help with 2x15 transformer

[thebadtall]

Hello. I have bought a 2x15 transformer I thought it was center tapped, but it has two black and two blue cables for secondary.
I connect both black together as ground to an amplifier board and each blue seperate. Then the trafo gets really hot instantly.
Any idea what's going on ? Any different wiring ideas ?

I measured both blacks and got four ohm resistance. If I connect only one black as gnd the amp plays but with heavy distortion as the one rail gets more power than the other .

If I use positive and negative regulators will find some solution ?

Thank you

 

[tgootee]

You can make it just like a center tap, if you connect the correct two secondary wires to each other. i.e. Connect the secondaries in series and then their center connection can be used as a center tap. But you will need to get the phasing correct.

You FIRST need to measure ALL of the resistance combinations, with the wires marked to distinguish between the two blue and the two black.

TAG the secondary wires, with Blue1, Blue2, Black1, Black2.

Then post your measured resistances for (with no transformer wires connected to anything else):

1. Blue1-Black1
2. Blue1-Black2
3. Blue1-Blue2
4. Blue2-Black1
5. Blue2-Black2
6. Black1-Black2

After that, there should only be two possible ways to connect the secondaries in series. And only one of those will have the correct phasing, which should be obvious from measuring the output voltage across the series combination of the two secondaries.

Do you not have a wiring diagram for your transformer? (Post it, if you do!)

Also, post your power supply schematic, of the circuit you actually have.

 

[thebadtall]

Hello and thank you. I will try that as soon as i get back home.
The order of cables is blu blu black black
Maybe the second blu and third black are common

 

[thebadtall]

Hello, here are the measurements. The NO RESTINACE READING means that I've turned the multimeter to 200M ohm range and still got no reading (i got a UNI-T UT50A meter)

BLUE1-BLACK1 NO RESTINACE READING - 0.5VAC
BLUE1-BLACK2 NO RESTINACE READING - 17VAC
BLUE1-BLUE2 3 OHM - 18VAC
BLUE2-BLACK1 NO RESTINACE READING - 16VAC
BLUE2-BLACK2 NO RESTINACE READING - 0.5VAC
BLACK1-BLACK2 1 OHM - 18VAC


any ideas on how to wire it ?
Thank you

 

[tgootee]

OK. Now we know the two secondaries are actually independent. We probably need to know the phasing direction.

Test both ways of connecting them in series:

1. Try connecting blue1 to black1 and measuring voltage between blue2 and black2.

2. Then try connecting blue1 to black2 and measuring voltage between blue2 and black1.

Not sure if any load is needed, to see the difference. I think that one way should give 36V, capable of driving up to transformer rating, and the other way will not work very well, and might even give near zero voltage.

You should probably connect a light bulb in series with the primary, to protect the transformer, during testing.

You could also try both ways of connecting the secondaries in parallel.