Hi everyone,


I'm currently in the process of building my own single-phase transformer, rated at 220V to 24V, 100 VA, and I need some help regarding the calculation of magnetic flux density. I've read online that for 60 Hz transformers, it's common to assume a flux density of around 1.2 Tesla, but I'm not sure if this value is always suitable or if it should be adjusted based on specific design parameters.


I already know the necessary formulas for calculating flux, turns, voltage, and core area — I just need clarification on how to properly select or justify the flux density value for my design. Should I simply assume 1.2 T, or are there cases where a different value would be better depending on factors like core type, losses, or efficiency?


Any guidance or advice would be greatly appreciated. Thanks in advance!

 

The flux density you choose would depend on the core material. What you are aiming for is to stay in the linear range and avoid core saturation, The figure of 1.2 Tesla is probably associated with the most probable choice for core material in a 60 Hz. application. This would be iron or custom steel varieties.

 

Better grade laminations will allow a higher flux density. It is vital to avoid saturation, but the next most important factor is core loss.

Core loss is equal to the square root of the fifth power of peak to peak flux excursion. So, it goes up very quickly (half way between the square and the cube) of the flux density.
You can reduce core losses by using grain oriented laminations, or by increasing the number of turns.
Increasing the number of turns requires longer, thinner wire, so increases the resistive losses in the windings.
Core loss is present all the time, but copper losss is only present when there is a load, so a Transformer that runs at full load all the time would be designed for minimum total loss, but one that is only intermittently loaded may be designed for lower core loss.

 

Operating at 50 - 60Hz, 3% Silcon steel core can be relative standard which simplifies the method of analysis to a unified approach.
Having something to compare to allows other cores to be compared. This approach used to be fairly straightforward. Usually ends with cost that exceeds annual savings.
A conservative standard reference for 3% Si-steel core material should clarify methods for Calc magnetic flux density. You have a VA rating and details for end goal.

Core Loss Datasheet - 3 percent.indd