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AC balance controls how much of each TIG cycle cleans the aluminum versus how much heats the work. Set it too far toward cleaning and the tungsten can overheat; set it too far toward penetration and oxide may remain in the weld. The right setting depends on the machine’s balance scale, the oxide on the material, the joint, and the electrode.
What AC balance does
Aluminum forms a thin, tough aluminum-oxide layer that melts at a much higher temperature than the aluminum beneath it. During the electrode-positive (EP) portion of AC, the arc helps break up that oxide near the weld. During electrode-negative (EN), more heat goes into the work, supporting penetration while reducing heat at the tungsten.
Balance sets the proportion of the AC cycle spent in EP versus EN. Controls are not labeled consistently: one machine may display EN percentage, another may display cleaning percentage, and some use a scale where higher numbers mean more EN. Check the manual before adjusting. If the display is ambiguous, consult its balance diagram rather than assuming that “more” means more cleaning.
Start with a practical range
On a modern inverter TIG machine with adjustable balance, a useful starting point is roughly 65–75% EN, or about 25–35% EP cleaning, when the machine displays EN directly. For clean, freshly brushed material, try the higher-EN end. If the machine displays EP or cleaning percentage, that same starting range is approximately 25–35% cleaning. These are starting points, not universal settings; older transformer machines may have fixed or less precisely controlled balance.
Use enough EP to remove oxide at the puddle edge, but no more than the joint needs. A wide, frosty cleaning band is not automatically a sign of a good setting. It can mean excessive cleaning, especially if the tungsten begins to ball heavily or the weld becomes hard to control.
Adjust by the weld
Prepare the joint first: remove oil, paint, and dirt, then use a dedicated stainless-steel brush on the aluminum. A balance change will not compensate for contamination. Use a clean filler rod and avoid touching its end or the tungsten to the work.
Make a short test bead using your normal amperage, electrode, and travel speed. Change balance in small steps—about 5 percentage points at a time—and compare the cleaning band, puddle behavior, and bead. A narrow, distinct band just outside the bead is generally enough for clean material. If oxide remains as dark flecks, the arc wanders, or the puddle appears dirty despite good preparation, add a little cleaning (more EP). If the cleaning band is very wide, the tungsten overheats, or the arc becomes less focused, reduce cleaning (more EN).
Balance symptoms and adjustments
| What you see | Likely cause | What to try |
|---|---|---|
| Dark specks or oxide at the puddle edge | Too little cleaning, dirty material, or poor shielding | Clean again; check gas coverage; then add EP in small steps |
| Very wide white or frosted band | Excessive EP cleaning | Increase EN balance; retest on prepared material |
| Tungsten balls excessively or loses its shape | Too much EP for the electrode and current, or an unsuitable electrode size | Reduce EP; verify tungsten type, diameter, and current capacity |
| Shallow fusion or a broad, hot puddle | Too much EP can contribute, but current, speed, and joint fit-up also matter | Increase EN modestly; check amperage and travel technique |
These clues are not proof of a balance problem. Poor shielding can cause contamination, and inadequate amperage or excessive travel speed can cause poor fusion. Change one variable at a time so you can tell what helped.
Balance is not AC frequency
AC frequency controls how quickly current alternates between EN and EP, usually measured in hertz. Higher frequency often makes the arc feel tighter and more directional; lower frequency tends to produce a broader arc. Frequency does not replace balance: changing one does not set the other’s cleaning-to-penetration ratio.
| Control | Main effect | Typical adjustment reason |
|---|---|---|
| AC balance | Cleaning action versus heat directed into the work | Adjust oxide removal, tungsten heating, or penetration behavior |
| AC frequency | Arc width and focus | Make the arc broader or more concentrated for the joint |
Match the setting to the machine and tungsten
A modern inverter with adjustable balance and AC frequency offers more control than a basic AC/DC machine with fixed balance. If you weld aluminum regularly, an adjustable balance control is worth considering; compare AC/DC TIG welders with adjustable AC balance. For occasional repairs on clean, thin stock, a simpler AC-capable machine may be adequate, though you may have fewer ways to correct a difficult joint.
Use a tungsten suited to your machine’s AC waveform and follow the manufacturer’s size and current guidance. Modern inverters can often run a pointed tungsten on AC; older square-wave or transformer machines may call for a different preparation. A large ball is not a requirement on every setup. If your tungsten overheats, first check balance, electrode diameter, and current—not just its shape. A dedicated TIG tungsten electrode assortment can be useful when comparing suitable types and sizes, but verify compatibility with your welder’s manual.
A repeatable setup
Record the machine’s balance convention, starting percentage, frequency, amperage, tungsten size, and material thickness. For a new job, begin near 70% EN if the control is EN-based, make a test bead, and adjust balance by small increments. Clean the metal again if the weld remains dirty. This simple process avoids chasing a problem caused by grease, a loose gas cup, or poor fit-up with the wrong control.
For thin sheet, avoid using extra cleaning as a substitute for controlling heat input; reduce amperage or use a foot pedal as needed. On thicker or heavily oxidized stock, preparation matters even more, and a modest increase in cleaning may help after the surface is properly degreased and brushed. Stop and correct the cause if the arc is unstable or the tungsten is contaminated; continuing with altered balance alone usually makes the weld less predictable.