• The welding current and polarities
associated with them can often be
confusing for beginners. At the
same time some experienced
welders also do not fully
understand the electric current
because there are many factors to
• This brief presentation will
highlight what AC and DC currents
are, there differences for welding
and which one is better suited for
What Is DC In Welding
• DC stands for direct current where the
electrical current flows in one direction.
Since the electrical circuit must be
continuous for the electricity to flow,
we use a ground clamp and an
electrode holder to complete the
circuit. The arc jumps between the
electrode and the metal with the
ground clamp attached, thus
completing the electrical circuit.
• Direct Current Electrode Positive
(DCEP). In this application the ground
clamp is connected to the negative
terminal while the electrode holder is
connected to the positive terminal. The
electrode will receive about 70% of the
heat and the work piece about 30%.
• The most common polarity for SMAW.
• Direct Current Electrode Negative
(DCEN). In this application the
ground clamp is connected to the
positive terminal while the electrode
holder is connected to the negative
terminal. The electrode will receive
about 30% of the heat and the work
piece about 70%.
What Is AC In Welding
• AC stands for alternating current where
the current switches direction back and
forth. Example is our standard home
outlets will provide between 110-120V of
AC power with a frequency of 60Hz. So
your available power reverses polarity
50-60 times per second. The same is true
when welding with an AC power source
or AC polarity.
• Though with increased technology some
newer machines can allow the user to
modify the output frequency, some
machines can output up to 500Hz.
AC & DC Welding
• The obvious difference is that the AC
output switches the polarity, and the
current constantly flows back and forth.
While the DC output keeps the polarity
consistent, where the current flows in
one direction. Typically AC polarity is
limited to the SMAW & GTAW
• The first SMAW power sources were
known as “buzz boxes” which were AC
machines. The switching of the polarity
caused the device to sound like a
AC Welding Advantages
• AC Advantages
• AC does not experience a voltage drop when using long
leads (ground clamp, electrode holder).
• AC SMAW machines are inexpensive compared to DC
• AC output creates a more stable arc when welding
metals prone to magnetic fields by preventing arc blow.
• AC Disadvantages
• AC creates more spatter and a less stable electric arc
when welding mild steel and stainless steel.
• Limited electrode selection.
• Weld quality in general is lower compared to a DC
• DC Advantages
• DC output provides a more stable arc compared to AC.
• Produces less spatter.
• DCEP offers excellent penetration when using the
• DCEN provides faster filler metal deposition rates, but
penetration is reduced. DCEN recommended for thin
• DC Disadvantages
• Arc blow is possible when welding magnetized metal.
• DC power sources cannot weld aluminum.
• DC machines are generally more expensive than AC
Weld Spatter More Less
Arc Stability Worse Better
Filler Metal Deposition Rates Moderate High
Penetration Moderate High
Voltage Drops Using Long Leads No Yes
Arc Blow Occurs When Welding
Weld Ferrous Metal Like Steel SMAW only All arc welding processes
Welds Aluminum AC GTAW DC GMAW/FCAW
GTAW Equipment Cost High Low
SMAW Equipment Cost Low Medium to High