Transformer Identification

[MarkB]

I posted a question on here a while ago about identifying a transformer I have... I dug it up - and here's what it is..

fairly hefty - likely an output transformer.. weighs a few pounds.

Markings:
5T-981UL
2003 (this is NOT the year - it came out of a very old receiver)

Wires:
one side has
1 yellow, 1 white, 1 black, 2 blue
other side has
1 black, 2 yellow, 2 red

Hope that's any help -I'd love to know if it's useful for anything
"-)

[hawkeye2u]

Does the transf sit in the power supply or is the secondary winding connect to the loudspeaker.
If it is faulty return it to a guy or company that rewires transformers
usually a LOT cheaper than a replacement tranny from the manuf.
Example I had a 400w bass amp in for repair with the mains tranny COOKED (some idiot over fused the unit)
Replacement value was $295
I had it rewound for $100
We are talking AUS$ here not to confuse U's all

Find out where the tranny is located, prim to sec voltage or an impedace transformer
There is also a chance of locating the circuitry from old vintage sites on the net

[MarkB]

it's sitting here on my desk... I pulled it out of an old quadraphonic receiver.. so I have no idea how it's supposed to hook up.

I was hoping it would be usable for building something like a Firefly.
"-)

[R.G.]

You'll need: AC voltmeter or multimeter with AC-reading scales; source of low voltage AC (half of a 6.3Vct filament transformer output works OK); Ohmmeter; paper; pencil or pen; calculator; scale or comparison known transformers.

0. identify what the transformer likely is; do not use this procedure on tiny transformers, toroids, ferrite transformers, or other things that are not power or output looking devices. Only try this on laminated core transformers similar to the size of a medium wall wart or bigger. BE INCREDIBLY CAREFUL IN THE USE OF AC POWER LINE POWER IN MAKING ALL OF THE TESTS, AND BE HONEST WITH YOURSELF - DO YOU ALREADY *KNOW* HOW TO DO THIS SAFELY? IT'S NOT WORTH DYING FOR - SO DON'T!

1. using the ohmmeter, identify what's connected to what, including if any lead is connected to the core, especially if the core pieces have a weld across them.
2. using pencil/paper, make a drawing of what's connected to what, and what the resistances between the leads is.

3. using the resistances as a guide, guess at what windings are high voltage versus low voltage. High voltage windings tend to have high(er) resistances than low voltage ones.

4. using resistance as a guide, guess at the winding configurations. Centertapped windings tend to have almost but not necessarily ideally balanced resistances on each side of the centertap. Tapped windings having a big resistance and several small ones at one end of the big resistance tend to be tapped primaries (like 110/112/117/120Vac)

5. having identified what's what, apply the source of low voltage AC (3V is good) to one of the moderate to high resistance windings. This is to give you a good chance of keeping the voltage on all windings low. YOU MUST KEEP EVERY SINGLE LEAD FROM SHORTING TO ANOTHER LEAD DURING THIS TEST; YOU POTENTIALLY CAN DESTROY THE TRANSFORMER AND YOUR AC SOURCE IF YOU LET THEM SHORT. Measure the voltages on all windings very accurately. If the voltages are too small to measure, move your 3Vac source to a lower resistance winding and remeasure until you get usable readings.

6. using calculator, compute the voltage ratios between windings, choosing one winding at random or by guess as "1". Make a table of these ratios.

7. now the guessing starts. Pick a high voltage winding, and assume that it has 120Vac on it. Compute the voltages on the other windings. With a full set of voltages, look at what you got. Do any of them make sense? Guessing is going to be required. No? Pick another winding for 120Vac and see if that makes things pop into place.

Power transformers tend to have the lowest winding be 6Vac, perhaps centertapped. Lower than that is highly unlikely. Output transformers tend to have voltage ratios of 12:1 to 30:1 for primary to output ratios.

8. Guess at the power: do this by comparing weight of the unknown against similar transformers that you do know the power rating of.

9. Special considerations: When you think you know what the unknown might be and you are intending to use it for a power transformer, make sure that all windings are unloaded and connect it up to power for a while to see if it gets hot. This is an acid test. Guess wrong, it goes up in smoke. But you want it to go up in smoke under test on your bench, not in your equipment.

10. Do not ever rely on a power transformer you indentify in this way when you are not personally there to make sure that you can put out the fire it starts when it fails if you guessed wrong.

[MarkB]

holy crap, RG...

Thanks for the detailed tutorial!
I'm thinking I may put this tranny on a shelf for a while until I 'get it' a bit more..  
"-)