Precharge Settings

Precharge Settings

These settings deal with options specific to the precharge control logic present on Orion BMS product lines. Precharge is used to bleed off inrush current that would otherwise be present when a high capacitance system (such as a motor controller or inverter) is initially connected to a battery pack. Inrush current can cause damaging transients and may weld contactors or blow stack level fuses, all of which can cause safety hazards.

Precharge works by briefly engaging a high power resistor across the main contactor before it is closed, allowing the inrush to be bled off safely by the resistor prior to engaging. Once the precharge sequence begins, it goes through several defined stages.

Typically a circuit will have 2 contactors, called HVPOS (for high voltage positive) and HVNEG (for high voltage negative) which are placed on the corresponding poles of the battery pack. The precharge resistor is usually connected across HVPOS by means of a relay to allow it to be taken out of circuit once its role is completed. Only one contactor is technically required (HVPOS in this example), however it does leave a vulnerability if that contactor welds as the BMS will then be unable to open the pack. The software supports both 1 and 2 HV contactors.

Please see the documentation regarding precharge available on the Orion BMS website under Application Notes for details on how precharge works.

NOTE: Either one of the multi purpose outputs or the multi purpose enable pin MUST be assigned the function of "Precharge Relay Output' in order for precharge to operate.