5G rollouts push radio-site power consumption well above 4G levels, and the -48VDC power system is usually the first bottleneck an installer meets. This guide walks through the four sizing decisions for a 5G base station power system: load calculation, rectifier capacity with N+1 redundancy, battery backup sizing, and hybrid/temperature strategy. Product examples link to modules and cabinets available in our catalog; all figures below are illustrative and should be replaced with your equipment datasheets during detailed design.
Step 1: Calculate the site load
Start from the equipment list. A 5G site typically includes one or more active antenna units (AAU), a baseband unit (BBU), transmission equipment and auxiliaries. Take each item’s power draw from its datasheet — do not rely on generic assumptions for 5G radios, whose consumption varies strongly with configuration and traffic.
Illustrative frame: an AAU at ~1,100 W + BBU at ~350 W + transmission/auxiliaries at ~250 W gives a DC load of about 1,700 W. With a -48V bus and a wiring/rectifier efficiency of ~92%, the required rectifier output current is roughly 1,700 / (48 × 0.92) ≈ 39 A. Size for peak, not average: 5G radios have traffic-dependent peaks that must not trip your budget.
Step 2: Rectifier capacity and N+1 redundancy
Divide the total load current by the rated current of your chosen rectifier module, then add at least one spare module:
- Using 50A-class modules (e.g. Huawei R4850N2, ZTE ZXD2400 platform): a 39 A load needs 1 working module — still install N+1 (2 modules) so a failure never interrupts service.
- Using 62.5A-class modules (Vertiv R48-3000E3, Eltek Flatpack2 48/3000 HE): the same load is covered by 1 module + 1 redundant.
- Leave headroom for the next expansion step: a cabinet like the Huawei ETP48200-C5A1 (200A) or Vertiv NetSure 731 A41-S1 (200A) hosts additional modules as the site grows.
For macro sites running 4G+5G together, the load often lands at 3–6 kW; a 200A cabinet with 4–5 modules plus redundancy is then a natural fit. See the 48V cross-reference chart for module-to-cabinet mapping.
Step 3: Battery backup sizing
Battery capacity in amp-hours follows from the autonomy target:
C (Ah) ≈ (P_load × t_backup) / (V_float × DoD × η_batt)
Illustrative example: 5 kW load, 3 hours autonomy, 48V float, 80% depth of discharge, 95% battery efficiency → C ≈ 5,000 × 3 / (51.6 × 0.8 × 0.95) ≈ 385 Ah. Choose the next standard string size above the result — for example two 12V/200Ah VRLA strings in series-parallel, or an equivalent lithium pack. Lithium batteries tolerate daily cycling and high temperature better than VRLA; VRLA remains the budget default for low-cycling sites.
Step 4: Hybrid power and temperature strategy
- Weak-grid or off-grid sites: pair the rectifier system with solar input through a hybrid-capable cabinet; the NetSure 731 A41-S1 publishes solar-controller compatibility and sleep-mode energy saving for hybrid PV sites.
- Outdoor cabinets: verify the operating temperature range — the NetSure 731 A41 is specified from -40°C to +65°C, which removes the need for active cooling in many climates.
- Indoor rooms: high-density cabinets like the ETP48200-C5A1 keep maintenance front-accessible in 19-inch racks.
- Small cells and CPE-style sites: a 30A shelf such as the Huawei ETP4830-A1 with a single 2000W–3000W module covers compact loads.
Delivery checklist
- Load sheet signed against datasheets, sized for peak traffic.
- N+1 rectifier modules confirmed physically installed, not just provisioned.
- Battery strings fused, with DoD settings entered in the supervision controller.
- Monitoring (CAN/RS485/Ethernet) pointed to the NOC; alarm thresholds tested.
- Cabinet temperature derating verified against the worst ambient month.
Q: What is a 48V power system in telecom?
A: A 48V power system in telecom refers to the standardized -48V DC electrical infrastructure that powers equipment at cell sites, central offices and data centers. It comprises rectifier modules that convert AC mains to -48V DC, a battery bank on the same bus for backup, and distribution fuses feeding radios, baseband units and transmission gear. At a 5G base station the DC bus typically carries 3–6 kW through 50 A or 62.5 A rectifier modules in a 200 A cabinet such as the Huawei ETP48200-C5A1. Sizing starts from equipment datasheet currents, adds N+1 redundancy, then selects battery autonomy. Our 48V cross-reference chart maps modules to cabinets.
Q: How does a -48V DC power system work?
A: In a -48V DC power system the positive terminal of the rectifier output is connected to earth ground, making the bus voltage negative relative to ground. AC mains enters the cabinet, passes through rectifier modules (for example the Huawei R4850N2 or Vertiv R48-3000E3) that produce regulated -48 V DC, and feeds the common busbar. Batteries float on the same bus so they remain charged and instantly supply current when AC fails. A supervision controller monitors voltage, current and temperature, manages charge profiles and raises alarms. The negative polarity minimises galvanic corrosion on buried copper conductors, which is why the convention has persisted since the vacuum-tube era.
Q: Why do telecom networks use -48VDC instead of +48V?
A: Telecom networks use -48 VDC because the negative polarity—with the positive terminal grounded—suppresses electrochemical corrosion on copper conductors and cable sheaths buried in moist soil. If the negative terminal were live, stray currents would accelerate oxidation and pit the copper, eventually causing open-circuit failures. The -48 V level itself became an industry de-facto standard during the vacuum-tube era: it is high enough to deliver useful power at reasonable current, yet low enough to be safe to work on without special high-voltage protection. Modern 5G sites continue the convention because the entire ecosystem of rectifier modules, batteries and distribution panels is designed around it.
Q: How to size a telecom rectifier system with N+1 redundancy?
A: First measure the peak DC load from equipment datasheets—do not use generic assumptions, because 5G radio power varies with traffic. Divide the total load current by the rated output of one rectifier module to get the number of working modules, then add one spare for N+1 redundancy. For example, a 39 A load on 50 A modules needs one working module; install two so a failure never interrupts service. A 6 kW macro site on 62.5 A modules like the Vertiv R48-3000E3 needs one working plus one redundant. Leave physical slots in a 200 A cabinet such as the Huawei ETP48200-C5A1 for future expansion.
Q: How long do telecom batteries last on -48V backup?
A: Backup duration depends on battery capacity (Ah), load power and the allowable depth of discharge. The formula is C(Ah) ≈ (P_load × t_backup) / (V_float × DoD × η). For a 5 kW site with 3 h autonomy at 48 V, 80 % DoD and 95 % efficiency the result is about 385 Ah. Operators typically target 3–4 h for macro sites and 1–2 h for small cells. Lithium batteries tolerate daily cycling and high temperature better than VRLA, which remains the budget option for low-cycling sites. See our 48V sizing guide for worked examples and cabinet selection.
Q: Why use 48V DC power for 5G base stations?
A: 5G base stations inherit the -48 VDC architecture from decades of telecom practice. The negative-grounded bus eliminates galvanic corrosion on buried copper, the voltage level is safe for field technicians, and the global supply chain of rectifiers, batteries and cabinets is already standardised. A 5G site with active antenna units and baseband units draws 3–6 kW DC; keeping everything on -48 V avoids an extra AC-to-DC conversion stage and lets batteries ride through mains interruptions without any transfer delay. Hybrid cabinets like the Vertiv NetSure 731 A41-S1 also accept solar PV directly onto the DC bus, cutting fuel costs at off-grid and weak-grid sites.
How many rectifier modules does a 5G site need?
It depends on the measured load, not the site type. Divide peak DC load by the module’s rated output current and add one spare module: for example, a ~3.9 kW site on 50A modules needs 1 working + 1 redundant module; a 4G+5G macro site at 6 kW needs about 3–4 working modules plus redundancy on a 200A cabinet.
How much battery backup is typical for a 5G base station?
Operators commonly target 3–4 hours of autonomy for macro sites and less for small cells. Using the formula C ≈ (P_load × t) / (V_float × DoD × η), a 5 kW site with 3 hours of autonomy lands around 385–400 Ah at 48V; replace the assumptions with your actual load and battery datasheet.
Can a solar-hybrid site use the same -48V rectifier cabinet?
Yes, if the cabinet supports hybrid energy features. The Vertiv NetSure 731 A41-S1 documents solar-controller compatibility and sleep-mode savings, and the Huawei ETP48 family includes solar-ready variants; confirm the feature set with the datasheet before ordering.
Does BS Comtec supply complete 5G power kits?
Yes. BS Comtec supplies rectifier modules, embedded cabinets and battery connectivity from its Singapore stock — from 30A small-cell shelves to 200A macro cabinets — with 1-piece minimum order, 24–48 hour dispatch and configuration advice on request.
