Controlling Alternators in Victron Lithium Battery BMS Systems

Victron lithium battery BMS systems have two signals that control charging and load circuits. When an abnormal battery condition occurs, each of the signals can respectively disable charge sources and system loads to protect the battery.

Alternator charging of lithium battery banks can severely stress a standard alternator so one should upgrade to a more suitable alternator product. Even when replacing the standard alternator with a unit designed for heavy-duty charging, we recommend using a temperature-controlled alternator regulator that will back off the charging if the alternator gets too hot. For most cruising vessel applications, the following types of products are advised.

• Balmar 618 alternator regulator
• Balmar alternator temperature sensor
• Balmar XT small frame alternators

Under no circumstances should the alternator be disconnected from the battery while charging by means of a battery switch or relay type contactor. Directly interrupting the charge current can and will blow out the alternator diodes.

A prevalent method is for systems where the alternator connects to a start battery and then a Victron Li-CT Battery Combiner device is used to cross charge the house battery. The battery combiner is enabled when the right voltage conditions are met and only when the BMS signals a healthy condition for charging. Although the primary charge current to the lithium battery is interrupted, the start battery can absorb the resulting voltage spike to a certain degree. This method works fine and is a system of choice when doing a Lithium Battery System Upgrade.