How to Balance the Output Voltage of a Rotary Phase Converter

Balanced three-phase voltage — all three legs within 2% of each other under load — is critical for motor health and CNC performance. Here is how to check and improve voltage balance on your Phoenix phase converter.

Step 1 — Measure Under Load

Voltage balance must be measured while your equipment is running at full load. Measuring at no-load is meaningless — the generated leg (L3) will always look good with no load. Use a true-RMS meter and measure L1-L2, L1-L3, and L2-L3 simultaneously.

Step 2 — Calculate Imbalance

  1. Average = (V1 + V2 + V3) / 3
  2. Max deviation = largest difference between any leg and the average
  3. Imbalance % = (max deviation / average) x 100

Under 2%: excellent. 2 to 3%: acceptable. Over 3%: investigate and correct.

Common Causes and Fixes

  • Undersized converter: Most common cause. The idler cannot maintain L3 under load. Fix: upsize the converter.
  • Failed or weak capacitor: Capacitors tune the L3 voltage. A weak capacitor shifts L3 high or low. Fix: test and replace capacitors.
  • Utility imbalance: Check L1-L2 at the panel first. If utility L1-L2 is already imbalanced, the converter will reflect it. Contact your utility.
  • Long wire run voltage drop: Excessive drop on input wiring shows as imbalance under load. Fix: upsize wire gauge.

If you cannot resolve the imbalance, call (800) 417-6568 — we will diagnose it with you.

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Voltage Balance — FAQ

How often should I check voltage balance?

Check once during initial installation, then annually under full load conditions. If you notice motor overheating, nuisance trips, or CNC faults, check immediately.

Can voltage imbalance damage my equipment?

Yes — sustained imbalance above 3–5% causes motor windings to run hotter, reduces motor life, and can cause thermal overload trips. CNC servo drives are particularly sensitive.

Does Phoenix tune converters at the factory?

Yes — every Phoenix Phase Converter is individually tested and capacitor-tuned at the factory before shipping.

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Questions? Talk to an engineer.

Free sizing help. Made in Phoenix, AZ. Lifetime warranty on every unit.

Shop Phase Converters

(800) 417-6568