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Many people don't realize that a transformer labeled for use with a specific voltage will work just as well at other voltages. This calculator provides power delivered from a transformer tap when driven with other than the rated voltage.

Example: You are installing a distributed system with very long lines. To overcome line loss, you select a 140 volt system. Which transformer tap will feed 10 watts to a loudspeaker with a 70V transformer?

1. Enter values for both "Voltage Rating of Transformer" and "New Voltage"

2. Either:

  • Enter a value for "Tap Rating" to calculate the power output from the tap at the new voltage.
  • Enter a value for "Power from Tap" to calculate the correct transformer tap to achieve the desired power at the new voltage.

Equation used to calculate the data:

Pactual = (Vnew squared / Vrated squared) * Prated

Prated = transformer tap value
Pactual = new power from tap
Vrated = voltage rating of transformer
Vnew = new voltage