Electrical system: The Orion XS can charge the starter battery in an emergency

Normally, a battery-to-battery charger only works in one direction: whilst the engine is running, the alternator supplies power to the starter battery. The B2B charger draws this energy and uses it to recharge the auxiliary battery. How this principle works in the Victron Orion XS 12/12-70 with a charging current of up to 70 amps BOOTE has already shown how it works.

With firmware version 1.15, the Orion XS can now switch direction in exceptional circumstances: if the starter battery’s voltage is no longer sufficient to turn the engine over, the unit briefly draws power from the service battery to top it up. Victron calls this function ‘Emergency reverse charge’. It is available on the Orion XS 12/12-50, the Orion XS 12/12-70 and the the versatile Orion XS 1400 available.

Charge for 15 minutes, then start the engine

The emergency start function is activated in the VictronConnect app. To do this, the user taps the starter battery icon on the status screen. The Orion XS then charges in reverse for 15 minutes, i.e. from the service battery to the starter battery.

This is followed by a five-minute break. During this time, the charger is switched off to allow the voltage of the starter battery to stabilise. Victron recommends starting the engine as soon as the app displays ‘Battery ready’. However, this does not necessarily mean that a start attempt will be successful: the function only transfers a limited amount of energy and is no substitute for a faulty or aged starter battery.

Recharge current remains limited

The recharge current is limited to a maximum of half the rated charging current of the respective Orion XS. If a lower current limit is specified in the configuration, this lower value applies. For the 50-amp model, this means a maximum of 25 amps is possible; for the 70-amp model, a maximum of 35 amps.

To prevent the service battery from becoming too deeply discharged, the Orion XS reduces the reverse charging current if its voltage drops too low. The starter battery is charged to a maximum of 14.4 volts. For the Orion XS 1400 with a 24-volt starter battery, the limit is 28.8 volts. During reverse charging, as few electrical loads as possible should be powered from the service battery.

Only when the forward charge is switched off

Reverse charging is not available during the normal charging process. The Orion XS must be in charger mode, but must have already completed its forward charging cycle. This is the case, for example, if the input voltage is too low or if the motor run detection system detects that the motor is not running.

Even a unit that has been switched off via the remote on/off function can use the emergency start function. However, caution is required when operating several Orion XS chargers in parallel: Victron recommends either switching all units to reverse charging at the same time or switching off the remaining chargers. Otherwise, the units may work against each other, causing energy to circulate within the system rather than effectively supporting the starter battery.

Practical help, but not a solution to the root cause

For motorboat owners, this function is particularly useful in an anchorage or after the boat has been moored for a long time. It can help if the starter battery has become too weak due to a connected electrical load, unnoticed discharge or a prolonged period of inactivity.

However, the emergency start function is no substitute for investigating the cause. If the engine only starts again after reverse charging, owners should check the starter battery, the alternator, the isolating relay and any continuous-current consumers. Particularly in the case of complex electrical systems, it is worth systematically checking the charging circuits and the DC distribution.

Update via the app or VRM

This requires Orion XS firmware version 1.15 and at least version 6.43 of the VictronConnect app. The firmware update can be installed via VictronConnect or remotely via the VRM portal. For the Orion XS 1400, you must specify whether a 12- or 24-volt starter battery is connected before using it for the first time. It is essential that this setting matches the actual nominal voltage of the starter battery.

Book recommendation

Perfect boat electrics It is also specifically aimed at motorboat owners who wish to gain a better understanding of, maintain or upgrade their electrical systems. The book explains batteries, power management, cable connections, measuring instruments, and direct and alternating current on board, with numerous step-by-step illustrated guides.

Have you already made provision on board to support the starter battery from the service battery if the engine fails to start?