The REDARC BCDC range allows you to safely and efficiently charge a 12V auxiliary (secondary) battery from your vehicle’s alternator or solar panels. With selectable charge profiles, the BCDC ensures 100% state of charge (SOC) for a wide range of battery types, even when installed in modern vehicles with smart alternators.
Compatible battery types
The BCDC chargers are suitable for:
Flooded lead acid batteries
AGM batteries
Gel batteries
Calcium and Lead Crystal batteries
Lithium (LiFePO4) batteries
How the BCDC works with different alternator types
Fixed Voltage Alternators
Older vehicles with fixed voltage alternators can charge an auxiliary battery directly, but this has risks:
Overcharging risk: Alternators can deliver more current than the battery manufacturer recommends. A BCDC limits charge current to protect your battery.
Float charging: Alternators maintain ~14V output continuously. Most batteries require a lower float voltage once charged. The BCDC drops voltage to 13.3V when full, extending battery life.
We recommend comparing alternator voltage and current output with your battery manufacturer’s recommendations and considering the long-term effects of charging at constant high voltage.
Temperature compensating alternators
Introduced in the early 2000s, these alternators reduce output as they heat up. Result: auxiliary batteries often reach only ~70% SOC.
The REDARC BCDC solves this by providing a multi-stage charge profile, ensuring 100% battery charging while also acting as an automatic isolator to protect your starter battery.
Variable voltage/smart alternators
Modern vehicles often use smart alternators to reduce fuel consumption and emissions. These drop voltage as low as 12.3V once the starter battery is charged, which is too low to charge a deep cycle auxiliary battery.
The BCDC Classic range overcomes this by using the blue wire connected to vehicle ignition. This overrides the low-voltage cutout, ensuring consistent auxiliary battery charging.
Where to connect the blue wire
Smart alternator vehicles: Connect the blue wire to an ignition source.
Fixed or temperature compensating alternators: Leave the blue wire unconnected (or grounded).
Typical ignition connection points include:
A vehicle fuse
Cigarette lighter/12V accessory socket
Supply line to equipment like wipers, mirrors, GPS, or dashcams
Always confirm the point shows voltage with ignition on and no voltage with ignition off.
Solar input and Green Power Priority™
The BCDC Classic range includes an inbuilt MPPT solar regulator. With Green Power Priority™, solar will be used as the primary charging source whenever available, reducing alternator load.
Choosing the right BCDC model
75–200Ah battery banks: BCDC1225D (25A)
Larger single batteries or multi-battery banks: BCDC1240D (40A) or BCDC1250D (50A)
Important: Always choose a charger size within the battery manufacturer’s maximum recommended charge current. Oversizing can shorten battery life.
What’s the difference between DC-DC and BCDC?
DC-DC converter: General term for converting one DC voltage to another.
BCDC charger: REDARC’s specialised DC-DC charger, purpose-built for charging auxiliary batteries from alternator and solar inputs.
Think of it as the difference between 4x4 (general category) and Hilux (specific product).