How You Build A Transformer

by kpp

Project Description
This page will show you how to build a voltage transformer. It is not intended to be a comprehensive transformer design class but instead it is presented as a practical build this type project.

A voltage transformer is a soft magnetic device that converts a signal at one voltage to a signal at another voltage of the same frequency. A voltage transformer consists of 2 or more windings and an iron core. A voltage present on the primary winding (aka coil) of a transformer induces a magnetic flux in the core. The magnetic flux in turn induces a voltage in the secondary winding.

The core material selected dictates parameters such as core loss and magnetic saturation. For this project, we will select microsil material (aka 33XX, M6, and grain oriented silicon steel). This is a commonly selected material for power transformers since it provides relatively low losses at an affordable price. The lamination size must be determined based on the desired VA (aka Volt-Amp) capacity of the design. The number of primary turns must be calculated such that the core can support the desired voltage without saturating. The secondary turns will be calculated such that the proper voltage will appear on the secondary winding of the transformer.

Project Details
Now that the preliminary stuff is out of the way, we are ready to start building the project.
You will need the following:

  1. Acquire plastic bobbin or make a cardboard one from attached sketch.
    To create cardboard bobbin, follow these directions.
    • Draw sketch to appropriate size.
    • Cut along solid lines.
    • Fold along dotted lines.
  2. Wind the primary winding on the bobbin. This winding can be performed manually. However, to place a large number of turns on a bobbin, it is better to automate this. You can do this by fixing the bobbin to the shaft of a motor (such as a grinding wheel) and run the motor at a very slow controlled speed such that you can control the feeding of the copper wire as it is wound onto the bobbin.
  3. Place a single layer of transformer tape over the primary.
  4. Wind the secondary winding on the bobbin on top of the primary using the same technique as used with the primary.
  5. Place a single layer of transformer tape over the secondary.
  6. Assemble the laminations into the bobbin using the interleave technique. In other words place an "E" lamination from one side followed by an "E" lamination from the other side with an "I" lamination to complete that layer. Repeat this process until you can no longer fit laminations in the bobbin.