Enerpro’s VR31 Auxiliary Generator Three-Stage Charge Voltage Regulator Module is a direct replacement for the VR10 - VR16 EMD auxiliary generator field controllers used in EMD Auxiliary Generator equipped locomotives (prior to SD70Ace and SD70M-2). The VR31 provides battery manufacturer recommended three-stage battery charging profile for longer battery life, faster charging, reduced water consumption and compatibility with flooded lead acid (FLA) valve regulated lead-acid (VRLA) and lithium-ion batteries.  A novel solid-state circuit replaces a problematic bootstrap contactor to power-up the generator from residual magnetism. The VR31 is compatible with both ac and dc auxiliary generators.


  • Three-stage Battery Charging
  • Longer Battery Life
  • Reduced Failure to Start Events
  • Faster Charging
  • Reduced Water Consumption
  • Simple Installation
  • Compatible with Flooded Lead Acid, Valve
    Regulated Lead Acid, and Lithium-ion Batteries
  • Compatible with both AC and DC Aux Generators


System Description

The advent of locomotive automatic engine stop and start systems has brought the benefits of decreased fuel consumption and air emissions but also increased the demands on starting batteries. The much more frequent discharge-charge cycles combined with constant voltage VR10- VR16 voltage regulators has resulted in much shorter battery life, battery plate sulfation, and reduced charge capacity. The operational impact is increased failure to start events and more frequent battery replacements. The VR31 solves these problems by providing battery manufacturer recommended 3-stage battery charging.

VR31 module
The VR31 module is a direct replacement for the VR10-16 series auxiliary generator voltage regulators. Locomotives equipped with the DVR300 voltage regulator require an additional mounting cage and wiring harness adapter for installation. The VR31 uses auxiliary generator voltage feedback, like the VR10, but also uses battery current feedback to provide optimum battery charging. The current sensor provides feedback required to limit current at the start of the charge cycle and to determine when the battery is 95% charged for transition to the float stage. VR31 design incorporates several failure mode protection features that ensure high operational reliability.

Shorted PWM Transistor Protection
At high engine speed, the auxiliary generator will produce dangerously high voltage if the PWM transistor or the bootstrap transistor becomes shorted or if either transistor is turned on continuously due to a component failure. In this event, an over-voltage comparator trips the panel mounted circuit breaker if the auxiliary generator voltage exceeds the over-voltage trip threshold.

Loss of Current Feedback Protection
If the current sensor fails or the current signal to the VR31 becomes shorted or open, the VR31 immediately transitions to the 72V float voltege. A current sensor fault light on the VR31 also lights and an output signal is sent to the locomoitve. This fail-safe feature protects the battery from overcharging while still allowing the locomotive to operate until the next maintenance cycle.

EBCS-2 Current Sensor
The EBCS-2 current sensor is installed on the BTN battery cable directly behind the knife switch. By providing isolated battery current feedback to the VR31, the system is able to provide proper charging irregardless of load switching. The EBCS-2 is powered from nominal 74V output of the Auxilliary Generator and has built in failure detection and fail-safe circuitry.

General Products
Locomotive Products