Technical guides
How to Calculate Charging-System Capacity
A repeatable method: device demand → efficiency → allocation → circuit.
Written by: LVSUN Editorial TeamTechnically reviewed by: LVSUN Editorial TeamLast reviewed: July 17, 2026
Key takeaways
- Capacity = device demand + efficiency, capped by the circuit
- Simultaneity choice (sum vs dynamic) drives cost and circuit size
The method
- 1List devices and their per-device charging power
- 2Sum peak device demand (Σ device watts)
- 3Add power-conversion overhead (supplies are not 100% efficient)
- 4Decide simultaneity: full concurrent vs dynamic allocation
- 5Check the branch circuit’s continuous limit (e.g. NEC 80% rule)
- 6Add headroom for growth
Reference points: a 120V/15A circuit ≈ 1800W (≈1440W continuous at 80%); a 230V/16A circuit ≈ 3680W. These cap what a system can draw regardless of its rating.
The key judgement
Decide whether you truly need every port at maximum simultaneously (size for the sum) or can accept dynamic allocation (size for realistic concurrency). This single choice drives most of the cost and the circuit requirement.
Capacity sizing steps
Frequently asked questions
What is the single biggest factor?
Whether you need full simultaneous per-port output or can use dynamic allocation.
Why does the circuit matter so much?
The branch circuit caps total draw regardless of the station’s rating; continuous-load rules (e.g. NEC 80%) reduce usable capacity.