Radio and Communications Site Duty-Cycle Battery

ScopeA radio draws a lot of current while it transmits and very little while it listens, so its battery is sized from a duty-cycle-weighted average current. The industry convention is 5-5-90 -- 5% transmit, 5% receive, 90% standby -- as radio manufacturers such as Motorola Solutions use to state battery life. The calculator computes the weighted average, the ampere-hours for the required runtime, the nameplate battery at the usable depth of discharge, the daily ampere-hours a solar array or generator must replace, and transmit's share of the energy. A temporary base station drawing 12 A transmit, 1.2 A receive, and 0.8 A standby averages 1.38 A: 99.4 Ah for 72 hours, 198.7 Ah of nameplate battery at 50% depth of discharge, and 33.1 Ah a day to recharge -- and transmit, at 5% of the time, is 43% of the energy. A repeater is where the default is wrong: it retransmits every user, so during an incident its transmit fraction can be several times 5%. At 25% transmit, 25% receive, and 50% standby the same equipment averages 3.70 A and needs 532.8 Ah -- nearly three times the battery. Enter the site's measured or expected duty. It does not account for battery temperature derating, aging, or Peukert effects (the Off-Grid Battery Bank Sizing calculator, battery-runtime), converter losses, or auxiliary equipment unless added, and it does not size a solar array. The equipment manufacturer's current specifications, the site's measured traffic, and the system's engineer govern.

Formula or tableaverage current = transmit duty x transmit A + receive duty x receive A + standby duty x standby A (default 5/5/90); Ah for runtime = average A x hours; nameplate Ah = runtime Ah / usable depth of discharge; daily Ah = average A x 24 h.

Source and editionThe 5-5-90 duty cycle convention (5% transmit, 5% receive, 90% standby) as published in radio manufacturers' battery-life specifications, for example the Motorola Solutions BPR40 data sheet, named as the default; the equipment manufacturer's current draws and the site's measured traffic named as governing.

Free accessA weighted average on currents and duties the user enters; no manufacturer table is reproduced.

What governsEstimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.

API field namestransmit_a, receive_a, standby_a, transmit_duty_pct, receive_duty_pct, standby_duty_pct, runtime_hours, depth_of_discharge_fraction, average_a, runtime_ah, battery_nameplate_ah, daily_ah, transmit_energy_share_pct

• 5-5-90 default duty 5% transmit, 5% receive, 90% standbyradio manufacturer battery-life specifications (e.g., Motorola Solutions BPR40)
• Repeater duty a repeater transmits whenever any user talks; enter measured or expected site dutyproject method
• Usable depth of discharge nameplate Ah = required Ah / usable fractionbattery manufacturer data