Low Voltage Disconnect or LVD

LVD can be configured as load or battery disconnect and normally wired as battery disconnect. The LVD disconnect the batteries from the load at the preset LVD disconnect voltage after a preset time (LVD 1 only) to prevent damage to the batteries due to excessive deep discharge. The LVD then reconnects the batteries at the preset reconnect voltage after the AC powers is restored. 

The SM45 Supervisory module provides two independent LVD channels for controlling up two LVD unit, LVD 1 and LVD2. LVD 1 and LVD 2 can have different disconnect and reconnect voltages or LVD1 can be set for timed disconnect. 

Dual LVD control is control is typical used for urgent/non urgent load disconnect prioritization. For example during an AC, power outage where the batteries are supplying load, LVD 1 can be connected to non urgent (low priority) loads and set to disconnect before LVD2. LVD2 in turn can be connected to the system batteries. Therefore the system batteries are powering the urgent (high priority) load instead of the non urgent loads. Once the batteries have discharge to level  where the preset battery termination voltage is reached, LVD2 will operate (disconnect) to prevent  deep discharge of the batteries. Standard off the shelf LVD options fall into two category.

single card 100A LVD module is used in APS3 power system

1. Rectifier Termination
2. LVD Control Termination (RJ45)
3. Fuse Fail Termination RJ45
4. Power In (LVD Supply from Backplane)
5. Load or Battery Termination

In APS6, used 200A contactors and LVD drivers card (1 LVD per Contactors). A maximum two contactors can be mounted on the inside of the integrated AC and DC distribution rear panel

LVD driver cards are soldered into the basic I/O interface board.

Each LVD Driver Card has an automatic or manual selector switch to manually override automatic control of the LVD. If the automatic or manual selector switch is set to AUTO the LVD is controlled by the SM45 supervisory module. Two contactor status LED indicate whether the LVD contacts are closed for green LED on or open for red LED on. 

1. LVD Contactor 200A
2. Auxiliary Switch Termination  on Contactor
3. Coil Termination on Contactor
4. LVD Driver Card
5. Power In 
6. Auxiliary Switch Termination on LVD Driver Card
7. Contactor Status LED
8. Automatic or Manual Selector Switch
9. Contactor Status LED
10. Coil Termination on LVD Driver Card