Electric Vehicle Charger Load Balance Calculator
Installing multiple EV chargers at home (or in a small multi-tenant building) can be convenient, but it also increases the chance of overloading electrical equipment if everything runs at the same time. This Electric Vehicle Charger Load Balance Calculator is a quick rule-of-thumb tool: it estimates whether the combined charging current fits within a conservative “continuous load” limit and, if not, how many chargers you can typically run simultaneously.
What this calculator does (and doesn’t)
It does: use a simple continuous-load safety margin (commonly expressed as an 80% guideline) to estimate a “safe continuous current budget,” then compare that budget to the total current draw of your chargers.
It does not: replace a load calculation, service sizing, or an electrician’s design. Whole-home capacity depends on many other loads (HVAC, water heating, cooking equipment), panel/service ratings, demand factors, conductor sizing, breaker sizing, and local code/utility requirements.
Inputs
- Electrical panel capacity (A): the main service/panel rating (for example, 100A, 150A, 200A).
- Number of chargers: how many EVSE units you want to consider running at once.
- Continuous current per charger (A): the sustained charging current (e.g., 16A, 24A, 32A, 40A). Use the charger’s output current (often configurable) rather than the breaker size.
Formulas used
This calculator applies an 80% continuous-load budgeting approach:
- Safe continuous current budget:
L = 0.8 × P - Total charging load (if all run):
T = n × c - Maximum chargers that can run simultaneously:
m = floor(L / c)
MathML version of the core comparison:
How to interpret the results
- If total charger load (T) ≤ safe budget (L): The inputs suggest all chargers can run concurrently under this simplified rule.
- If T > L: Running all chargers at once would exceed the simplified budget. The “max simultaneous chargers” result tells you how many chargers you can typically run at full current at the same time. The remainder would need to be scheduled, throttled, or load-shared.
Worked example
Scenario: 200A panel, 3 chargers, each charging at 32A continuously.
- Safe continuous current budget:
L = 0.8 × 200 = 160A - Total charger load:
T = 3 × 32 = 96A - Compare:
96A ≤ 160A→ within this simplified budget
Interpretation: Under the calculator’s rule-of-thumb, all three could run simultaneously. In real installations you still must account for other household loads and proper breaker/conductor sizing.
Quick comparison: typical panels vs. 32A chargers
| Panel rating (A) | 80% continuous budget (A) | Max simultaneous 32A chargers |
|---|---|---|
| 100 | 80 | 2 |
| 150 | 120 | 3 |
| 200 | 160 | 5 |
Practical load-management options
- Built-in EVSE load sharing: Some systems automatically split available current across vehicles (dynamic throttling).
- Time-of-use scheduling: Stagger charging sessions overnight (e.g., one car 10pm–2am, another 2am–6am).
- Current limiting: Reduce each charger’s output current so more can run simultaneously within your budget.
- Home energy management: Coordinate EV charging with other large loads (HVAC, dryer, range) to avoid peak overlap.
Limitations & assumptions (read before relying on results)
- Not a full load calculation: This tool does not include existing household loads, demand factors, or diversity. A panel can be “200A” and still be constrained by other simultaneous loads.
- Panel rating vs. circuit/OCPD sizing: The 80% continuous-load concept is commonly applied to continuous loads and overcurrent protection sizing on circuits; applying it to a whole panel is a simplification for quick screening.
- No conductor/breaker validation: It does not verify breaker sizes, wire gauge, temperature ratings, conduit fill, voltage drop, or installation method.
- Charger current is assumed constant: Real charging current can vary due to vehicle behavior, temperature, or EVSE control.
- Local rules vary: Electrical codes, utility service limits, and permitting requirements differ by jurisdiction.
- Safety note: Use this only for initial planning. Consult a licensed electrician (and your AHJ/utility) before installation or upgrades.