An improved low voltage disconnect (ILVD)

A low voltage disconnect (LVD) is a device used to protect batteries from over-discharging. Reduced life span and even catastrophic failures occur when valve regulated lead-acid batteries are over-discharged. In a typical DC power system, a power system monitor (PSM) senses the battery voltage and sends a signal to the LVD to connect when the battery voltage rises to a user-defined level. When the battery voltage drops below another user-defined level, the PSM removes the signal from the LVD and the LVD opens to prevent the batteries from over-discharging. If the PSM fails or is removed from service, the LVD opens and the telecommunication equipment shuts down even though the batteries and rectifiers are working properly. Several communication companies have purchased DC power systems without LVDs to eliminate unexpected disconnects that may bring down their systems unnecessarily. This paper describes an improved low voltage disconnect (ILVD) that was designed to minimize unwanted down times while providing protection to the batteries. The ILVD described in this paper acts like a quasi normally closed relay. The PSM sends a signal to the ILVD to open (not close) when the batteries reach a user defined level. Therefore, as long as there is system voltage the ILVD is connected and the telecommunication equipment is on line providing revenue.