Can changing the turns ratio of a resistance welding transformer change the welding current?


Yes, changing the transformer turns ratio will change the current. A transformer with a tap switch works on this principal. The tap switch is wired to various points in the primary winding in order to vary the turns ratio. By changing the tap switch position the turns ratio is changed. One can choose the lowest voltage and resultant current in Tap 1 or the highest voltage and current output in the highest Tap. The number of taps and their range depend upon the transformer design.

Tap switch

Press Welder Transformer Tap Switch

Many weld transformers are manufactured with a tap switch. This tap switch gives one the ability to change the turns ratio as needed.  The net result is the output voltage changes up or down as the tap is changed.

 Transformer Tap Vs Voltage

As the output voltage changes your ability to push amps to the part also changes. Higher voltages allows for higher total amps to be delivered to the part. The general rule of thumb is:

Tap Setting Rule of Thumb

Several articles are available on this topic. Search for turns ratio or transformer tap in this blog.


References: RWMA – Resistance Welding Manual 4th Edition

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