Mystery Transformers Okay
I figured the wirings of my Mystery Transformers all wrong.
Mystery Transformer “A”
Previously I suspected either high inrush current or shorted primary windings. So I measured Mystery Transformer “A” using my GM328A component tester, and posted my findings and suspicion to EEVBlog forum.
A regular poster swiftly confirmed that it was shorted, but then three other regulars suspected that the yellow wires were actually for the secondary winding.
As you can see in post #9 in that topic, that made me retest Mystery Transformer “A”, switching my assumption about the wires.
- Black-Blue-Red now assumed as primary (0-110-220VAC).
- Yellow-Yellow now assumed as secondary.
I performed two 5-minutes test, connecting Black-Red to mains, with no-load on the secondary:
| № | Measurement | 1st Test | 2nd Test |
|---|---|---|---|
| 1 | Mains/Primary Voltage | 218VAC | 218VAC |
| 2 | Primary Current (Min) | 26.34mA | 25.97mA |
| 3 | Primary Current (Max) | 28.15mA | 28.21mA |
| 4 | Secondary Voltage (Min) | 10.14VAC | 10.07VAC |
| 5 | Secondary Voltage (Max) | 10.33VAC | 10.32VAC |
| 6 | Smell | None | None |
| 7 | Temperature | Cold | Skin warm |
Smell wasn’t an actual measurement. I just whiffed the transformer after disconnecting it from mains. If it smelled like burning insulation, we knew something was wrong. As for temperature, I could not measure actual temperature with the multimeter’s temperature probes, because the multimeters were already being used in this test.
Everything were fine: breaker didn’t tripped, transformer didn’t smell and didn’t heat up, and the secondary (Yellow-Yellow) were giving out sensible no-load AC Voltage. Yellow-Yellow really were the secondary, and windings weren’t being shorted.
So I replicated the assumption for Mystery Transformer “B”.
Mystery Transformer “B”
- White-Blue-Red now assumed as primary (0-110-220VAC).
- Yellow-Yellow now assumed as secondary.
White-Red to mains, no-load on secondary. Result:
| № | Measurement | 1st Test | 2nd Test |
|---|---|---|---|
| 1 | Mains/Primary Voltage | 218VAC | 218VAC |
| 2 | Primary Current (Min) | 39.93mA | 39.63mA |
| 3 | Primary Current (Max) | 41.30mA | 41.13mA |
| 4 | Secondary Voltage (Min) | 15.18VAC | 15.47VAC |
| 5 | Secondary Voltage (Max) | 15.13VAC | 15.44VAC |
| 6 | Smell | None | None |
| 7 | Temperature | Cold | Skin warm |
Everyhing were also fine with this transformer. Just like Mystery Transformer “A”, for “B” Yellow-Yellow were secondary, and nothing was being shorted.
Conclusion
Both transformers are fine. The Yellow-Yellow wires on both transformers are actually for the secondary windings.