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How to size a Thyristor Power Controller

The formula below provides a simple method to calculate the thyristor current for typical resistive loads. The calculated value of I should then be multiplied by 1.2 (safety margin) to allow for variations in supply voltage and other tolerances of the load.

Single Phase (1PH)

 

Thyristor current (I) = Power (WATTS)

                                      V

Example: A 9kW load across 240V AC

 

              I = 9000 = 37.5A

                    240

 

If we apply the safety margin of 20%, the thyristor current equals:

37.7 x 1.2 = 45A

 

We can therefore use a 45A, 240V AC thyristor unit

 

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