The Victron BCD 402 is a diode based battery combiner rated at 40A, built to charge two separate battery banks from a single charge source. It suits installers working on marine, leisure and off-grid systems where two batteries need isolated charging without the voltage drop and switching complexity of a relay-based combiner. The diode design keeps the batteries electrically separated while both receive charge at the same time.

Key features of the battery isolator switch

• Combiner function, combines charge current from one source to two separate battery banks
• Rated current, 40A continuous
• Isolation, diode-based design keeps battery banks isolated from each other
• No moving parts, no relays, reducing points of failure in the charging circuit
• Weight, 0.49 kg, suited to tight installation spaces
• Compatible sources, works with a single alternator, solar controller or charger feeding two banks

How it works

Diode battery combiners allow current to flow from the charge source to each battery bank while preventing current flowing back between the two banks. A starter battery and a leisure battery can share one charging source without one bank draining into the other when the engine is off or the source is disconnected. With no moving contacts, there is nothing to wear out mechanically over the life of the installation.

The trade-off against relay-based isolators is a small forward voltage drop across the diode, typically around 0.5 to 0.7 volts. Installers should account for this when setting charge voltages, particularly where charge controllers do not compensate for the drop. The BCD 402 is rated at 40A, so size it correctly against the maximum output current of the charge source in use.

Applications

• Marine installations with separate starter and house battery banks
• Motorhomes and campervans charging a leisure battery alongside a vehicle starter battery
• Off-grid cabins with a single charge source feeding two battery banks
• Backup systems where isolation between battery banks is required for reliability

What's in the box

• 1 x Victron BCD 402 battery combiner diode unit

Installation notes

Installation should be carried out by a qualified installer familiar with DC electrical systems and battery bank wiring. Confirm the combined charge current does not exceed the 40A rating, and allow for the diode voltage drop when configuring charge controller output voltages. Correct cable sizing and fusing on each battery output is required.