Design of Small Transformers Based on Excel

Abstract

The electromagnetic design of small EI-type transformers couples magnetic, electric, thermal, and cost constraints through an iterative loop, and conventional practice resolves this loop either with costly commercial software whose fixed parameters are hard to align with
a given workshop process, or by manual calculation that is labour-intensive and error-prone. This paper formalises the design of 50–5000
VA EI-type transformers as a 17-step closed-loop electromagnetic calculation procedure spanning core selection, winding design, loss and
temperature-rise estimation, voltage-regulation verification, and material-cost accounting. The procedure is implemented in Microsoft Excel
using table-lookup, conditional, and array functions, so that entering customer requirements drives core and wire selection, performance prediction, and cost estimation within a single sheet without specialised software. On a 1000 VA design case, results computed by the sheet agree
with independent manual calculation to within ±3%. The tool has been applied to more than 100 transformer models in production, several of
which obtained UL and ETL certification, indicating that the approach lowers the skill and cost barrier to small-transformer design and supports rapid iteration in small and medium-sized enterprises.