Mystery transformer

Discussion in 'General Electronics Chat' started by cmartinez, Nov 19, 2014.

  1. cmartinez

    Thread Starter AAC Fanatic!

    Jan 17, 2007
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    Hello, all.

    I have this small transformer that is encapsulated in resin and I can't even tell the wire gauge that's in it, it only has input and output electrodes that I suppose are connected to its windings. My crappy'ol multimeter is telling me that it has an input resistance of about 0.75Ω, and its output resistance is pretty close to that value too... but that could be way off the mark.
    Also... I'd like to avoid dissecting it and ripping its guts apart if that's possible.

    How can I, more or less, approximate what its ratio is, and the inductance on its primary and secondary windings?

    Of course, I've already googled this question (and also searched this forum) and all the answers I got were a little too complicated for my taste.

    Here are (some) of my resources:
    • I don't have a function generator
    • I have a basic (but decent) 2-channel USB oscilloscope
    • I have lots of components available, transistors, mosfets, caps, etc, including precision resistors.
    • I know how to build a 5V PWM with independent variable frequency and variable duty cycle, and I have all the components I need readily available, but I don't know how to build a decent function generator (yet)
    • I have access to a decent adjustable voltage power supply unit.
    Anyone out there with some experience on this field that could help me solve this riddle?
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Do you have any idea of its original purpose?
    What are the dimensions?
    If you have a low voltage transformer, 6v-12v etc, you can energize one side and read the other and at least get the ratio.
    Max.
     
  3. cmartinez

    Thread Starter AAC Fanatic!

    Jan 17, 2007
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    The transformer is used to actuate a piezoelectric valve on a high pressure pump (my guess is that it works at around 20 Kpsi). Its input waveform is very peculiar. It starts with a series of pulses of up to 120V, then it "coasts" with small pulses of 12V, and then it shuts down with a negative 75V pulse in the end. The whole process takes about 7ms, in repetitive cycles (about 60 hz).
    The attached image shows what I'm talking about. The yellow trace belongs to what I call the positive wire, while the green one to the other wire. No part of the transformer is actually connected to ground... maybe with the possible exception of its core.

    Capture.png
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If it is mild steel laminated core etc, the low voltage transformer idea will tell you the ratio, why do you need the specs if you already have it working in an app?
    More info in the equipment it is hooked up to would be needed for more.
    Max.
     
  5. wayneh

    Expert

    Sep 9, 2010
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    Since you have typed your response into something, you do have a device that can act as a signal generator, at least in the audible range. Any computer or smartphone can run a free app to generate tones with various wave shapes and frequencies. Granted, not enough to drive a 0.75Ω load without amplification.
     
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