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How do we design a toroidal transformer?


Concerning the mouse and the control buttons

You can use the mouse for everything.

The menu control can also be activated by means of the Alt key and the control letter for the menu option (after pressing the Alt key, it is normally visible in a different color). Some important menu options can be activated by means of the F keys.

Here is a survey of all control keys:

F1 On-line help
F2 It loads your last input file into the input mask in which all of the input data and the results of design are stored
F3 Loads the last input from the user, without any results of the design
F4 Starts design from the input data form
F5 Activates the test mode. This button cannot be pressed until after completion of design
F6 Designs in the test mode
F7 Indicates the loaded or calculated output data
F8 Prints out the loaded or calculated output data
F9 Activates the choice of core family and core with bobbin, and starts manual inputting of core, bobbin and casing
F11 Activates the choice of steel quality
F12 Activates the choice of wire family and wire
Ctrl-F1 Activates help for on-line help
Ctrl-Z Reverses the last input
Ctrl-X Stores all input data from a secondary into the internal memory. The cursor should be located in an input field of the secondary to be copied
Ctrl-C Overwrites the input data of a secondary with the input data from the internal memory in which the cursor is located
Ctrl-V Joins the input data from a secondary with the input data from the internal memory in which the cursor is located. The input data of the 8th secondary will consequently be lost
Ctrl-D Deletes the selected secondary winding
PgDn/PgUp Completes the input for primary voltages or secondary windings. Steps between the Primary, Secondary and Mask input groups
Arrows Steps between the input fields in the input form and in the test mode
TAB Steps between the input fields

Run RALE DESIGN System for toroidal transformers

After installation of the RALE Design System , you see the Rale Design System program group on-screen.

Click on the Toroidal Transformers bottom

After clicking on the Toroidal Transformers bottom, the main menu for the Toroidal Transformers Program will appear on-screen.

This is followed by the input mask on screen with your input data

Input mask

(Numerical Characters =>Inputting), (Arrow, PgUp, PgDn, Mouse =>Move)

Your last input file will be loaded into the input mask. Here, you can create your input or incorporate the input data from an input data file and thus achieve drastic acceleration in the procedure for filling-in of the input mask.

(TAB=>Steps), (Click=>Marks), (Double click=>Selects)

In the installation of the Rale Design System, a RALE library of input data files has also been installed, with the distinction between two groups:
The first group helps in the design of transformers which are designed in accordance with regulation IEC 61558 (VDE 0551), paragraphs 15.3.2 and 15.3.3.

Example: R1532A4.TR1 or R1533E.TR1

R RALE by made
1532 IEC 61558 Paragraph 15.3.2
1533 IEC 61558 Paragraph 15.3.*
A Insulation class A
E Insulation class E
B Insulation class B
F Insulation class F
H Insulation class H
4 Current rating of fuse < 4A
10 4> Current rating of fuse < 10A
25 10A > Current rating of fuse < 25A
63 25A > Current rating of fuse < 63A
99 63A > Current rating of fuse < 100A

For all input data files, an ambient temperature of 40oC has been used.
After loading of an input data file from this group, you now only have to enter the value for voltages and currents in the input mask.
The second group of input data files illustrates how it is possible to design certain specific transformers. All of these input data files are extensively discussed in the design examples.
The third group of input data files should be created by yourself in the course of time.


The input mask consists of 5 areas:

  1. Menu bar.

  2. Input form for primary data.

  3. Input form for secondary data.

  4. Input form for general technological parameters.

  5. Status line


The 6 fields of the status line indicate, in sequence, the core family, the core, the iron quality family, iron quality, and the minimum and maximum values of the current input.
The input process for primary voltages and the secondary windings is concluded by means of the PgUp or PgDn keys

On-line Help

Key F1 plays an important part at this point, because each input field has a help text. Use ESC to quit on-line help.

(Mouse, PgDn, PgUp, Arrow =>Move), (ESC=>Exit)

The input fields which are marked * are values with a unit of quantity (V, A, Hz,...) or multiplication factors. The input fields with - are code values. These can be entered or selected via the Options menu.


Wires and steel

The input fields for Wire type (not wire size) and Steel are a minor exception in this instance and can be selected in addition to manual input via the Material/Wires/Fe menu or selected by means of keys F11and F12.

(Alt-M and F or F11only =>Fe-Quality), (Alt-M and W or F12 only =>Wires)

(TAB=>Move), (Click=>Mark), (Double click=>Select)

(TAB=>Move), (Click=>Mark), (Double click=>Select)

Core and bobbin unit

Using the menu option of Material/Cores or key F9, you can select a core with a given bobbin or set up your own preferred combination.
The distinction is drawn between 4 different approaches for selection of the core and of the bobbin:

Automatic selection
(Selection = 0)

In this mode, you just know the core family for the core and the coil from which you have to choose. But you don’t know which core is suitable for your application.

  • Enter a 0 in the Selection input field.
  • The core name in the status line must be AUTO.

Core and bobbin are selected
(Selection = 1)

You wish to produce your application with a given core and a given bobbin from a given core family.

(Alt-M and C or just F9 =>Cores and Bobbins)

(TAB=>Move), (Click=>Mar), (Double click=>Select)

  • Select the Material/Cores menu option or press key F9.
  • Select a core family.
  • Use the mouse to click on the core you prefer.
  • Click on the OK button. The Selection input field has automatically acquired the value of 1.

Core and bobbin are incorporated from a single input data file
(Selection = 2)

We have already selected an input data file before accessing the input mask, or we have loaded an input data file from the input mask via the Input/Open menu option. In this instance, we incorporated the core and coil stored in this input data file. The input field for Selection has a value of 2. Using this procedure, we have no further work to do with regard to core selection on-line.



(TAB=>Move), (Click=>Mark), (Double click=>Select)

The core and bobbin are manually entered
(Selection = 3)

You wish to achieve your application with a given core and a given bobbin, but the core does not exist in any core family.

(Numerical =>Input), (TAB, Mouse =>Move)

Note 1 : If you change the core sizes Di, Da and H the program will show you the maximal, optimal sizes of the transformer Diw, Daw and Hw.

Note 2 : If you change the sizes of the transformer Diw, Daw and Hw the program will show you the minimal, optimal sizes of the core Di, Da and H.

(Numerical=>Input), (TAB, Mouse=>Move)

  • Select the Material/Cores menu option or press key F9.
  • Select a core family which could include your core.
  • Use the mouse to click on a core which is similar to yours.
  • Use the mouse to click on the Copy button and then Yes.
  • Change the core, the bobbin and/or the case.
  • Click on the OK button. The Selection input field has automatically acquired the value of 3.

Under this procedure, we have no further work to do on-line with regard to core selection.

Saving the input data file

Your input is COMPLETE! It is recommended that you save your input data into an input file.

(Alt-I and S)

(TAB => Move), (Click => Mark), (Double click => Select)

  • Select the Input/Save menu option
  • Enter the name of your input data file (max.of 8 characters, and the extension .TK1 cannot be modified).
  • Click on the OK button.

Run designing

Design is started via the Run/Start menu option or with key F4.

(Alt-R and S or just F4)

If you have not already selected a core, the program starts automatic search in accordance with one of your requirements from the core size as per your inputting, from the selected core data file.

The program starts searching at the first core of the core family and passes through to the last core in the family in sequence. You are invited to approve the first core which is adequately large for your application.

This is followed by the design operation. Note that there are 2 criteria of the optimizing: dT => temperature rise or dU => Regulation

Data page for winding
After the design procedure, a summary of the main results will appear on-screen.

(Mouse, control bar, Arrows, PgUp, PgDn=>Move)

The continuation of the above screen illustrates the extensive display of the design results. Each designed value is allocated with an appropriate explanatory text.

If you should need further information, please locate the cursor on the size value and press key F1. This activates on-line help.

(Mouse, PgDn, PgUp, Arrows=>Move), (ESC=>Exit)

Press Key "1"..."9"  to jump to the other screens or press F8 to print the calculated results :


If you are not satisfied with the results of design, you can :

  • Return to the input form via the Input/Current menu option or by means of key F2, and reconfigure the input data on-line
  • Or pass to the test mode via the Input/Test menu option or with key F5.

Activate the Input/Test menu option or press key F5.

Test mode

(Alt-I and T or F5 only)

In the test mode you can test a designed transformer and manually change its parameters.

(Numerical =>Input), (TAB, Arrows, PgUp, PgDn, Mouse=>Moved)

The input fields with the white background can be modified. For instance, if you want to change the wire size you have to move the cursor to the wire number:

Click the menu option Material/Wires or press F12 to open the list with the wires.


This is he current wire size

Select the wire size which you want and pres Alt-O or click OK

Re-design in the test mode is activated via the Run/Test menu option or by means of key F6.

(Alt-R and T or F6 only)


Help in test mode

In order to get on-line help in the test mode place the cursor where you need help and press F1



The printing is performed via the Output/Print menu option or by means of key F8. After activation of the print process, the data, totalling approx 16kB (3 pages), is printed on your printer. You can too save the results of design on your PC and load them and print out later. The procedure for saving of the designed data looks like this:

Saving of results of design

Saving of the designed data which you can load and print out later on the data page for the winding, is activated via the Output/Save menu option.

(Alt-A and S)Enter a name for the output file in which the designed data is to be saved.

(TAB=>Move), (Click=>Mark), (Double click=>Select)

This completes your design.

Quitting your RALE Design System for toroidal transformers

Select the Input/exit menu option or press key Crtl-F12 and then click on the Yes button.

Important note:

In this context, we have just discussed the procedure for design of the toroidal transformer. There is extensive coverage of the technical aspect of design, within the design examples.