What is the voltage across the electrodes on an MFDC resistance welder?

The voltages will vary depending upon the machine components and design but commonly at the open electrodes ready to weld the voltage will read about 2 volts. Depending upon the input transformer voltage and the machine this range could be 2 – 5 volts. Many MFDC transformers in the field have 9 or 13 volt outputs. Due to inherent machine resistances this voltage will drop and is frequently measured at 2 volts at the electrodes.

This 2 or 3 volts can then drive several thousand amperes through the part. OHM’s LAW enables this:

In a typical application the math for a typical current output would be:

Current I = V/R = 2 Volts / 0.0003 (300 micro Ohms) = 6,666 amperes

Current I = V/R = 2 Volts / 0.0003 (140 micro Ohms) = 14,283 amperes

Very low voltages are able to drive very high amperages.

The voltages on the electrodes in MFDC is a DC voltage with a 1000 Hz ripple. There is no zero sine wave cross and it is not a square wave.

For more information on the MFDC wave form go to another article in this blog titled:
WHY OR HOW DO MFDC CONTROLS CHANGE CURRENT FROM AC TO DC TO AC TO DC?

Reference: ENTRON Controls, LLC

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