Does your shack inventory contain unknown power transformers? Here is a homemade tool to make identification of unknown power transformers easier and safer. It will also give you a low-voltage power source for various projects. The transformer needed to make the tool might already be in your shack inventory.
The main advantage of this tool is that it uses quite low AC voltages for testing. The AC outputs of this tool, called excitation voltages, typically range from a fraction of a volt up to a couple volts. Some operators might be tempted to use a Variac® for this purpose. Bear in mind that common Variacs are not isolated from the power line; this is a safety concern. The end result of this construction project is a low-voltage transformer with several output taps, all of which are isolated from the power line (Photo A).
This project involves the partial disassembly of an existing power transformer, one that might already be in your junk box. One of the more attractive aspects of this construction project is that only the existing secondary winding needs to be removed. The primary (line) winding, laminations, bobbin, and frame remain undisturbed. Note to educators: This low-voltage transformer can also be used as a teaching tool.
Safety Considerations
As in all projects that involve the power line, there is danger of electric shock, fire, and death. If you are a beginner, you would do well to involve an experienced radio amateur, or a licensed electrician, as a mentor throughout this project. Safety and liability are
