5-2Power and Grounding Requirements
Power and grounding requirements
Typical cell site radio equipment is powered by a +24 Vdc power system. However, the primary power for a DualMode Metrocell is +27 Vdc nominal. The reason that +27 Volts is specified as the nominal voltage rather than +24 Volts is to highlight that the system requires the full float voltage level to enable it to deliver its fully rated available transmit RF output power level. When AC power is lost and the voltage level to the system is reduced to the nominal battery (that is, +24 Vdc), the power amplifiers will automatically step down their transmit RF output power. See the Dual Power Amplifier (DPA) section in NTP 411-2021-113Metrocell Radio Frequency (RF) Frame Description for details.
The power plant normally consists of a negative grounded 12-cell Valve Regulated Lead-Acid (VRLA) battery plant andAC powered battery charging units commonly referred to as the rectifiers. Under normal operating conditions, that is, when AC power is available, the batteries are maintained within their specified float voltage range via the rectifiers which must supply current to power the system and keep the batteries charged. When an AC outage occurs, the battery plant provides back-up power to the system. However, at this time, the system will experience a step drop in voltage due to a battery plant transition from the float state to the fully charged state. During the battery discharge period, the voltage supplied to the system will gradually drop from its fully charged voltage.
Under normal operating conditions an equalizing charge is not required. An equalizing charge is a special charge given to a battery when non-uniformity in voltage has developed between cells. It is given to restore all units to a fully charged condition by using a charging voltage higher than the normal float voltage and for a specified number of hours as determined by the specific voltage used. An equalize charge is also often applied when a recharge of the batteries is required in a minimum time following an emergency discharge.
A typical operating voltage range at the Power Distribution Plant of a Metrocell should not exceed the range between +22.8 Vdc to +29 Vdc. +22.8 Vdc assumes 1 V drop from the batteries to the Rack Interface Panel (RIP) and 0.8 V from the RIP to the load. The operating voltage range of a specific system could vary.
The power plant supplies two (designated as ‘A’ and ‘B’) power feeds to each Metrocell frame. Table 5-1 lists the performance requirements related to primary DC power in a Metrocell.
411-2021-111 Standard 01.01 June 1996
