Chargers
9
EV Charging Station Design Calculator
Size the transformer and distribution for an EV charging station — demand load, simultaneous-use factor, supply voltage and a reference bill of materials.
For consultants and installers sizing the electrical service and transformer for AC and DC EV charging stations.
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Worked example
A pre-computed reference example (crawlable — no JavaScript required). Enter your own parameters above for a live result.
Worked example — 4×7 kW + 2×22 kW AC + 2×60 kW + 1×120 kW DC
Station demand
250 kW
263 kVA · 312 kW connected · diversity 0.8
Transformer
315 kVA
Feeder
10 kV
Line current
379 A
Load & transformer sizing
| Quantity | Value |
|---|---|
| Connected load | 312 kW (Σ chargers × rated power) |
| Diversity factor | 0.8 (simultaneous-use factor) |
| Demand load | 312 × 0.8 = 250 kW |
| Demand (apparent) | 250 ÷ 0.95 = 263 kVA |
| Required transformer | next standard ≥ 289 kVA → 315 kVA |
| Supply voltage | 10 kV (MV feed) — recommended for this size |
Recommendation
Design note
10 kV MV service with a 315 kVA distribution transformer
DC fast-charging load is peaky — consider a battery energy-storage system for peak shaving (reduce demand charge).
Pricing basis
Charger unit prices are from the ev-charging-stations price reference (FOB Qingdao, medium confidence); exact models are quoted per project.
Bill of materials
| Equipment | Spec | Qty | Subtotal |
|---|---|---|---|
| AC charger (7 kW) | 7 kW · 1-phase/3-phase | 4 | POA |
| AC charger (22 kW) | 22 kW · 3-phase | 2 | POA |
| DC fast charger (60 kW) | 60 kW · CCS/GB-T | 2 | POA |
| DC fast charger (120 kW) | 120 kW · CCS/GB-T | 1 | POA |
| Distribution transformer | 315 kVA · 10 kV / 0.4 kV · S13 | 1 | POA |
| Total equipment (reference) | POA |
Worked example — 4×120 kW DC fast-charging hub
Station demand
432 kW
455 kVA · 480 kW connected · diversity 0.9
Chargers
4
Transformer
630 kVA
Feeder
10 kV
Line current
26 A
Load & transformer sizing
| Quantity | Value |
|---|---|
| Connected load | 480 kW (Σ chargers × rated power) |
| Diversity factor | 0.9 (simultaneous-use factor) |
| Demand load | 480 × 0.9 = 432 kW |
| Demand (apparent) | 432 ÷ 0.95 = 455 kVA |
| Required transformer | next standard ≥ 500 kVA → 630 kVA |
| Supply voltage | 10 kV (MV feed) — recommended for this size |
Recommendation
Design note
10 kV MV service with a 630 kVA distribution transformer
DC fast-charging load is peaky — consider a battery energy-storage system for peak shaving (reduce demand charge).
Pricing basis
Charger unit prices are from the ev-charging-stations price reference (FOB Qingdao, medium confidence); exact models are quoted per project.
Bill of materials
| Equipment | Spec | Qty | Subtotal |
|---|---|---|---|
| DC fast charger (120 kW) | 120 kW · CCS/GB-T | 4 | POA |
| Distribution transformer | 630 kVA · 10 kV / 0.4 kV · S13 | 1 | POA |
| Total equipment (reference) | POA |
How it was calculated
- · Connected load: Σ (charger count × rated power).
- · Demand load: Pdemand = Pconnected × diversity factor.
- · Demand kVA: S = Pdemand ÷ power factor.
- · Transformer: next standard kVA ≥ S × 1.1 (design margin).
- · Line current: I = S ÷ (√3 · U).
Referenced standards
| Standard | Scope |
|---|---|
| IEC 61851 | Electric vehicle conductive charging system |
| GB/T 51313 | Technical standard for EV distributed charging facilities |
| GB/T 18487 | Electric vehicle conductive charging system (China) |
Frequently asked questions
How do I size the transformer for an EV charging station?
Sum the charger ratings with a coincidence factor: AC Level 2 chargers are 7-22 kW each, DC fast chargers 60-360 kW. A 10-charger DC station can peak near 500-1200 kVA. Size the Transformer to the coincident peak plus margin, per IEC 61851 and GB/T 51313. The calculator computes demand and transformer kVA.
What is the difference between AC and DC EV charging?
AC charging (Level 2, 7-22 kW) uses the vehicle's onboard charger and takes hours; DC fast charging (60-360 kW) bypasses it and charges to 80% in 20-40 minutes. DC stations need much larger electrical supply and cooling. The calculator models both and sizes supply accordingly.
What is the typical demand factor for an EV charging station?
EV charging is time-correlated, so the demand factor is higher than other loads — 0.7-1.0 for a busy DC fast-charging hub. A fleet depot charging overnight runs 0.8-1.0 simultaneously. The calculator applies a coincidence factor to avoid undersizing the supply.
What supply voltage does a DC fast charging station need?
A small station (a few 60-120 kW chargers) runs on 0.4 kV; a larger hub (500 kW-1.5 MW) needs a 10 kV feed and a dedicated transformer, per GB/T 51313. The calculator selects the supply voltage and transformer from the aggregated charger load.
What charging standard should the station support?
Global standards: CCS (Combined Charging System) and CHAdeMO for DC, GB/T 20234 for China, and Type 2 for AC. A station serving mixed fleets usually offers CCS2 DC plus Type 2 AC. The calculator's design basis assumes IEC 61851-compliant chargers.
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Reference estimates (FOB Qingdao, EXW) for preliminary design only — not a final quote. Confirm sizing against your project and local standards.
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