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I’m currently learning about transformers. I have a quick question regarding the specification of a 2x24/2A transformer.

Here is a picture of the transformer:

Transformer

Does 2x24V mean that this transformer has dual secondary windings that creates 2x 12V 1A output or does it have two 2x 24V 2A or maybe 2x24V 1A? I’m quite confused about how the secondary output works on this transformer.

Crude information about the transformer:

  • Transformator 2x15VAC 72VA
  • Primary: 220VAC
  • Secondary: 2x15VAC 2.5A = 75VA
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schematic

simulate this circuit – Schematic created using CircuitLab

Figure 1. Various wiring options for your transformer.

The secondary arrangement allows various configurations of the transformer output, making it more versatile at very little extra manufacturing cost.

  • Fig. 1a: Independent 24 V outputs, each rated at 2 A.
  • Fig. 1b: 48 V, 2 A secondary with a centre-tap.
  • Fig. 1c: 24 - 0 - 24 V, 2 A secondary. This is the same as 1b except that we have chosen a different point to call 0 V.
  • Fig. 1d: Parallel connection of the coils results in a 24 V, 4 A output.
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  • \$\begingroup\$ Just a minor contribution. Transformers that are 24-0-24 from factory are also specified as 24+24, whereas 2x24 means that they are separate secondary windings. \$\endgroup\$ – Undertalk Oct 18 '18 at 21:25
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Based on the markings on the transformer and the terminals, I would say it has 2 isolated windings. Each winding is rated for 24 volts at 2 amperes. If there were only 3 terminals then it would probably be a center tapped transformer. Since there are 4 terminals, it probably has 2 separate windings. You can make resistance measurements with a meter to determine if the windings are indeed isolated. You can then make voltage measurements to verify the voltage ratings (note that with no load the voltages on each winding may be somewhat higher than 24 volts). It is difficult to verify the current ratings.

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Ok so usually when you have a rating on the transfomer like 2x24V/2A, it means that your transformer has 2 24V outputs and that it is capable of driving a load up to 2A. This means that the total current on all the outputs will be below 2A.

Another case could also be that you have separate windings, so each output can drive at maximum 1 A.

If the input is 220 VAC (Volts alternated current) you have a 325VAC peak-to-peak voltage. The output will be, in this case, 24VAC or roughly 34VAC peak-to-peak. There are 5 pins since one is for reference (0 V).

Regarding the VA (Volt-Ampere), this is transformer's capacity. It has a meaning similar to the Watt power.

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  • \$\begingroup\$ There are only four terminals (pins) on the secondary. There is no 0 V reference. That's up to the user. \$\endgroup\$ – Transistor Oct 18 '18 at 21:18

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