What am I doing wrong with schematic?

Discussion in 'The Projects Forum' started by Uskok, Nov 2, 2015.

  1. Uskok

    Thread Starter Member

    Aug 19, 2015
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    Hello guys... I bought this ultrasonic transducer 60W 40KHz from ebay..

    http://www.ebay.com/itm/High-Effici...340024?hash=item5d4d453638:g:ZxoAAOSwPcVVjkKW

    and using this schematic i connected him

    http://electricstuff.co.uk/levit.html

    But from some reason when everything is connected transducer wont work...
    Except i change the capacitor... Now I am using the 1nF capacitor as from scheme and I got the resonant requency of 39-40KHz, but if I put the 2 or 4nF capacitor the transducer start to produce some squeaky noises. I use the laptop charger as a PSU.

    Why is that so? Could it be transformer or? Maybe transformer can't handle this frequency?

    I hope someone of you will help me..
     
  2. ian field

    Distinguished Member

    Oct 27, 2012
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    AFAIK: you have to include the apparent loss factor in a feedback loop to maintain drive under load. The transducer has a lot in common with a capacitor, so you have a big phase angle to consider to get any "real" power into it anyway - then when you fill the tank with water and add articles to clean, that creates a loss factor which sends the power vector all over the place.

    Silicon chip/EPE published an ultrasonic cleaner, I think they used a PIC to alternate between various frequencies on the basis; "one of those is bound to get it".

    Years ago I was mucking about with what I could connect to an electret capsule JFET and put through a power MOSFET stage, one thing I tried was an ancient STC germanium transistor - it produced fierce noise, so I hooked a large piezo disc from a car alarm on the MOSFET output and fired it up. The piezo disc instantly shattered and crazed. If I'd soldered that to the end of a tin can and loaded it with water, I probably would have had a small but pretty decent ultrasonic cleaner.
     
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  3. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    With the components on the schematic, the frequency range is 25 kHz to 39 kHz. The entire range is less than the 40 kHz rating of the driver, but 39 kHz probably is close enough to see something happen. Increasing C1 decreases the output frequency even more, which is why things did not work when you did that. For a better adjustment range, remove C1 and replace it with two capacitors in parallel - 470 pF and 270 pF. This will put 40 kHz closer to the center of the P1 adjustment range.

    ak
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    If R2 is a 18k, change it to a 12k, then your preset resistor will give you a bigger frequency span.


    40khz is R1 1k, R2 12k +5k with the preset(17k) and 1nF cap
     
    Last edited: Nov 2, 2015
  5. ian field

    Distinguished Member

    Oct 27, 2012
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    The very earliest magazine project ultrasonic cleaner I saw, had a tuneable inductor with a front panel knob. You basically had to put the stuff to be cleaned in it and then tune the oscillator until the water cavitates properly.

    The generators in the bench top tanks made by Kerry Ultrasonics were a very crude form of PLL. The actual generator is pretty much an astable driving a centre tapped transformer primary. The base drive comes from a feedback transformer with a centre tapped secondary - its primary is in series with the transducer.
     
  6. Uskok

    Thread Starter Member

    Aug 19, 2015
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    I figure out if I put a 50K resistor. The transducer starts to produce so loud and squeaky noises...
    If i put water on it I see soo little movements... hmm....
     
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Even though you don't say where you are putting the 50K resistor, it doesn't matter. Read the previous posts. 50K is too large a resistor for this timing circuit if you want a 40 kHz output.

    ak
     
  8. Uskok

    Thread Starter Member

    Aug 19, 2015
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    I was wrong.. I want to mention that I put the 50K potentiometer...
     
  9. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Read post #4 Again
     
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