Transformer Calculations

• What is the purpose of transformers?

  To change the potential difference of electricity supply
• How do step-up transformers increase potential difference?

  They have more turns on the secondary coil
• How do step-down transformers decrease potential difference?

  They have less turns on the secondary coil
• What do the variables in the transformer equations represent?

  • \( v \): potential difference
  • \( n \): number of turns on the coil
  • \( i \): current
  • \( p \): primary coil
  • \( s \): secondary coil
• If a transformer has 18 turns on the primary coil and 54 turns on the secondary coil, what is the ratio of turns?


  The ratio is \( \frac{1}{3} \)
• Given \( n_p = 18 \), \( n_s = 54 \), and \( v_p = 45 \) volts, how do you calculate \( v_s \)?

  Use \( \frac{v_p}{v_s} = \frac{n_p}{n_s} \)
• What is the output potential difference \( v_s \) if \( v_p = 45 \) volts, \( n_p = 18 \), and \( n_s = 54 \)?

  Output potential difference is 135 volts
• If the input current \( i_p \) is 12 amps, how do you find the output current \( i_s \)?

  Use \( v_p \cdot i_p = v_s \cdot i_s \)
• What is the output current \( i_s \) if \( i_p = 12 \) amps, \( v_p = 45 \) volts, and \( v_s = 135 \) volts?

  Output current is 4 amps
• What are the two main equations used with transformers?

  1. \( \frac{v_p}{v_s} = \frac{n_p}{n_s} \)
  2. \( v_p \cdot i_p = v_s \cdot i_s \)