The operational monitoring platforms of many DC charging stations frequently display contactor refusal-to-operate or unintended operation faults. In some installations, these incidents occur with troubling regularity. Certain manufacturers’ equipment is particularly susceptible, as evidenced both in platform records and in on-site inspections. Moreover, older charging stations, which have been in service for years, tend to exhibit higher rates of contactor damage. Drawing from extensive field operation and maintenance experience, the following analysis outlines the most common causes of DC contactor faults and presents targeted remedial measures.

1. Common Causes of DC Contactor Faults

1.1 Power Supply Issues

1. Many DC chargers are directly powered from a district’s public distribution transformer at 380 V or 220 V. These shared transformers experience pronounced load variations between peak and off-peak hours, leading to significant voltage fluctuations. When the input voltage swings abruptly during operation, the DC contactor may disengage unexpectedly, triggering refusal or false activation faults on the monitoring platform.

2. Loose or improperly tightened terminal bolts on the incoming power line can create poor contact. Under the heavy load of EV charging, this can cause phase loss, undervoltage, and difficulty in energizing the power module, resulting in contactor malfunctions.

3. Loose connections in the contactor’s secondary wiring — including DC input cables, feedback lines, terminal strips, relays, and power control module terminals — can interrupt control signals, causing erratic operation.

1.2 Contactor Internal Defects

1. Frequent actuation cycles or prolonged high-load service can cause contact welding or complete burnout of internal components.

2. Loose copper busbar connections on the input and output sides may overheat under heavy load, damaging internal wiring. Yellowed or charred external casings are strong indicators of catastrophic failure.

3. Certain models suffer from inherent manufacturing defects, making them prone to premature breakdown.

1.3 Excessive Temperature

DC chargers operate at high power and high current, generating substantial heat. If cooling fans fail, heat dissipation is compromised. Overheating accelerates insulation degradation within the contactor, leading to premature failure.

1.4 Improper Usage

Operators unfamiliar with correct charging procedures may repeatedly attempt unsuccessful charging cycles. Frequent switching stresses the contactor, shortening its operational lifespan.

1.5 Parameter Drift in Control Modules

Changes or instability in the power control module’s technical parameters can disrupt proper contactor actuation, resulting in refusal or false triggering.

2. Fault Remediation Strategies

2.1 Resolving Power Voltage Problems

• Verify that the charger’s supply voltage is within normal limits. If it is, power down the main breaker, wait 3–5 minutes, then re-energize — this resolves many transient faults.

• Inspect and tighten all power supply terminal bolts.

• Check the main breaker, AC contactors, and other switching devices for proper operation; replace as necessary.

• Confirm that power modules are functional and that input voltage and current are within specified ranges.

• Ensure the control board receives a stable 12 V input. If absent, test for faults in the power controller or main board. A functioning contactor coil will produce an audible click when energized.

• For high-capacity chargers, consider a dedicated distribution transformer to minimize voltage instability from shared loads. In cases of abnormal supply conditions such as phase loss, coordinate with the local utility for corrective action.

2.2 Repairing or Replacing Faulty Contactors

• Inspect for discoloration, charring, or insulation deterioration. Replace the contactor immediately if these symptoms appear.

• Ensure copper busbar terminals are adequately tightened — excessive force can strip threads or break studs.

• Test continuity across contactor terminals with a multimeter. A continuous tone indicates welded contacts; replace the contactor. In urgent situations, a light tap on the casing may temporarily release the contacts.

• Always use certified, high-quality contactors rated for the charger’s output (e.g., 250 A for 60 kW single-gun chargers, 350 A for 120 kW dual-gun chargers). Select models with a long mechanical and electrical endurance.

• During installation, ensure busbar surfaces are smooth, clean, and free from burrs to maintain optimal contact. Tighten bolts to manufacturer-recommended torque.

2.3 Managing Excessive Internal Temperatures

• Perform routine or special inspections, ensuring all cooling fans operate correctly.

• Verify that charging modules are functional and that their internal fans are running.

• Check that air inlets and outlets are unobstructed and free from dust or debris.

• Replace defective fans and modules promptly to maintain efficient thermal management.

2.4 Educating Operators on Proper Procedures

• Different chargers have varying payment and start-up processes. For example, State Grid chargers typically require the “E-Charge” app, while some privately owned units allow direct QR code payments via WeChat or Alipay.

• Post clear, illustrated charging instructions in visible locations to reduce incorrect operation and prevent unnecessary wear on the equipment.

2.5 Correcting Power Control Module Parameter Errors

• If module parameters are abnormal and cannot be restored via standard resets, engage qualified maintenance personnel or the manufacturer.

• Use service software to reload the correct firmware and test for successful charging.

• Once the system passes functional checks, clear the fault codes from the monitoring platform.

Conclusion
A refusal or false operation fault in a DC contactor is a serious malfunction, often linked to multiple interacting factors including unstable supply voltage, control board failures, power module defects, and wiring issues. Meticulous diagnosis and timely corrective action are essential. Whether stabilizing supply voltage, replacing defective components, or training operators, a structured approach reduces downtime, lowers fault incidence, and ensures reliable charging service for EV customers.