AC/DC: Understanding Polarity

Do you know what AC (Alternating Current) and DC (Direct Current) signify on your welder and electrodes? Well, basically these terms describe the polarity of the electrical current that is created by the welder and runs through the electrode. Selecting the electrode with the correct polarity has a real effect on the strength and quality of your weld - so read on and make sure you know the difference! For that extra assurance, try the two tests at the end of the article to help you determine polarity.

The terms "straight" and "reverse" polarity are used around the shop. They may also be expressed as "electrode-negative" and "electrode-positive" polarity. The latter terms are more descriptive and will be used throughout this article.

Polarity results from the fact that an electrical circuit has a negative and a positive pole. Direct current (DC) flows in one direction, resulting in a constant polarity. Alternating current (AC) flows half the time in one direction and half the time in the other, changing its polarity 120 times per second with 60-hertz current.

A welder should know the meaning of polarity, and recognize what effect it has on the welding process. With few exceptions, electrode-positive (reversed polarity) results in deeper penetration. Electrode-negative (straight polarity) results in faster melt-off of the electrode and, therefore, faster deposition rate. The effect of different chemicals in the covering may change this condition. The high cellulose covered mild-steel rod, such as Fleetweld 5P or Fleetweld 5P+, is recommended for use on positive polarity for general welding. Some types of shielded electrodes function on either polarity, though some operate on only one polarity.

The use of the AC transformer-type welder necessitated the development of an electrode that would work on either polarity, due to the constant-changing of the polarity in the AC circuit. Though AC itself has no polarity, when AC electrodes are used on DC they usually operate best on one specific polarity. The covering on the electrode designates which polarity is best and all manufacturers specify on the electrode container what polarity is recommended.

For proper penetration, uniform bead appearance, and good welding results, the correct polarity must be used when welding with any given metallic electrode. Incorrect polarity will cause poor penetration, irregular bead shape, excessive spatter, difficulty in controlling the arc, overheating, and rapid burning of the electrode.

Most machines are clearly marked as to what the terminals are, or how they can be set for either polarity. Some machines have a switch to change polarity, whereas on others it is necessary to change the cable terminals. If there is any question as to whether or not the correct polarity is being used, or what polarity is set on the DC machine, there are two easily performed experiments that will tell you. The first is to use a DC carbon electrode, which will work correctly only on negative polarity. The second is to use Fleetweld 5P electrode, which works outstandingly better on positive polarity than on negative polarity.


Testing Your Polarity:

A. Determine polarity by using the carbon electrode

1. Clean the base metal and position flat
2. Shape the points of the two carbon electrodes on a grinding wheel, so they are identical with a gradual taper running back 2 or 3 inches from the arc tip
3. Grip one electrode in the electrode holder close to the taper
4. Set amperage at 135 to 150
5. Adjust to either polarity
6. Strike an arc (use shield) and hold for a short time. Change arc length from short to long, affording an observation of the arc action
7. Observe the arc action. If the polarity is negative (straight) the arc will be stable, easy to maintain, uniform, and conical in shape. If the polarity is positive
    (reverse), the arc will be difficult to maintain and will leave a black carbon deposit on the surface of the base metal
8. Change the polarity. Strike an arc with the other electrode and hold for a similar length of time. Observe the arc action as before
9. Examine the ends of the two electrodes and compare. The one used on negative polarity will burn off evenly, keeping its shape. The electrode used on positive polarity will quickly burn off blunt

B. Determine polarity by the metallic electrode (E6010)

1. Clean base metal and position flat
2. Set amperage at 130 to 145 for 5/32" electrode
3. Adjust to either polarity
4. Strike an arc. Hold normal arc length and standard electrode angle and run a bead
5. Listen to the sound of the arc. Correct polarity, with normal arc length and amperage, will produce a regular "crackling" sound. Incorrect polarity, with normal
    length and amperage setting will produce irregular "crackling" and "popping" with an unstable arc
6. See above for characteristics of arc and bead when using metallic electrode on correct and incorrect polarity
7. Adjust to the other polarity and run another bead
8. Clean beads and examine. With the wrong polarity, the electrode negative, you will get many of the bad bead characteristics shown in Lesson 1.6
9. Repeat several times, until you can quickly recognize correct polarity