Is there a way to identify the phase of the transformer's coils without having to see its waveform in an oscilloscope?

For example, I have this unknown switching transformer enter image description here enter image description here

The only thing I know is the continuity between its pins, this is by measuring continuity with a Digital Multimeter enter image description here

and the inductance between each pin by measuring it with a transistor tester

1,4,5 Pins

  • 1-4 = 0.24 mH / 1.0 Ohms
  • 1-5 = 0.8 mH / 1.8 Ohms
  • 4-5 = 0.17 mH / 1.1 Ohms

2,3 Pins

  • 2-3 = 1.24 uH / 0.5 Ohms

6,7,8,9 Pins

  • 6-7 = ... / 0.4 Ohms
  • 6-8 = 1.24 uH / 0.4 Ohms
  • 6-9 = 1.24 uH / 0.4 Ohms
  • 7-8 = ... / 0.4 Ohms
  • 7-9 = 1.24 uH / 0.4 Ohms
  • 8-9 = ... / 0.4 Ohms

How do I know what is the direction of the windings? How do I know what would be its equivalent circuit representation?

  • \$\begingroup\$ What does it mean that your 6-7, 7-8, and 8-9 readings are all "..."? Did you forget to measure those? \$\endgroup\$ – Hearth Oct 13 '19 at 14:44
  • \$\begingroup\$ it means that my transistor tester does not show a value for those .. maybe the inductance is too small, so it is out of the range of the Transistor Tester, but I don't know .. I am glad you ask \$\endgroup\$ – DieDauphin Oct 13 '19 at 15:38
  • \$\begingroup\$ Do you have a multimeter? I suggest measuring the resistances of each pair of pins; it'll give a rough idea of what's in there even for the ones out of range of your "transistor tester" (which is apparently also an LCR meter) \$\endgroup\$ – Hearth Oct 13 '19 at 15:50
  • \$\begingroup\$ Yes, it is also known as component tester .. but it is weird, because, the range it has is supposed to be: 0.01 mH -20H \$\endgroup\$ – DieDauphin Oct 13 '19 at 15:53
  • \$\begingroup\$ You really can't trust the specs on cheap stuff you get on ebay or aliexpress, really (and I'm assuming you did get it from one of those sources, as component testers are much more of a hobbyist thing than a professional thing) \$\endgroup\$ – Hearth Oct 13 '19 at 15:55

Your first image is out of focus, but it doesn't appear to have any markings on it that might help. Failing that, you may be able to tell which pins are the start and which the ends of the windings as follows, provided you have a suitable signal source of some kind.

Let us ignore the taps in the windings for now and call them 1-5, 2-3 and 6-9.

Pick any winding, say 1-5, and apply a signal to it, say 1V RMS at 1kHz (you need to pick the amplitude and frequency to give reasonable results with your meter whilst not driving the transformer too hard)

Measure and take note of the RMS voltage across 2-3 and 6-9 separately.

Now connect, say, 3 to 6 and measure again between 2 and 9.

If this voltage is the sum of the first two readings then the windings are in phase and you can say 2 and 6 are the starts and 3 and 9 the ends. If the voltage is the difference the the opposite is true. Confirm this by connecting, say, 3 to 9 and measuring between 2 and 6 when you should get the sum.

Note the sum of the voltages may not be quite the same as the combined reading, but if the windings are in anti-phase then it should be considerably less. Also this gives you the relative phase of the two windings not the absolute start and finish of the original winging process.

You can now repeat the test with a different pair of windings, say drive 2-3 and measure 1-5 and 6-9, to get their relative phase. You now have the relative phase of all windings and you can double check by using the last possible combination (drive 6-9, measure 1-5 and 2-3). The ratio of voltages will also give you the turns ratios of the windings.

It is probably safe to say that the taps are in sequence on 6-9, but you can use a similar test to confirm this if there is any doubt.

Note that you appear (from the ratios of the inductances) to be working with a transformer with a fairly high turns ratio, driving the LV side can result in unpleasantly high voltages appearing across the HV side, so take care.

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The polarity relationship between the windings is simple to determine with a DC kick test. The figure shown at this link is the circuit you need. You just apply a very short pulse. Best if you have an analog volt meter.

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  • \$\begingroup\$ I wouldn't do this without a resistor in parallel to the voltmeter, lest you damage the meter by overvoltage. \$\endgroup\$ – Hearth Oct 13 '19 at 14:43

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