner. Or the B-size flatbed scanners. Or the RLC bridge. Or...]

 

[Joe Gwinn]

On Wed, 29 Jul 2020 17:30:51 -0700, Don Y
<blockedofcourse@foo.invalid> wrote:

On 7/29/2020 3:49 PM, Joe Gwinn wrote:
On Wed, 29 Jul 2020 13:32:57 -0700, Don Y
blockedofcourse@foo.invalid> wrote:

I rescued an ultrasonic cleaner which, of course, \"has issues\".
The bath is large enough that we could use it to clean the shower
heads of their \"hard water deposits\"...

Assuming the transducers (3) aren\'t cracked (in which case
it\'s not worth my effort to pursue a \"cheap\" repair), I\'m
assuming there\'s a step up stage that delivers the excitation
to them? So, this might be a source of a shared failure.

[If the failure is in the \"control circuit\", I can easily
troubleshoot that]

What do the transducers look like, electrically?

A big ceramic capacitor, resonanted with an inductor.

That\'s what I thought. How \"lossy\" is the load? I think
this unit is rated ~140W (acoustic)...

I don\'t recall, but think it is of that order.

And, what sort of potentials am I likely to see across them?

I have an old Branson. It has 700 Vac peak to peak across the
transducer. This exceeds the capability of many scope probes, so it\'s
best to make a voltage divider with resistors and capacitors, unless
you have a HV probe.

I was hoping to avoid probing the transducers directly. I figured I
could isolate the HV and just verify that the *drive* to it was
working properly. I.e., assume transformer and chokes are intact
so if driven correctly but still no apparent output power, the
transducers must be toast.

I don\'t think that not probing the transduced is a successful
approach. This is a power circuit - not too fussy. Just cob togther
a voltage divider.

The frequency will be 30 KHz to 50 KHz, most likely. Won\'t be MHz at
that power level, I\'d guess.

What is the make and model of your unit, anyway?

There was no AC power transformer, so an isolation transformer is
essential for working on such a unit. Then, you can ground whatever
part of the circuit is convenient.

There are at least two xformers (IIRC) in the unit. But, one is undoubtedly
for the controls (MCU/display) and the other likely for the transducer step-up.
ISTM that if the entire unit was behind a transformer, that would likely
be pretty (physically) large -- i.e., I should remember having seen
something like that.

Exactly.

I think I have a 500VA isolation transformer lying around from the days
of designing KWHr meters. That\'s probably about the rated size of this load
(4A @ 120VAC).

I have such a transformer. Tripp-Lite? One must open it up and
disconnect the green ground (and isolate the spade terminal with
plastic tubing).

The trick will be accessing the electronics without having to do
a major teardown (the insides look like they are pieced together
from lots of \"modules\" instead of designed as an integrated whole)

But many more points can be accessed, if only you knew what all those
wires were.

Joe Gwinn

 

[Don Y]

On 7/30/2020 4:53 PM, Joe Gwinn wrote:

On Wed, 29 Jul 2020 17:30:51 -0700, Don Y
blockedofcourse@foo.invalid> wrote:

I was hoping to avoid probing the transducers directly. I figured I
could isolate the HV and just verify that the *drive* to it was
working properly. I.e., assume transformer and chokes are intact
so if driven correctly but still no apparent output power, the
transducers must be toast.

I don\'t think that not probing the transduced is a successful
approach. This is a power circuit - not too fussy. Just cob togther
a voltage divider.

I figure if the primary is being chopped, a lack of output power is
either:
- bad xformer
- bad chokes (all 3!)
- bad xducers (all 3)
In either case, I won\'t dick with it any further. (these sorts of things
turn up fairly regularly so its easier just to wait for another to come along)

The frequency will be 30 KHz to 50 KHz, most likely. Won\'t be MHz at
that power level, I\'d guess.

What is the make and model of your unit, anyway?

<https://www.ebay.com/itm/VWR-Model-150D-Aquasonic-Ultrasonic-Bath-/143178745430>

Apparently it has a different \"part number\" than \"model number\"
so chasing it down on the VWR web site was tedious.

There was no AC power transformer, so an isolation transformer is
essential for working on such a unit. Then, you can ground whatever
part of the circuit is convenient.

There are at least two xformers (IIRC) in the unit. But, one is undoubtedly
for the controls (MCU/display) and the other likely for the transducer step-up.
ISTM that if the entire unit was behind a transformer, that would likely
be pretty (physically) large -- i.e., I should remember having seen
something like that.

Exactly.

Displays blink, buttons seem to be recognized... just no \"bzzzzz\". So, I
assume the controls are working (with possible exception of the interface
to the HV) and the problem lies in the HV section.

I think I have a 500VA isolation transformer lying around from the days
of designing KWHr meters. That\'s probably about the rated size of this load
(4A @ 120VAC).

I have such a transformer. Tripp-Lite? One must open it up and
disconnect the green ground (and isolate the spade terminal with
plastic tubing).

\"Triad-Utrad\". And, apparently only 250VA.

The trick will be accessing the electronics without having to do
a major teardown (the insides look like they are pieced together
from lots of \"modules\" instead of designed as an integrated whole)

But many more points can be accessed, if only you knew what all those
wires were.

Yes, but it\'s a mess in there. Like it was pieced together instead of
being designed as an integrated unit. Like it was designed by someone
in *Detroit* (motor city)!

\"Control processor\" is mounted behind the indicators -- indicators mounted
on the solder side of the (thru hole) board. \"Power\" board mounted on
the base -- with a case-mounted heatsink supporting the switching Q\'s
jutting out over much of the electronics. I.e., if I want to probe stuff,
I will have to remove the boards while staying close to the xducers due to
lead lengths as well as the Qs on the heat sink.

And, of course, ensuring that there\'s water in the tub in case the
thing actually tries to start!

My plan is to trace out the HV section and see how it is gated on/off.
Then, verify the presence of that gate when commanded by the controls.
Then, go looking at the chopper to see if there\'s any signs of life, there.

 

[Tony Stewart]

On Wed. 29 Jul.-20 10:06 p.m., amdx wrote:

On 7/29/2020 6:56 PM, Ricketty C wrote:
On Wednesday, July 29, 2020 at 7:33:31 PM UTC-4, amdx wrote:
On 7/29/2020 5:45 PM, Phil Hobbs wrote:
On 2020-07-29 18:38, amdx wrote:
On 7/29/2020 3:32 PM, Don Y wrote:
I rescued an ultrasonic cleaner which, of course, \"has issues\".
The bath is large enough that we could use it to clean the shower
heads of their \"hard water deposits\"...

Assuming the transducers (3) aren\'t cracked (in which case
it\'s not worth my effort to pursue a \"cheap\" repair), I\'m
assuming there\'s a step up stage that delivers the excitation
to them?  So, this might be a source of a shared failure.

[If the failure is in the \"control circuit\", I can easily
troubleshoot that]

What do the transducers look like, electrically?

And, what sort of potentials am I likely to see across them?
Somewhere between 2500pf and 7000pf and 10 to 25 ohms resistance.

Of course you tune out the capacitance with an inductor and are left
with

driving an ~ 20 ohm resistor.

   I might add that is at anti resonance, at resonance the impedance
is so high it is hard to get any power into it.

I think I have seen it mentioned that it a Royer circuit is used, but
I will disavow all mention of that if it is not true!

When I was in such a business we used a class E amplifier. (at 660kHz)

                                                   Mikek

Where the distinction is made,

Antiresonance = parallel

resonance = serial

Cheers

Phil Hobbs

   I don\'t know what that means?

But as you go up in frequency you will have a lower frequency resonance
(I referred to it as antiresonance)

and a high impedance resonance (resonance). as shown in the first graph
here,

https://www.designworldonline.com/why-is-resonant-frequency-important-in-piezo-applications/

Mikek
You said it is hard to get power into the circuit at resonance because
the impedance is high.  The page you link to says,

Minimum impedance (fm) occurs at the resonant frequency and maximum
impedance (fn) occurs at the anti-resonant frequency.

So I think you used the terms reversed.

Not sure what you mean about it being hard to get power into the
circuit at the high impedance point, I assume because it is hard to
develop any current.  How do you get power into a minimum impedance
point where it is hard to develop any voltage?

Ya, my point was you need a much higher voltage at anti resonance. I\'ll
just shut up now.

                                                Mikek

I think we have always called the RLC parallel tank circuit as a
resonant circuit which is true but for a 3rd order CLC resonant circuit
it is the series lower frequency , low impedance which is called
\"resonant\" which shows an impedance notch and the higher frequency which
is parallel high impedance called \"anti-resonant\". This may have
confused us all at some point and perhaps even me now.

The series resonance draws more current at low impedance but higher
power and is used for ultrasonic imaging and cleaning. The
anti-resonant is not used because it would require much higher voltage
into the high impedance to produce the equivalent power.

Parallel crystal oscillators are more popular because they draw much
less power but as frequency is used above 20MHz in order to reduce the
effects of stray capacitance, series tuned crystals are specified for
oscillators with known ESR\'s.