Single-Phase Motor Starting Capacitor Maintenance Manual

I. Core Principles

1. ​Phase Shift Torque Generation

   • Main winding current lags voltage by 90° (phase difference)
   • Auxiliary winding current leads voltage by ~90° after series capacitance
   • Resulting in rotating magnetic field equivalent to 220V×√3≈380V mechanical output

2. ​Key Parameter Matching

   Motor Type	Standard Capacitance Range	Typical Voltage Rating
   Household appliances	1-100μF	250V/400V
   Industrial medium power	100-500μF	400V/600V
   Refrigeration compressors	150-300μF	600V/1000V

II. Fault Diagnosis Techniques

1. ​Visual Inspection
   ✓ Oil leakage (>30% capacity loss)
   ✓ Shell bulging (internal short circuit indicator)
   ✓ Fuzzy labeling (verify capacitor code interpretation)

2. ​Multimeter Measurement

   • Proper procedure: Discharge → Measure charge/discharge time
   • Capacity calculation formula: C=ΔUI×t​
     Example: 1mA discharge current, 50V drop in 15s → C=501e−3×15​=0.03μF

3. ​Bypass Verification Method
   Temporarily parallel with high-quality capacitor (≥80% of failed capacitance)
   → Normal operation confirms original capacitor failure

III. Common Pitfalls Avoidance

1. ​Aftermarket Component Risks
   ✓ Counterfeit characteristics: Brittle aluminum foil / Dielectric stratification / Abnormal ESR
   ✓ Authentication tips: Genuine manufacturers use laser anti-counterfeit codes on bottom

2. ​Special Environment Adaptations

   Operating Conditions	Recommended Capacitor Type	Special Requirements
   High temperature	Polypropylene film capacitors	20% capacity margin required
   Frequent start-stop	Metallized polypropylene capacitors	Avoid direct insertion mounting
   Continuous full-load	Parallel dual capacitors system	Include voltage balancing resistors

IV. Emergency Solutions

When no exact replacement is available:

1. ​Capacitor Parallel Connection
   Total capacitance Ctotal​=∑Ci​
   Example: 200μF needed → Use four 50μF capacitors in parallel

2. ​Star-Delta Starting
   Implement contactor-based voltage reduction for starting
   Applicable to motors above 3kW, efficiency loss ~15%