Transformer wiring question, series, parallel and center tapped

[swin1]

Hi there, long time reader, infrequent poster.

OK probably an awkward and silly question, but I am trying to learn more about options for wiring a transformer.

Now, I am comfortable with wiring transformers in series/parallel and know the general rules.

But, I am curious, I have a transformer with 2 different outputs - 16v-0-16v, and 38v-0-38v. Obviously it's useful for a high power integrated amp, but is there a way of providing 22v-0-22v by series wiring and out of phase (subtracting voltages,) or does the fact it's centre-tapped prevent any alternative wiring options.

Your input would be greatly appreciated, and perhaps could lead to a discussion that would help everyone have a better understanding of transformer wiring in general.

Cheers

 

[winny]

Unless I have missed something, no.

You can get 2*22 V, but not 22-0-22.

 

[swin1]

Thanks, could you explain more about wiring multiple centre-tapped transformers together, in series or parallel, so that if I were to use more than one transformer in a system I might understand my step down options. I would really appreciate it.

I'll provide a picture of what I'm trying to get at if needed.

Thanks

 

[winny]

Something like this.

Remember that this is not a good solution as the transformer utilization will be low. Can you rewind the 38 V transformer, or add windings to the 16 V one?

 

[Eva]

Something like this.

Remember that this is not a good solution as the transformer utilization will be low. Can you rewind the 38 V transformer, or add windings to the 16 V one?

It won't work that way, there is no way to join the voltages obtained.

 

[winny]

Eva,

Exactly! That's why I wrote 2*22 V but no 22-0-22.

 

[AndrewT]

open up the outer insulation and separate the windings at the centre tap to create a 0-16-38+0-16-38Vac transformer. But while you can see the windings check/measure the wire diameters. They may be different in the two parts of the winding.

 

[winny]

AndrewT,

Yes indeed!

 

[swin1]

hmmm... centre of transformer is filled with polyurethane with a nut in the middle for mounting, essentially blocking the inner core so I can't exactly unwrap the plastic, or if I could it would take forever to wrap up again. the secondaries are exactly opposite each other on the transformer, so I'm assuming it would take some unwinding to bring them together. I think this time I will leave this one alone and use it for something else or sell it.

So based on this discussion I'm assuming in general if centre-tapped transformers are to be used in multiples, in series, winding them back to find the ground reference and splitting that will give V-0 V-0 (whatever V is)?

Thanks a lot for your inputs!

 

[AndrewT]

centre of transformer is filled with polyurethane ............................ the secondaries are exactly opposite each other on the transformer, so I'm assuming it would take some unwinding to bring them together.

drill a ring of small holes through the core filling. It will probably push out or take a little more effort.
Where is the centre tap lead? That's the one you need to access.

 

[WinCrazy]

Dealing with AC, *not* DC

Swin1, Because the xformer has 3 wires, you can get ONLY two 16 volt outputs (which may be tied into parallel to provide up to double the possible current or a SINGLE 32 volt out put. You CAN NOT get any 22 volt output !! Also know that the output voltage are *very* approximate. You need to know whether the stated voltages are peak voltages or power-average voltages (RMS).

 

[AndrewT]

ignore post 11.
you cannot parallel a centre tapped to obtain double the current.
You can get a 22Vac output, but it is limited to the current available from the 38Vac tapping. But, it is not isolated from any other output voltage, this restricts what you are able to do with the other tappings.

 

[megajocke]

How do we know the 16-0-16V winding is not a low current one?

Doing what AndrewT suggest, unwrapping the plastic and separating the centertap is best. You can also check wire diameters then to calculate how much current you can draw from the different windings. A milliohmmeter is another possibility.