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I already have a transformer 2x 6V outputs. I was wondering can I these in series to produce 12V? Similar to how you would wire two 1.5v batteries to produce 3V.

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Yes, transformers with this configuration are designed to be used in this way if required.

  • You can wire the secondary coils in series to get twice the voltage.
  • You can wire the secondary coils in parallel to get twice the current.
  • You can use each secondary independently to get two power supplies.
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  • \$\begingroup\$ Sometimes one output (wire) is in fact common so the last option is out. All the others are still possible though. \$\endgroup\$ – jpc Apr 3 '11 at 18:23
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    \$\begingroup\$ @jpc: Not always, I've used many transformers that have two separate unconnected secondary coils. \$\endgroup\$ – BG100 Apr 3 '11 at 20:28
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    \$\begingroup\$ @BG100 I believe that is what is generally meant by the word "sometimes" which I used. ;) \$\endgroup\$ – jpc Apr 3 '11 at 21:40
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    \$\begingroup\$ when paralleling secondaries you have to be careful to connect them with the correct polarity. Do it wrong and what you effectively have is the two in series and shorted out. \$\endgroup\$ – JustJeff Apr 3 '11 at 22:39
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    \$\begingroup\$ @jpc - The only case I know of with a common wire is when the two coils are in series and the common wire is a center tap (CT). In those cases you can still create two power supplies from it, one positive and one negative. \$\endgroup\$ – stevenvh Apr 4 '11 at 13:14
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If wired in series, you will get double the voltage but the VA will be equivalent to only one of the transformers. If wired in parallel, you will get the same voltage as just using one, but you will double your VA. You MUST use transformers of the same VA and turns ratio.

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  • \$\begingroup\$ The OP is talking about two windings on the same transformer, not two transformers. \$\endgroup\$ – Dave Tweed Nov 2 '12 at 22:33
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The answers to these questions are not as straightforward as the responses suggest. Connecting transformers in parallel can be dangerous if the output voltage of each is not very close to the same. Transformers exist that are made for the purpose. Even a difference of 1V between the two can cause big problems. The voltage difference causes circulating currents that will quickly overheat windings and, either rapidly or over time, break down the insulation between windings and short them out.

Because transformers are often used with currents and voltages that can be hazardous to life, an investigation of the specific considerations applicable to the application is much safer than experimentation.

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    \$\begingroup\$ While all true, the question asks about wiring them in series. \$\endgroup\$ – Ignacio Vazquez-Abrams Feb 18 '14 at 3:20

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