AC or DC charger: which to choose for a building

What the difference between AC and DC is

An electric car’s battery is charged with direct current (DC). An AC charger supplies alternating current to the car, and the car’s on-board charger converts it to direct current. It is the on-board charger that limits the power — most often to 7.4 or 11 kW, less often to 22 kW.

A DC charger has a built-in rectifier and delivers direct current straight to the battery, bypassing the on-board charger. That is why it charges much faster — at 50, 150 kW or more — but it is larger, more expensive and needs much greater connection capacity.

AC and DC in numbers

• Power: AC — usually 7.4–22 kW; DC — from approx. 50 kW to 150 kW and more.
• Connector: AC — a Type 2 socket or cable; DC — a CCS2 connector on a permanently attached (tethered) cable.
• Charging time from 20→80% of a 60 kWh battery (approx. 36 kWh): AC 11 kW — approx. 3.5 hours; AC 7.4 kW — approx. 5 hours; DC 50 kW — approx. 45–50 minutes; DC 150 kW — approx. 20–25 minutes (depending on the car).
• Device cost: AC — approx. 2,000–6,000 zł; DC — from several tens of thousands of złoty upwards.
• Connection capacity: several AC chargers with load balancing will usually fit on the existing connection; a single 50 kW DC charger often needs as much power as the whole building has.

Charging times are indicative: they depend on the maximum power the car can accept, the temperature and the condition of the battery. Device prices depend on the manufacturer and specification.

When an AC charger is enough

AC is a solution for destination charging — where the car is parked for several hours anyway. In an apartment block you charge overnight, at the office during working hours, at a hotel during the guest’s stay. Even 7.4 kW is entirely sufficient to have a charged battery in the morning.

• Low cost of the device, installation and documentation.
• Many points on limited power — thanks to dynamic load balancing (DLB), chargers share the available power between cars.
• Gentler charging, which is better for the battery in everyday use.
• Easy per-user billing: AC chargers with a MID meter and OCPP support work with the Domena Power system.

When DC is worth considering

DC makes sense where cars are parked briefly and vehicle turnover matters: at commercial car parks, retail and food-service sites, at depots for high-mileage fleets, or at stations along main routes. Before a decision is made, you need to check the available connection capacity and the cost of increasing it — often that, rather than the charger itself, determines whether it pays off.

At many sites, a mixed model works well: several AC chargers for destination charging and one DC charger for fast top-ups.

One system for AC and DC

Whatever you choose, it is worth connecting the chargers to a single management system. Domena Power works with AC and DC devices that support the OCPP protocol, regardless of manufacturer: it authorises users in the app, calculates the session cost according to the site’s tariff and prepares reports for billing — with no commission on energy sales.