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Technical Notes

Guide To Transformers - Primary Configuration
It is preferable to try to obtain the required secondary voltages using separate identical primaries to be used in series or parallel. For example, two identical 115v 50 Hz primaries would be connected in series to obtain 230v 50 Hz, or in parallel to obtain 115v, 50 Hz. This arrangement is the most economical in both price and transformer size. A more versatile arrangement would be 2 identical primaries of, for example, 0-100-115V. This will provide 100, 115, and 230V, covering input voltages for places such as Japan, USA, and Europe. 

(The unused taps must then be insulated well, as these will be at their stated voltages above ground and to the other windings when the transformer is in use.)

Another option (which generally requires a larger and more expensive transformer), is a multi-tapped or ladder primary.


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