Posted by Wayne Parham [ 66.137.59.97 ] on May 22, 2004 at 04:37:02:
In Reply to: Tranformer testing??? posted by jim denton on May 21, 2004 at 08:45:23:
You can test to see if any of the windings has opened up with an ohmmeter. The connectors to the primary winding(s) should show continuity and the connectors to the secondary windings should also show continuity, but the meter should show open between the primary and secondary. This won't tell you if windings have shorted, but it will tell you if they've opened up.
The most likely failure mode of a power supply transformer is for it to open, so if there's continuity, I'd feel pretty comfortable powering it up. A technician might use a variac to apply power slowly, measuring the voltage output on the secondaries after verifying that the windings weren't open. A drastically low voltage condition indicates that windings are open. With the input power at say 1/4 line voltage, you'd expect the secondaries to all be at 1/4th their voltage rating and if that weren't the case, the transformer might be shorted. But like I say, the most common failure mode is open windings.