DC Battery Sizing Calculator
Sizes a 48 V DC battery plant: strings required at both design and operating current, installed capacity, home-run and inter-tier voltage drop, breaker frame size, and cable-protection compliance. Method developed by PEFG — not a published industry calculator.
Aging factor per IEEE Std 485 practice. Breaker sizing applies a 1.25 continuous-load factor consistent with NEC 210.20(A)/215.3. Cable ampacity values are NEC Table 310.16 75 °C entries supplied by the user. This is a PEFG-developed sizing method — verify all results against battery and breaker manufacturer data and have the final design sealed by a licensed PE.
How the DC Battery Sizing Calculator Works
This calculator sizes a DC battery plant end to end: how many parallel strings are required to meet the load at both the full design current and the more typical operating current, the resulting installed capacity, voltage drop across the home-run and inter-tier cabling, and whether the specified breaker frame and cable ampacity actually protect that cabling. It applies the IEEE 485 aging-factor practice — battery capacity fades over service life, so a new battery is sized with margin (the aging factor Ka, typically 1.25) so it can still meet the load near end of life, not just on day one.
The sizing method itself — how strings-required, voltage drop and breaker sizing are combined into one calculation — was developed by PEFG rather than transcribed from a single published IEEE 485 worked example, so results should be treated as a PEFG-developed preliminary sizing method that applies IEEE 485's aging-factor practice, not as a reproduction of a standard's own numbers the way this site's arc flash or battery short-circuit calculators are.
Design vs. Operating Basis
The calculator reports strings required on two separate bases. The design basis uses the full rated design current with both the aging factor and a design margin applied — a worst-case check. The operating basis uses the actual continuous operating current (rated current times the operating percentage), which governs voltage drop: NEC 210.20(A)/215.3 require continuous loads to be limited to 80% of a device's continuous rating, so the operating-basis current is what the home-run and inter-tier cabling actually carries in continuous service, and that's the basis this calculator uses for its voltage-drop and breaker-sizing checks.
Related Calculators
For the fault-current side of the same DC plant — sizing breaker and fuse interrupting ratings — see the Battery DC Short-Circuit Current calculator. For rectifier, HVAC and generator capacity around the battery plant, see the DC Plant Sizing and Racks per DC Plant calculators on the main calculator suite.
For engineering consulting, DC power system design, or forensic investigations, visit pefgconsulting.com.