Fill in your specification on the lefthand side. You can also load some common core and geometry properties instead of typing them.
You can specify up to ten windings, with current defined as RMS current entering the winding. You need to select a current or number of turns to be modified automatically to ensure your currents balance. You also specify limits on the core magenetisation.
The transformer design process is as follows: —
 Fill in the specification, including k_{Cu} as the maximum packing factor. Don't forget to press Design now.
 Identify the lowest power that fulfils your magnetisation limit. You may need to choose another core to obtain reasonable values.
 Look up the recommended wire diameters for your k_{Cu}. Enter wire diameters you have available (similar values to the recommendations) and enter them in the specification. Press Design Now again to update the design.
 Choose a number of primary turns with low losses and that is below your packing factor and magnetisation limits.
 Look up the number of turns for each winding.
Processing messages (if any)
Winding recommendations
Below are the best winding diameters and turns (lowest power while obeying magnetisation and k_{Cu} limits). All wire diameters are those listed as available in the specification.
N  D  V  

P_{total}  W  
k_{Cu}  
minimum N_{1}  (magnetisation)  
(saturation)  
model: 

The number of turns is the minimum in the valid region (as shown on the graphs). The wire diameters are initially estimated using uniform current density in the winding area. Between three and seven (depending on number of windings) wire sizes for each winding are simulated and the lowest is power below the k_{Cu} limit is displated (there are 128 to 60,000 simulations).
The turns ratio might not agree with the specification exactly. For large stepdown ratios, best results are obtained if the primary has the fewest turns.
These graphs show the modelled power total power loss against the number of turns on the primary. The winding wire size is constantly changed to keep k_{Cu} constant.
Power loss includes winding loss for each winding at the RMS current given in the specification, and core loss (assuming sinusoidal current).
The valid region obeys restrictions on magnetisation (I_{m(max)} or L_{m(min)}) and flux density in the core. The values of these restrictions are shown on the Instructions tab.
The wire diameters used in the calculations are also shown.
These graphs show the modelled power total power loss against the number of turns on the primary. The winding wire size is kept constant at the specified sizes. The calculation method is identical to the fixed k_{Cu} graph.
The valid region for this graph additionally includes the specified limit on k_{Cu} (which gives a maximum N.
The value of k_{Cu} is shown. Impossible designs (e.g. k_{Cu} > 1) might be shown.
These graphs show the magnetisation and saturation limits imposed by the specification.
This graph shows the number of turns per winding against the number of primary turns. The values are calculated directly from the turns specification.
This website helps design transformers by providing estimations of loss and magnetisation as explained below. The first step is to divide the available winding area between the windings. This is done to keep the current density roughly equal throughout. This leads to the following wire diameter suggestions (for each winding \(x\) of the \(n\) windings).
The number of turns needed depends partly on the magnetisation of the transformer. The magnetising inductance is found from
where \(L_\textrm{m}\) is magnetising inductance, \(N\) is the number of turns and \(S\) is the reluctance of a core. For a transformer without an airgap, \(S={A_\textrm L}^{1}\), hence
The magnetising current is the current in this inductor. It is usually measured on the primary winding. The primary magnetising current is found from the primary voltage by
This allows us to impose limits on the design of either
or
There is also a limit from saturation of the core, although frequently losses are the main limitation (especially at high frequency). The saturaton limit is
Power loses come from two sources: the core and the windings. Core loss can be estimated using the Steinmetz equation
Winding loss (per winding) can be estimated either accounting for skin effect or not
Transformer design is a compromise between all of these constraints.