May 23, 2022

Battery to Battery ( DC to DC ) Split Charging Wiring Diagram

Battery to Battery ( DC to DC ) Split Charging with Wiring Diagram

Battery-To-Battery chargers (also commonly known as DC-DC chargers) allow you to charge a leisure battery from your alternator whilst driving. They are installed in-line between the positive terminals of two batteries (one of which is connected to an alternator, typically a starter battery) and offer several benefits when compared with traditional split charge systems that utilise a Voltage Sensitive Relays.

In a traditional split charge system with a VSR will only achieve around an 80% charge state. VSRs simply allow charge to pass directly from the alternator to the auxiliary battery whereas Battery-To-Battery chargers take the alternator output and boost or reduce it to provide a stable voltage output according to a multi-stage charging profile. This provides a 100% re-charge for your leisure battery in a controlled way and typically achieves it faster than with direct alternator charging.

Using a battery-to-battery charger is the only reliable solution if you intend to re-charge a second battery in a modern vehicle that has an ECU-controlled 'smart' alternator (generally Euro 5/6 compliant engines onward). These have a highly variable voltage output that is often too low to provide a charge or (in the case of regenerative braking systems) so high that it can damage some battery types. Due to this highly variable voltage VSRs are not suitable for use with 'smart' alternators.

Battery-to-battery chargers are simple to install and will engage/disengage automatically on engine start/stop, ensuring the batteries are isolated and cannot discharge one another.