Before a site owner picks a brand, a power rating, or a CPMS, there’s a more basic fork in the road: AC or DC. It decides the hardware cost, the installation complexity, the charging speed, and — more than any other single spec — whether the project is even viable on the site’s existing electrical connection.
The Core Difference: Where the Conversion Happens
Electric vehicle batteries store and charge in DC. The grid supplies AC. Somewhere in between, that conversion has to happen — and the only real question is where.
- AC charging sends alternating current to the vehicle, and the car’s own onboard charger (AC-to-DC converter, built into the vehicle) does the conversion. The onboard charger’s size is what caps AC charging speed — typically 3.7–22 kW for passenger EVs, regardless of how much power the charge point itself could deliver.
- DC charging does the AC-to-DC conversion inside the charging station itself, then feeds DC power directly to the battery, bypassing the car’s onboard charger entirely. That’s what unlocks 30 kW to 320+ kW charging speeds — because the conversion hardware isn’t limited to what fits inside a car.
This single distinction is why DC chargers are physically larger, considerably more expensive, and require far more substantial electrical infrastructure than AC units of comparable footprint.
Power Range and Charging Speed, Side by Side
| AC Charging | DC Charging | |
|---|---|---|
| Typical power range | 3.7–22 kW | 30–320+ kW |
| Where conversion happens | Onboard the vehicle | Inside the charging station |
| Typical full charge time (0–80%) | 4–8 hours | 20–60 minutes |
| Physical footprint | Compact wall-box or pedestal | Floor-standing cabinet, often with a separate dispenser |
| Typical install cost | Low–moderate | High (equipment + electrical works) |
| Grid connection needed | Standard single/three-phase supply | Dedicated transformer or MV connection past ~150 kW |
Cost Is Not Just the Sticker Price
The charger’s purchase price is often the smallest line item in a DC project. What usually decides feasibility is:
- Grid connection capacity. A 22 kW AC charger fits comfortably on most existing three-phase supplies. A 150–320 kW DC unit frequently requires a dedicated transformer, a new utility connection, or even medium-voltage infrastructure — a civil-works project in its own right, sometimes taking longer and costing more than the charger itself.
- Civil and electrical works. DC stations need heavier cabling, dedicated switchgear, and often a concrete pad or enclosure — none of which applies to a typical AC wall-mount.
- Cooling. High-power DC chargers generate significant heat and usually need active (liquid or forced-air) cooling in both the charger and, for ultra-fast units, the charging cable itself.
- Ongoing demand charges. Utilities often bill commercial sites partly on peak demand, not just consumption — a single DC session can spike a site’s peak draw dramatically more than a bank of AC chargers ever would, so demand-charge exposure needs to be modeled up front, not discovered on the first utility bill.
Which Use Case Needs Which
| Site type | Best fit | Why |
|---|---|---|
| Home & residential | AC (e.g. 7.4–22 kW wall-box) | Vehicle is parked for hours; charging speed matters far less than low cost and simple installation. |
| Workplace, retail & hospitality | AC, often with dynamic load balancing | Dwell time is 1–8 hours; several AC units on a shared supply cover far more vehicles than one DC unit at the same electrical budget. |
| Fleet & depot operations | Mostly AC overnight, some DC for fast turnaround | Depot vehicles typically charge on a schedule (overnight); DC is added only where a vehicle must return to service within the hour. |
| Highway & fast-charging corridors | DC (120–320 kW) | Drivers stop for 15–30 minutes; nothing below DC speed is commercially viable on a travel route. |
| Forecourt / energy-hub conversion | DC, hub-style dispensers | Replacing fuel pumps means matching fuel-like turnaround times — only DC gets close. |
| Public & municipal networks | A mix, matched to each location’s dwell time | A single network usually needs both AC (street parking, garages) and DC (transit hubs, retail centers) depending on the specific site. |
A Hybrid Reality: Most Sites Need Both
The AC-vs-DC question is rarely all-or-nothing. A retail site with a 45-minute average visit might install mostly AC for the parking area and one DC unit near the entrance for the rare visitor in a hurry. A fleet depot might run 90% of its chargers as AC overnight and keep two DC units in reserve for vehicles pulled back into rotation early. Getting the ratio right — not picking one technology exclusively — is usually what separates a well-planned site from an over- or under-built one.
What to Check Before You Decide
- What’s the average dwell time at this site — minutes, or hours?
- What’s the actual available grid capacity, and what would a DC-capable upgrade cost and how long would it take to get approved?
- Does the CPMS support both AC and DC hardware, ideally from multiple vendors, under one management platform?
- If demand charges apply, has anyone modeled the peak-demand impact of adding DC, not just the charger’s sticker price?
- Is a mixed AC/DC deployment sized so that ratio can shift later as usage data comes in, rather than locked in place by the initial electrical build?
Getting the AC/DC mix right the first time is far cheaper than fixing it after the concrete has been poured.
