There is no standard rating to default to. The right number is worked backwards: energy per stop divided by stop length gives the average power needed — and the nameplate must sit above that average, because the charger sets only a ceiling. The car decides what it draws.
Key Takeaways
- Size backwards: energy per stop ÷ stop length = the average power needed; the nameplate sits above it.
- The charger’s kW is a ceiling — the car’s acceptance and taper set what is delivered.
- Reference points: compact DC around 20–30 kW, the DOT fast band at 50–350 kW, NEVI corridor ports at 150 kW or more.
- The supply gets a vote: a shortfall in measured headroom means a lower class or a priced supply project.
Step One: The Ceiling and the Request
A DC session is a negotiation the car controls. The charger offers up to its rating; the car requests what its battery can accept, and reduces that request as it fills. Two consequences follow. First, a higher rating only helps cars whose acceptance reaches it — a unit rated far above the visiting cars’ limits delivers the cars’ number, not its own. Second, the session average sits below the peak, so the nameplate is headroom over the average you need, never the average itself. Our explainer on how fast a DC fast charger is covers the rate curves.
Step Two: Work Backwards From the Stop
- Energy per stop. How many kilowatt-hours must a visit add? A meal top-up is a different number from a journey leg.
- Time budget. How long does the stop last? Energy divided by time gives the average power the session must sustain.
- Average to nameplate. Choose a rating above that average, because taper means the session cannot hold its peak.
- Acceptance check. Set the result against the cars you serve. If their DC acceptance clusters below your figure, the figure — not the cars — is wrong.
One labelled example, with invented inputs: a stop adding an example 30 kWh in an example 45 minutes needs a 40 kW average — a unit rated in the 50–60 kW class gives the taper headroom; a 150 kW unit’s extra capacity serves cars this stop does not attract.
Step Three: Place the Result Against the Reference Points
| Reference point | What sets it | Where it fits |
|---|---|---|
| About 20–30 kW — compact DC | Manufacturer classes below the fast band | Stops of an hour or more; a DC top-up where AC is capped by the car |
| 50–350 kW — DC fast charging | U.S. DOT’s typical band | Public stops measured in minutes, where drivers wait on the charge |
| At least 150 kW per port | NEVI standard for funded corridor stations (23 CFR Part 680) | Highway corridor sites built to the programme’s terms |
The table is a placement check, not a menu: between rows, dwell evidence — not the bigger number — breaks the tie. Why the corridor row costs what it does is covered in our piece on why DC fast charging is expensive.
Step Four: The Supply Gets a Vote
The rating is also a load the connection must carry next to the building’s own peak.
DOE-cited U.S. figures put DC fast charging at about $38,000–$90,000 equipment plus $20,000–$60,000 installation per unit, much of the installation side being supply work. A licensed electrician measures the headroom; where it falls short of the step-two answer, the options are the lower class that fits, or a supply project the utility prices in writing. The AC classes are compared in our comparison of charging levels.
Where EVDANCE’s DC Unit Sits in This Method
The EV-RHDC30K-L is the compact row made concrete: 22 kW as its product page states it, floor-standing, single connector, LCD, OCPP 1.6J, IP54. It is the answer when the stop lasts an hour or more and the cars’ AC acceptance is the bottleneck — and plainly not the answer when the method lands in the fast band. EVDANCE is a Shenzhen manufacturer founded in 2011; the unit carries its 3-year standard warranty. See our commercial charging range for the wider mix.
Frequently Asked Questions
Is a higher kW rating always the safer buy?
No. Capacity above the visiting cars’ acceptance is idle capital. The safer buy is the rating your own stop arithmetic produces, with headroom for taper.
Does a 150 kW charger charge every car three times faster than a 50 kW one?
No. The car sets the draw: a car that accepts 60 kW takes about 60 kW from either unit while its battery is low, and less as it fills. The bigger unit only shows its rating to cars that can request it.
What rating do funded corridor stations need?
Under the NEVI standards, funded corridor DC ports must deliver at least 150 kW — a programme requirement, not evidence every public site needs corridor power.
Related Reading
- How Fast Is a DC Fast Charger?
- Why Is DC Fast Charging So Expensive?
- Level 1 vs Level 2 vs DC Fast Charging: A Practical Comparison
