A voltage sensing,  or “across-the arc” wire feeder is very popular and very misunderstood, so let’s start from the beginning.

What is a feeder?

What is it?  A feeder, usually in a suitcase or pelican box, that can run on a constant voltage (CV) power source or, oddly enough, a constant current (CC) power source.  The latter power source is typically associated with the SMAW and GTAW processes, not wire processes.  

When this feeder is run on CV, it is a constant speed feeder where the wire feed speed (amperage) is set on the feeder and the voltage (arc length) is set on the power source.  Simple.

However, when it is running on a CC power source, the power source provides amperage and the feeder WFS knob sets a relative voltage and wire feed speed.  As contact-tip-to-work distance (CTWD) changes, which the voltage sensing lead is sensing at the work piece, voltage (arc length) changes as does wire feed speed. For example, when CTWD increases, wire feed speed (WFS) increases in an attempt to reduce the increased arc length. Conversely, when CTWD decreases, the WFS slows down in an attempt to increase the shortened arc length.  While the dance between WFS and arc length is never ending, as CTWD is always changing, the CC power source is supplying a constant current.

The Voltage Sensing Feeder

The voltage sensing feeder was designed primarily so people with CC only power sources, like old Lincoln generators, could run certain flux-cored wires.

Why use a voltage sensing feeder?  This feeder is durable, portable, and versatile (can run on both CC and CV).  They are optimal for outdoor field use.  These feeders run off arc voltage and, thus, don’t utilize a control cable.  This is a huge advantage as the wire feeder can move as far as the power cables extend. Also, control cables required for constant speed feeders are both expensive and fragile.

When NOT to Use a Voltage Sensing Feeder

Why not use a voltage sensing feeder?  This feeder, when used on a CC power source, can only run gas/ self-shielded cored wires or solid wire in a spray transfer. They cannot run solid wire in a short circuit transfer.  Most importantly, these feeders cannot be used in code quality/structural applications. This is due to the fact that the wire feed speed is always fluctuating.

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