REC Programmable Pre-charge Relay & Bi-stable Relay Driver V3.1

REC PCM V3.1: Programmable Pre-charge and Bi-stable Relay Driver for Inverter Capacitor Control

Protect Your Inverter and Contactors with Controlled Pre-charge Sequencing

The REC Programmable Pre-charge Module V3.1 is a dual-function device engineered to safeguard high-current DC systems during power-up. It first limits the inrush current when charging inverter capacitors, then activates the main contactor after a configurable delay. This controlled sequence prevents voltage sags, reduces stress on batteries and capacitors, and minimises contactor pitting—common issues in mobile, marine, and off-grid installations.

Without pre-charge, the inrush current is limited only by the total circuit resistance, which is typically very low. At 48V, the surge can be four times higher than at 12V, potentially damaging components and causing contactor welding over time. The PCM V3.1 solves this by routing current through integrated power resistors and an NTC thermistor, providing a soft-start that extends the lifespan of your entire system.

Integrated Bi-stable Relay Driver for High-Side Switched Contactors

This module includes a dedicated bi-stable relay driver designed for high-side switched latching contactors, such as the Blue Sea Systems ML remote battery switches. Unlike the REC BSLRD (which drives low-side relays), the PCM V3.1 operates on the high side, making it a direct fit for many marine and RV battery disconnect setups. The driver delivers a 6.0 A coil pulse with over-current protection, ensuring reliable latching without excessive power draw.

Key Features

• Pre-charge rating up to 120 V, 4.0 A with selectable 15 Ω or 30 Ω resistance paths plus NTC thermistor for controlled inrush
• Configurable time delay of 1, 2, 4, or 8 seconds via DIP switch to match inverter capacitor banks
• Bi-stable latching contactor drive with 100/150 ms set/reset pulse for Blue Sea ML and similar high-side relays
• Wide supply voltage range from 10 V to 80 V DC with ultra-low standby current (1 mA at 10 V)
• Reverse polarity and over-voltage protection on all inputs for robust field operation
• Compact footprint (127 x 70.6 x 35.5 mm) and lightweight (129 g) for easy integration into existing enclosures
• Supports double single-pole contactor mode for simultaneous DC+ and DC- control

Flexible Configuration for Diverse System Voltages

The PCM V3.1 operates across a battery pack voltage range of 10 V to 120 V, making it suitable for 12V, 24V, 48V, and higher-voltage DC systems commonly found in lithium battery banks. The pre-charge resistance can be selected between 15 Ω + NTC (10 Ω) on pin 5 or 30 Ω + NTC (10 Ω) on pin 10, allowing you to tailor the inrush profile to your inverter's capacitance. The DIP switch delay settings provide further customisation, ensuring the main contactor closes only after capacitors are fully charged.

Built for Reliability in Harsh Environments

Designed with a robust PCB and conformal coating, the module withstands the vibration and temperature extremes typical of RV, marine, and off-grid applications. The integrated 6.3 A slow-blow fuse on the contactor coil and 4.0 A slow-blow fuse on the pre-charge circuit add an extra layer of protection. TE Connectivity 795299-1 crimps ensure secure connections for 18-22 AWG wiring, reducing the risk of intermittent faults.

Applications

• Pre-charging inverter capacitors in lithium battery systems for caravans, motorhomes, and boats
• Driving Blue Sea Systems ML remote battery switches or other high-side bi-stable contactors
• Integrating with REC BMS or third-party battery management systems via the BMS input (0-5 V signal)
• Protecting high-current DC contactors in solar off-grid and backup power installations

Enhance Your System's Longevity

Incorporate the REC PCM V3.1 into your next build to eliminate damaging inrush currents and automate contactor control. Its programmable logic and dual-function design reduce component count and simplify wiring compared to separate pre-charge and relay driver modules. Add this module to your system today for reliable, maintenance-free power-up sequencing.