Avoiding Contactor Errors: Choosing the Right Contactor for Sevcon Gen4 Motor Controller

BorgWarner Sevcon Gen4 motor controllers can manage their own line contactor however not all contactors are compatible. The low-voltage models Size 2, 4, and 6 feature three configurable analog outputs designed to operate line contactors or other low-power loads.

Using an unsuitable contactor can lead to coil overheating and failure. The Gen4 may detect an unsuitable contactor and trigger a fault condition. A common fault code is 6 LED flashes or 0x5183 Analog Output Over Current.

Each analog output can deliver a reduced voltage from 12V up to battery voltage using pulse-width modulation (PWM). For example, a 48 V supply running at 50% duty cycle produces an effective 24 V output.

Note: When testing analog outputs without a connected load, standard multimeters typically display full battery voltage due to their inability to interpret PWM signals accurately.

There are two main types of contactor coils: intermittent-duty and continuous-duty. Intermittent coils are typically designed to receive a PWM signal at their rated voltage, while continuous coils are intended to operate with a constant voltage.

In Gen4 LV applications, continuous-duty coils are generally more suitable—unless an intermittent-duty coil is specifically rated to handle the full battery voltage.

For example, with a 48 V battery, if a 12 V output is configured, the controller will apply a 25% duty cycle of 48 V. This means the contactor coil is exposed to a 48 V PWM waveform, which could damage a 12 V intermittent coil. A 12 V continuous-duty coil will more likely tolerate such conditions.

Ultimately, coil selection comes down to staying within the manufacturer’s specifications. Since ratings are often unclear on datasheets, it’s best to confirm suitability directly with the manufacturer.

We recommend the following contactor, which has proven to operate reliably with the Gen4 controller: Rincon Power RXR25B1BX