Problem of Ultrasonic Generator of Nonwoven fabric bag makin machine.

Discussion in 'Electronics Resources' started by Shahed1969, Apr 20, 2015.

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  1. Shahed1969

    Thread Starter New Member

    Apr 20, 2015
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    Dear All,
    These 15kHz ultrasonic generators are rather basic Chinese units (see pictures) used for welding nonwoven plastic (basically thin plastic fabric).
    spare_parts-l.jpg
    Image-01.jpg Image-02.jpg
    Image-03.jpg
    images2.jpg
    This Ultrasonic Generator become faulty, I have medium idea about electronics, but fail to repair it.
    The Chinese manufacture did not give us any circuit diagram, so I made a full circuit diagram and exhibit here for reference.
    Circuit Diagram of Ultrasonic Generator.jpg

    After checking I found some power transistor (2SC3998) faulty on Lord amplifier then changed and found two diode on oscilation PCB then change. After that when I run the machine frequency not matching with ultrasonic transducer and nonwoven fabric soldering not possible.

    If any one familiar with this system please give me the solution.


    Thanks

    Shahed
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    I'm not familiar with the system, but when you say "when I run the machine frequency not matching with ultrasonic transducer" can you tell us what was the measured output frequency and what is the specified transducer frequency?
    Are all the power rail voltages what they should be?
     
  3. Shahed1969

    Thread Starter New Member

    Apr 20, 2015
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    If it will match the frequency then nonwoven welding will be done well, moreover it can be understand by sound of horn.
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Understood, but that doesn't answer my questions ;).
     
  5. Shahed1969

    Thread Starter New Member

    Apr 20, 2015
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    I have no frequency measuring instrument, but manufacturing company said it's output frequency is 15 Khz.
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    I can't work out which components, apart from the 'tuning coil', determine the intended operating frequency. Have you checked the 20uF 450V AC cap near the output transformer?
     
  7. Shahed1969

    Thread Starter New Member

    Apr 20, 2015
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    Yes I have changed the 20uF 450V AC cap, but nothing positive.
    At first two diode burns out at input side of ring type transformer and 5 pcs transistor (2SC3998) ans some resistor burns out at input side of output transformer, then I replace all bad component then when I start the machine frequency comes out but not sufficient for soldering. I tried for frequency tuning by tuning coil, it has a tuning knob which move a core inside the tuning coil then frequency up and down in a limited range but doesn't go in sufficient high for soldering.
    I think it has some technique for fine tuning.
     
  8. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    The circuit appears to be some form of self-resonant arrangement where the transducer itself partly determines the oscillation frequency. Are you sure that the transducer itself isn't damaged/faulty?
     
  9. Shahed1969

    Thread Starter New Member

    Apr 20, 2015
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    Yes! Transducer it self OK. Because when we change the Frequency Generator only then it works properly.
     
  10. sesmd (stan)

    New Member

    Sep 30, 2014
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    Perhaps using an impedance matching transformer between the piezo transducer/pickup and the amp input... i.e. such as a small 8 ohm: 1000 ohm
    audio transformer. Connect the 1000 ohm side across the piezo, 8 ohm side to FET via a DC blocking cap (thus allowing the FET to be properly biased).
    Good luck with your circuit... hope you get it working without any more troubles..

    Addendum... consider using a hi-gain BJT instead of FET, with the transformer mod..
     
  11. strantor

    AAC Fanatic!

    Oct 3, 2010
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    This is an impressive help request post. Rarely does anybody go to the trouble of reverse engineering a circuit and making a diagram before posting. Unfortunately i cannot help, but i just wanted to say "thanks" for not posting a blurry image of a PCB and expecting someone to magically diagnose it from across the internet (most people do that). I'm sure there is someone on this forum who can help, with the information you have provided.
     
    panic mode likes this.
  12. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Check the polyester caps for proper capacitance
     
  13. Shahed1969

    Thread Starter New Member

    Apr 20, 2015
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    I think you are telling about 0.1 mfd (104) capacitor, I will check it.
     
  14. Shahed1969

    Thread Starter New Member

    Apr 20, 2015
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    There is no any FET using in this circuit, using only NPN Transistor (2SC3998).
     
  15. Shahed1969

    Thread Starter New Member

    Apr 20, 2015
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    I have changed the same but nothing positive.
     
  16. Matias Baldo

    New Member

    Jun 3, 2015
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    Hello Shahed, this is the first time I write in this forum. I'm working on the same equipment right now.
    You have saved me a lot of time re drawing the circuit, so thank you.

    I hope that you already solved the problem, if that isn't the case...

    Try to run the generator without the transducter plugged. If it run ok without the overload led turning on it might be working but on a different frequency. You should disassemble the tunning coil and see if the ferrite bars are well fixed on the screw, that is a common problem I found on these generator.

    Thank you again, Matias
     
  17. Shahed1969

    Thread Starter New Member

    Apr 20, 2015
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    Thank you Matias Baldo.
    I have checked the tuning coil and found ferrite core is fixed as well on the screw.

    Now our main problem is every hardware component are OK. But frequency not enough strong to weld the fabric.
    I try to adjust by tuning coil but failed.

    If you are familiar with this unit please share your experience.


    Thanks

    Shahed
     
  18. ScottWang

    Moderator

    Aug 23, 2012
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    Welcome to the AAC forum.

    The owners of All About Circuits has elected not to host discussions of transformerless threads.

    This thread is against the AAC forum rules, Terms of Service (ToS).

    Any kind of over-unity devices and systems
    Automotive modifications
    Devices designed to electrocute or shock another person
    LEDs to mains
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    Transformer-less power supplies
    Terms of Service (ToS).

    Automotive modifications of any kind are strictly forbidden. Therefore, this thread will be closed.

    Please try to understand the reasons behind this action, and feel free to browse and use the forums.

    You might find answers to your questions in one of these forums:

    http://forum.allaboutcircuits.com/showthread.php?t=54400

    Another good forum that shares many of the same membership is http://www.electro-tech-online.com/ .

    Good luck.
     
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