DIY Tutorial - Wiring a Toroidal Transformer

Wiring a toroidal transformer with a single primary winding to 2 isolated secondaries

This is the simplest way to connect a toroid with 2 secondary windings. This is valid for modules that accept the voltage of the toroidal transformers in question and have AC-0 / AC-0 connectors. However, with a toroidal transformers having several secondary windings, it's also possible to create a mid-point, to connect them in parallel or in series.

Wiring a toroidal transformer with a single primary winding to 2 secondaries by creating a midpoint

In this case, we have a single primary (P) receiving a mains voltage of 230V and two secondary windings (S1 and S2) that we can wire by creating a midpoint. For example, for a 2x(0-15V) toroid, the two secondary windings each deliver voltages of 15V AC per winding. To create a reference point, simply connect one of the two cables of each secondary winding whose voltages are in phase opposition. This will create the “artificial 0”.

Wiring a toroidal transformer with a single primary winding to 2 secondaries connected in parallel

The two secondary windings can also be connected in parallel, to maintain the voltage of a single winding while doubling the current capacity.

Wiring a toroidal transformer with a single primary winding to 2 secondaries connected in series

Series wiring allows the voltages of two windings to be added together, while maintaining current capacity.Series wiring allows the voltages of two windings to be added together, while maintaining current capacity.

Example of a 2x15V + 1x9V toroidal transformer

This toroidal transformer has 3 secondary windings, including two 0-24V AC and one 0-9V AC. You can therefore make all the connections described above with the two windings of the same voltage, but also supply an additional module or part of a module with 9V AC.

Example of a 15-0-15V + 1x9V toroidal transformer

This toroidal transformer has 2 secondary windings, one 15-0-15V AC and one 0-9V AC. You can therefore supply one module with an AC-0-AC input and another with a 0-AC input.

Connect two 115V AC primary windings to 230V AC.

Simply wire in series.

Connect 2 primary windings 115V AC to 115V AC

Simply wire in parallel.

Example of a shielded toroidal transformer

This type of custom-built toroidal transformer features a green/yellow cable connected to earth, enabling the installation of a shielding screen. This cable is not connected to the transformer coil, but to a metal plate. It is usually grounded via the device housing, for example. There are two types of shielding:

- Electromagnetic shielding: protects external components from any electromagnetic waves emitted by the transformer.
- Electrostatic shielding: protects the transformer's internal coil from the electrostatic waves it emits.

Example of a toroidal transformer with thermal fuse

This type of toroidal transformer is made to custom specifications. Either the manufacturer directly wires the fuse internally in the transformer, or he leaves the cables visible, allowing the thermal fuse to be used. In this case, it's up to the user to wire the fuse correctly. To wire your thermally fused toroidal transformer properly, simply make a series connection, ensuring that the fuse is on the phase side to avoid any persistent current.  

The winding identification convention

There is a phasing convention for toroidal transformers, represented by a dot on the diagrams. This is used to phase the primary and secondary windings. At Audiophonics, toroidal transformers are designed so that the windings start counter-clockwise. Below you'll find the correspondence between the electrical diagram and the physical representation of a toroidal transformer. Use the indications on the toroidal transformer as a guide.