# How do I find the inputs/outputs of an unlabeled transformer?

I’ve been trying to wire a transformer according to this schematic. but nothing is labeled on the actual transformer. There only only colored wires.

On the primary side, the Blue and White wire show a resistance of zero ohms when probed.

On the secondary side, both Red wires along with the Black wire show a resistance of zero ohms while probed, while the Orange and Gray wire show a resistance of zero ohms when probed.

The Green striped wire on the primary side doesn’t seem to be connected to anything when probed. Theres no resistance or anything happening.

To measure the resistance I’m using a digital multimeter first set at 200 ohms, which I recieved a resistance of 0. I changed to the diode continuity setting and still recieved a reading of 0 ohms, which my multimeter also beeped.

The only information I saw on the cover was just this:

 100V
31.9V 102V

FUSE 2A


And yes, the cover actually does say 102V. Could this be a typo? How do I wire this without breaking it?

• how are you measuring the winding resistance? .... include all information ..... add the information to your question ........... do not use comments Oct 31, 2018 at 23:19
• Do you know the function of the device you give the schematic ? This could help answer your question about the 102V Oct 31, 2018 at 23:26
• The function is overall to convert the transformer outputs to 5VDC and 15VDC for use in later applications Nov 1, 2018 at 0:19

The yellow-green wire is certainly connected to the core the transformer, and is to be connected to the ground.

The blue and white seem to be the primary. I am surprised the resistance is exactly 0 ?

If you are sure the transformer corresponds to the one in the schematics, clearly the two red wires and the black one are connected in the same winding, and correspond to pins 6, 7, 8. I guess the two reds are 7 and 8 (order does not matter) and the black one is N° 6.

Of course, orange and gray correspond to 9 and 10 (order does not matter).

Are you sure the primary corresponds to the blue and white wires ? If you are, I think you can plug these two to a 100V AC source (don't forget the fuse). Then, with a voltmeter, you could check that the voltage between the 2 red wires is twice the voltage between one red and the black. If this is correct, my assumption about red/black wires is correct.

If you use a sensitive enough ohmmeter, you should get a small, but not null resistance between the different wires. I think the highest resistance should be between 9 and 10, then a little lower between 12 an 14 (primary). Resistance between 7 and 8 should be lower, and resistances between 6-7 and 6-8 should be half the resistance between 7 and 8.

• Well there are only three wires on the primary side, and from the schematic it’s just a long coil around the magnet, considering how the blue and white wire have zero resistance i thought that would make sense. But it is likely my meter is not sensetive enough. Oct 31, 2018 at 23:50