How to Fix a Voltage Imbalance on a Rotary Phase Converter

Voltage imbalance on a rotary phase converter — where one or more output legs reads significantly different from the others — is a diagnosable, fixable problem. Here is a step-by-step guide.

Step 1 — Confirm the Imbalance Is Real

Always measure under load. Measure L1-L2, L1-L3, and L2-L3 with your equipment running at full load, using a true-RMS voltmeter. No-load readings are meaningless — the generated leg (L3) always looks good at no load.

Calculate imbalance: Average = (V1+V2+V3)/3. Max deviation = largest leg difference from average. Imbalance % = (max deviation / average) x 100. Over 3% warrants investigation.

Step 2 — Check the Utility First

Measure L1-L2 directly at your main panel under load. If this reading itself is low or unbalanced, the problem is upstream of your converter — contact your utility company. A converter cannot correct utility imbalance.

Step 3 — Check for Undersizing

If your converter is undersized for the connected load, L3 will sag under full load. Verify your converter HP rating vs. your equipment HP x load multiplier. If the math shows you are over capacity, you need a larger converter — no amount of capacitor tuning will fix this.

Step 4 — Inspect and Test Capacitors

Run capacitors tune the L3 voltage. A weak or failed capacitor causes L3 to read high or low. To test:

• Discharge capacitors completely before touching — they hold lethal charge
• Test capacitance with a capacitor meter — compare to the label value (within 5% is acceptable)
• Visually inspect for bulging, cracks, or oil leakage
• Replace any capacitor outside spec — use the same microfarad rating and voltage rating

Step 5 — Check Wire Connections

Loose or corroded terminals add resistance and create voltage drop that appears as imbalance. Inspect and tighten all terminals — both on the converter and at the equipment disconnect.

Still Not Fixed?

Call (800) 417-6568 — our engineers can walk through the diagnosis with you on the phone. Bring your measurements and we will find the root cause.

Related Articles

• How to Size a Rotary Phase Converter
• Rotary vs Digital
• Phase Converter FAQ

Fixing Imbalance — FAQ

How do I know if my capacitors are bad?

Signs: voltage imbalance on L3 that is new or worsening, visible bulging or leakage on the capacitor body, or measured capacitance outside 5% of the label value (test with a capacitor meter).

Where can I get replacement capacitors?

Call Phoenix at (800) 417-6568 — we will identify the correct capacitor for your unit and ship it. We stock capacitors for all Phoenix Phase Converter models.

Is voltage imbalance covered under warranty?

Capacitor replacement is covered under Phoenix's lifetime warranty. Call us and we will take care of you.

Related Articles

• How to Size a Rotary Phase Converter
• What Is a Rotary Phase Converter?
• Rotary vs Digital Phase Converters
• Phase Converter FAQ