[solved] Transformer wiring question

[RayRay]

Hey guys. I'm trying to replace an R-Core transformer with a Toroidal on an audio circuit, and I'm a bit confused on the 0v wiring. The original transformer has dual 15V secondaries with a single 0V wire for both, however, the new one has two 0v wires (one for each secondary) so I'm a bit puzzled. Should I use only one of the 0v wires, or combine em? Thanks.

[iMo]

With 2 secondaries you have to wire them as follows:

1.    start------- ~15V
2.    end---
               |----- "0"
3.    start--
4.    end--------- ~15V

PS: let us call "end" your two "0V" wires..

[bdunham7]

Hey guys. I'm trying to replace an R-Core transformer with a Toroidal on an audio circuit, and I'm a bit confused on the 0v wiring. The original transformer has dual 15V secondaries with a single 0V wire for both, however, the new one has two 0v wires (one for each secondary) so I'm a bit puzzled. Should I use only one of the 0v wires, or combine em? Thanks.

There is no 0V wire on an AC transformer winding, you'll need to think about it just a bit more or you're going to get something out of phase, the results of which could be a short circuit or a just a non-working circuit.

Presumably your old transformer was wired as a single 30V center-tapped winding, or possibly two 15V windings with the appropriate ends connected inside so as to amount the same thing.  To replicate this using a transformer that has two separate windings, you have to connect the correct two wires together to be your center-tap or '0V' wire.  That is all presuming the transformers are configured as I imagine them, which is the most common way.  However, given your description, I can't be completely sure how either of your transformers is actually wired and I don't want there to be any misunderstanding and smoke, so can you post photos of each? 

[RayRay]

I appreciate all the help guys, although, I don't think I've gotten a direct answer to my question.
Anyways, I'll try to explain it again, on the PCB, there are 3 solder joints for the transformer (voltage-0v-voltage). Both transformers (old & new) are dual 15v secondaries rated for 1A each. The original 15v-0-15v, while the new is more 15v-0-15v-0 , so on the new, I have two 0v wires (one for each secondary) and since I only have room for one on the PCB, the question is whether I should use only a single 0v wire, or combine both into it (I just wanna be 100% sure it wouldn't damage the transformer if I'll combine em together)

[iMo]

..while the new is more 15v-0-15v-0 ..

That is exactly what I described to you above in my post.

N1  N2 N3 N4
15v-0-15v-0

Wire together N2+N3 and you will get your "0" wire..

As bdunham7 explained to you the "3 wire" transformer is most probably a standard center tapped transformer.
You should not wire both "0" wires of your "4 wire transformer" together as the remaining 2 wires will then work in phase.

[RayRay]

Pictures of both transformers attached. Again, both are dual 15v secondaries (the circuit itself requires it).  The original transformer has a single, shared 0V wire, and the new (Toroidal) has separate 0v wires for each secondary. Hopefully this would help me get a clearer answer.

[iMo]

With multiple winding transformers it is important to take the "start" and "end" of the specific winding into account..
In the schematics you will sometimes see a "dot" near the "start" of the winding.
See below the link with details:
https://www.electronics-tutorials.ws/transformer/multiple-winding-transformers.html

The principal of operation of a multiple winding transformer is no different from that of an ordinary transformer. Primary and secondary voltages, currents and turns ratios are all calculated the same, the difference this time is that we need to pay special attention to the voltage polarities of each coil winding, the dot convention marking the positive (or negative) polarity of the winding, when we connect them together.

Thus you have to tell us which color is the "dot" side of each secondary winding..
Or which colors are the "15V" wires in your notation.
Or which colors are the "0" wires in your notation.

[RayRay]

Here's the PDF of the toroidal if it helps:
https://docs.rs-online.com/6524/0900766b815bd16e.pdf

[bdunham7]

while the new is more 15v-0-15v-0 , so on the new, I have two 0v wires (one for each secondary)

That makes no sense electrically even if that is what is written on there.  You will need to connect two of the wires and put them into the CT (0V) point on the PCB, but which two wires is the question.  imo's guess is probably correct, but there's not much point in avoiding a very easy test to see which way they should go.  If you can't post photos for some reason, do this:

Check with an ohmmeter to make sure that you have identified the windings and that they are separate.  So between what you are calling 15V and 0V wires, there should be a low DCR from one to the other on each winding, but no continuity between either point of either winding.

Next, verify phase.  Connect 1 of the 15V windings to the 0V wire of the other winding.  Don't mess that up!  Now measure the voltage between the two open windings with an AC voltmeter.  If you get thirty-ish volts you have the correct connection, if you get zero-ish volts, you have the phase reversed.  Once you get it correct, the two connected wires go to the 0V/CT point on the PCB and the other two go to the outer "15V" positions and which one goes where doesn't matter.

Edit: looking at the datasheet you posted, start by connecting the black/yellow wires together and then checking for the 30-ish volts across the red/orange pair.  That will most likely be your final answer!

[iMo]

Here you are:

[bdunham7]

But do test it before you solder it all up!

[IanB]

But do test it before you solder it all up!

The way you test it is to join black and yellow together and then measure the voltage between red and orange. If it is ~30 V then you are good to go. If it is ~0 V then you should join black and orange together. But the PDF clearly indicates that joining black and yellow is the right way.

[RayRay]

Thanks again for the help guys! Will do some measurements later and hopefully figure it out. That said, I think you may have gotten confused on the coloring. First secondary is Red/Black (Red 15v, Black 0v), second one is Yellow/Orange (Yellow 15v, Orange 0v)

[bdunham7]

That said, I think you may have gotten confused on the coloring. First secondary is Red/Black (Red 15v, Black 0v), second one is Yellow/Orange (Yellow 15v, Orange 0v)

No, we got that part right.  If the datasheet is conventionally correct, you will connect the black and yellow.  If the windings are 'in phase', then connecting the two 0V wires will not give you what you want and your circuit will not work.

[IanB]

Thanks again for the help guys! Will do some measurements later and hopefully figure it out. That said, I think you may have gotten confused on the coloring. First secondary is Red/Black (Red 15v, Black 0v), second one is Yellow/Orange (Yellow 15v, Orange 0v)

No, we have not got confused. The PDF makes it very clear that Black and Yellow should be combined to make the center tap.

You want to put the two windings in series to make 30 V total. If you were to put two batteries in series, would it work if you connected plus to plus, or minus to minus? When you put batteries in series, you alternate, plus to minus. Similarly, when you put transformer windings in series, you alternate, connecting like to opposite, not like to like.

[RayRay]

Oh, I see. That makes sense. I just don't fiddle with transformer wiring very often, so wasn't sure how to go about it.
Anyhow, I'll come back with an update a bit later.

[RayRay]

Update: I've done as you've said (combined the black & yellow) and it worked as expected!
The volts coming from the red & orange respectively was a bit higher than 15v though (around 17.70) but according to the PDF, this seems to be normal when there's no load. Thanks again for all of your amazing help guys!