Phase Converter Troubleshooting: Common Problems & Solutions

Problem: Converter Won't Start

Symptom

You press the start button (or apply power), but the converter doesn't spin up. You might hear nothing at all, or a brief hum followed by silence.

Possible Causes (check in order)

1. No input power — Check the breaker feeding the converter. Is it tripped? Reset it. If it trips again immediately, there's a wiring fault.
2. Input voltage too low — Measure L1-L2 at the converter input terminals. Should be 220–240V. If less than 210V, check your supply wiring for voltage drop (undersized wire, loose connection).
3. Start capacitor failed — The converter uses run capacitors (always energized) and possibly start capacitors (energized briefly during startup). A shorted start capacitor can trip the breaker. A failed open start capacitor means no starting torque.
4. Idler motor seized — If the motor is locked up (can't rotate freely by hand with power off), the bearings may have failed. Rare, but it happens on old or heavily used units.
5. Overload relay tripped — Some converters include a thermal overload relay. If the unit got hot and tripped, wait 15–20 minutes and try again.

Problem: Breaker Trips When Converter or Load Starts

Symptom

The breaker trips when you start the converter, or when you start your equipment after the converter is running.

Possible Causes

1. Converter undersized for the load — Most common cause. The converter draws massive inrush current when your equipment starts, and that plus the converter's own startup current exceeds the breaker trip current. Solution: up-size the converter or switch to a soft-start model like the GPX Digital Series.
2. Breaker is too small — Check the breaker size against the wire and breaker table. Use a breaker sized at 250% of converter rated current.
3. Starting a very hard load (compressor, HVAC) — Hard-starting loads have enormous inrush. If using the NL Series for a compressor, upgrade to the NLA Series which is optimized for this.
4. Short circuit — A wiring fault in the converter or equipment wiring. Breaker trips are immediate (before the unit finishes starting).

Problem: Equipment Motor Runs Hot or Burns Out

Symptom

Your three-phase motor is running hotter than normal, trips its thermal overload, or burns out prematurely.

Possible Causes

1. Voltage imbalance too high — Motor overheating is the classic symptom of voltage imbalance on the phase converter output. Measure T1-T2, T2-T3, T1-T3 with a voltmeter and calculate imbalance. If over 5%, the motor is at risk. Over 10% and you'll burn motors quickly. Fix: upgrade to PL Series or re-balance the converter.
2. Converter undersized — If the converter is too small for the load, the generated leg voltage sags under load, causing the motor to draw more current to compensate — generating heat.
3. Motor wired for wrong voltage — Dual-voltage motors (230/460V) must be wired for the voltage they're receiving. If a 460V-wired motor is on a 230V converter, it runs at half design voltage. This is a common mistake.
4. Overloaded motor — The machine may be drawing more power than the motor is rated for. Check that cutting tools are sharp, feeds are not excessive, and the machine isn't jammed.

Problem: Voltage Imbalance Too High

Symptom

You've measured the three output voltages and the imbalance calculation is above 5% (for general loads) or above 2% (for CNC).

What's Normal

• NL Series: typically 3–7% imbalance, varies with load
• PL Series: typically <2% imbalance under load
• At no load (idler spinning, no equipment): imbalance can be higher — this is normal

Fixes

1. Upgrade to PL Series — The most direct fix. Enhanced filtering maintains tighter balance.
2. Ensure converter is under load when measuring — Measure balance with actual equipment running, not at no-load.
3. Check capacitor values — Degraded capacitors cause worsening imbalance over time. Capacitors can be tested or replaced.
4. Verify converter sizing — If significantly undersized, voltage imbalance will be worse under load.

Problem: Humming or Unusual Noise

Symptom

The converter makes noise beyond its normal running hum — clicking, buzzing, vibration, or high-pitched tones.

Possible Causes

1. Normal hum (low, steady) — All rotary converters hum at 60 Hz. This is normal. If you want quieter, see the GPX Digital Series.
2. Capacitor buzz — A loose capacitor or capacitor mounting bracket vibrates at 120 Hz. Tighten mounting hardware inside the enclosure.
3. Contact chatter — If you hear rapid clicking, a contactor may be chattering due to low voltage or a failing coil. Check input voltage and contact condition.
4. Bearing noise (grinding or squealing) — Worn bearings in the idler motor. The motor will need bearing replacement. This is a repair job — call us for service options.
5. Loose panel hardware — Screws or wire ties vibrating against the enclosure. Open the panel and inspect.

Problem: Equipment Starts Slowly or With Difficulty

Symptom

Your equipment starts but takes longer than normal, or makes labored sounds during startup.

Possible Causes

1. Low voltage on generated leg (T3) — The generated leg voltage may be significantly lower than T1/T2, reducing starting torque. Measure voltages.
2. Converter undersized — Not enough capacity to provide full starting current. The equipment starts but weakly.
3. Cold weather — In cold temperatures, motor insulation resistance drops and bearing grease stiffens. This is most noticeable in compressors. Let the converter warm up for a few minutes first.
4. Degraded run capacitors — Capacitors lose capacitance with age. Old capacitors may not provide enough reactive power for reliable starting.

Quick Diagnostic Reference