In short. A telecom site runs on a minus 48 V DC plant fed by rectifiers and a battery bank, so the generator never sees the radio load directly. It sees the rectifier input, the battery recharge current and the shelter cooling, often at a remote tower with no attendant. Sizing the set for recharge plus cooling restart, planning fuel and access, and making alarms actionable matter more than the kVA figure on the canopy.
The AC to DC chain decides what the generator sees
Radio units, baseband equipment, transmission and most site electronics draw DC from a power plant at nominal minus 48 V. Rectifier modules convert the 230 V or 415 V AC input to DC, float the battery bank and carry the load. When mains fails, the battery carries the load alone until the generator starts and the rectifiers resume. At that moment the rectifiers draw not only the site load but also whatever recharge current the plant controller allows, and the shelter air conditioners or free-cooling fans restart together with them. The generator duty is therefore rectifier load plus recharge plus cooling, with the recharge block lasting hours after a deep discharge.
Modern switched-mode rectifiers present a near unity power factor and low harmonic distortion, which suits small generators. Older plants, or sites where rectifier modules have been mixed over the years, can present lower power factor and higher input current distortion, and the alternator must be checked against that. The nameplate on the DC plant and the controller settings are the data needed; see UPS and non-linear loads for the alternator side of this.
Battery autonomy and recharge demand
Autonomy and recharge are two sides of the same calculation. A larger battery rides through more short outages without a generator start, but it also draws more recharge power when the generator finally runs.
Autonomy (h) = (C × V × DoD) / P_load; P_recharge ≈ (C × r × V_charge) / η_rect
C is battery capacity in ampere-hours, V the nominal bus voltage, DoD the usable depth of discharge, P_load the DC site load in watts, r the recharge current limit as a fraction of C, V_charge the charging voltage and η_rect the rectifier efficiency. A worked example (illustrative): a site with a 2,400 W load and a 600 Ah bank at 48 V, with 80 per cent usable capacity, has about (600 × 48 × 0.8) / 2,400, or roughly 9.6 hours of autonomy. With recharge limited to 0.1C, the rectifiers draw about (600 × 0.1 × 54) / 0.95, close to 3.4 kW for recharge on top of the 2.5 kW load. Add a 1.5 tonne air conditioner at around 2 kW running with a compressor start, and the generator must carry around 8 kW running with a motor start on top. A 10 to 15 kVA set is the practical range, not the 5 kVA that the site load alone would suggest. Lithium banks accept higher recharge rates and may drive the generator size further unless the controller limits them.
Site types and what each needs
| Site type | Typical AC demand on generator | Usual architecture | Main risks |
|---|---|---|---|
| Rural ground-based tower with poor grid | 5 to 15 kW including recharge and cooling | Battery plus 10 to 20 kVA DG, increasingly solar hybrid | Fuel logistics, theft, access in monsoon, high DG hours |
| Urban rooftop site | 5 to 10 kW | Battery with shared or portable DG, structural and noise limits | Rooftop placement without structural review, acoustic complaints |
| Fibre hut or small exchange | 10 to 40 kW | Battery, AMF-controlled DG, cooling on generator | Cooling failure degrading electronics and batteries |
| Core or aggregation node | 50 to several hundred kW | N+1 DG, UPS for AC loads, dual DC plants | Transfer logic, load steps, untested redundancy |
In Telangana and Andhra Pradesh the rural tower is where most generator hours accumulate, because DISCOM outages of several hours a day in some feeders push the set into prime-like duty. Sets specified for standby ratings and run for 2,000 hours a year wear out early, so the rating should follow the measured hours. See prime power generators.
Heat, dust and the unattended shelter
Batteries lose life quickly above 25 to 30 °C, and VRLA banks in a shelter whose cooling has failed in a Telangana summer can lose a large share of their design life in one season. The shelter cooling is therefore not a comfort load; it is what preserves the autonomy the whole scheme depends on. The generator must carry it, and the alarm scheme must report cooling failure as urgently as mains failure.
For the generator itself, dust loading of radiators and air filters, high ambient derating and long periods between visits shape the specification. An acoustic canopy with adequate ventilation, an oversized fuel tank with a lockable filler and a level sensor, extended-interval filtration and a controller with remote communication are the practical minimum for an unattended site. See ambient temperature derating.
Monitoring that leads to action
A displayed status is only useful if someone knows what it means and can respond. For telecom fleets the generator controller should report run, fail-to-start, low fuel, high temperature and low battery voltage into the operator’s network operations centre, with each alarm mapped to a response: a technician visit, a fuel delivery or a remote reset. Fuel level trends identify theft and leaks; running hours trigger service. Hybrid schemes with solar and larger lithium banks cut generator hours by charging in daylight and running the set only to top up at night, but they need an energy management controller to decide when the set runs. The options are set out in solar-diesel hybrid power and remote monitoring. Reddy Generators services tower fleets across the two states under contracts that pair the monitoring data with a planned visit schedule and fuel audit.
Common mistakes
- Sizing the generator for the DC site load alone. The set stalls or trips when recharge and cooling restart arrive together after the first long outage.
- Leaving the rectifier recharge limit at maximum. The generator runs overloaded for the first hours of every run and the alternator overheats in summer.
- Treating shelter cooling as optional on generator. Battery life collapses and the autonomy the design assumed no longer exists.
- Running a standby-rated set as a prime source at a poor-grid site. Oil consumption and wear rise, and the engine needs overhaul years earlier than expected.
- Collecting alarms without assigning responses. The fail-to-start alarm is logged at 2 a.m. and nobody acts until the site goes down.
What to send us
Send the DC plant rating and rectifier module details, the battery bank capacity, chemistry and age, the measured site load, the shelter cooling rating and the grid outage pattern in hours per day. Photographs of the existing generator nameplate, the controller display and the site access route tell us a great deal about what is practical. For fleets, a list of sites with hours run and fuel consumption per month lets us identify which sets are wrongly rated. Send your service and AMC requirement or ask for a site-by-site review.
Questions engineers ask
What size generator does a typical mobile tower need?
Most single-operator ground-based sites fall in the 10 to 20 kVA range once battery recharge and air conditioning are included, and multi-tenant sites go higher. The real number comes from the rectifier recharge limit, the cooling load and the compressor start, not from the radio load alone.
Why does the generator trip a few seconds after taking load?
Usually because the air conditioner compressor and the rectifier recharge start together and the step exceeds the set’s acceptance, or because a worn battery bank draws recharge current well above the plan. Staging the compressor start and checking the recharge limit solves most cases.
Is a solar hybrid worth it at a poor-grid site?
Where the generator runs several hours a day, a solar array with a larger battery often cuts diesel use substantially and extends the engine’s life by reducing run hours. The economics depend on outage hours, fuel delivery cost and the site’s load, so they should be screened site by site.
How often should a remote-site generator be serviced?
By hours run rather than by calendar alone. High-hours sites may need oil and filter service every few weeks, while standby sites need monthly inspection and a load run. Remote hour meters and fuel sensors let the schedule follow actual use.
Technical content reviewed by Srinivas Reddy, Managing Partner, Reddy Generators. Last updated 19 October 2026.