How to tell if this transformer is faulty?

[reddish75]

This transformer in and out of circuit lights up my dim bulb tester brightly and doesn't dim, how do I test the transformer to see whether its faulty? Here's some resistance and continuity measurements as I couldn't think of which other tests to do,

Secondary resistance measurement

Across k25 0.64r continuity across

Across k23 3.45r continuity across

Across k22 0.52r continuity across

Across k24 pins 1-3 4.78r continuity
                       3-2 2.49r continuity
                       1-2 2.49r continuity

Primary resistance measurement

Across k21 pins AC 3-5 9.68r continuity
                            5-4 2.25r continuity
                            4-3 7.62r continuity

[armandine2]

check for shorts - I wonder why the primary resistances are so different?

[eblc1388]

Primary resistance measurement
Across k21 pins AC 3-5 9.68r continuity
                            5-4 2.25r continuity
                            4-3 7.62r continuity

These two 115V windings should have roughly the same ohmic values because they both have the same number of turns. However, because one is wound on top of the other I would expect ohmic difference of 10%~30% max. between the two.

In your case, such large ohmic difference indicates a possible inter winding short circuit. Try back feeding the transformer using a few volts AC from the secondary side and measure any possible voltages on the primary.

Another test you can try while using the dim bulb tester is to short circuit any pair of the the secondary windings. If the light doesn't shows brightness changes, then the transformer is definitely faulty.

[srb1954]

This transformer in and out of circuit lights up my dim bulb tester brightly and doesn't dim, how do I test the transformer to see whether its faulty? Here's some resistance and continuity measurements as I couldn't think of which other tests to do,

Secondary resistance measurement

Across k25 0.64r continuity across

Across k23 3.45r continuity across

Across k22 0.52r continuity across

Across k24 pins 1-3 4.78r continuity
                       3-2 2.49r continuity
                       1-2 2.49r continuity

Primary resistance measurement

Across k21 pins AC 3-5 9.68r continuity
                            5-4 2.25r continuity
                            4-3 7.62r continuity

Do you have an LCR meter?

Checking the inductance of windings is useful if you suspect that there is an internal shorted turn and often gives a better indication of a problem than resistance measurements.

For a normal transformer the inductance ratios between the various windings should be approximately the square of the voltage ratios between the respective windings. Any significant deviation from these ratios indicates a possible shorted turn.

[dietert1]

As the primary is one coil it does not have two parts of 115 V each that can be used in parallel for 115V operation. So it has one strong 115V partition with lower ohms and the whole primary for 220V with somewhat higher ohms. Thats OK.

Regards, Dieter