AC fast chargers and DC rapid chargers are two different technologies for charging EVs at speed. Both have their place, but they serve different use cases, and choosing the wrong one for your site is one of the most expensive mistakes in commercial EV charging. This guide explains the differences and how to choose the right mix.
The Technical Difference
AC chargers deliver alternating current to the vehicle’s onboard charger, which converts it to DC for the battery. The speed is limited by the onboard charger’s capacity (usually 7kW to 22kW).
DC chargers bypass the onboard charger and deliver DC directly to the battery. They are much larger and more expensive, but they can deliver 50kW, 150kW, 350kW, or more. The battery’s DC charging rate is the limit.
Charge Speeds
A typical 60 kWh EV battery:
7kW AC: 8 hours for a full charge.
22kW AC: 3 hours for a full charge (if the vehicle supports it).
50kW DC rapid: 60 to 70 minutes for 10-80% charge.
150kW DC ultra-rapid: 20 to 30 minutes for 10-80% charge.
350kW DC high-power: 15 to 20 minutes for 10-80% charge (only if the vehicle supports it).
The 10-80% figure matters because DC charging slows significantly above 80% to protect the battery.
When to Use AC
AC chargers are the right choice when:
User dwell time is 2+ hours. At that point, even 7kW AC delivers a useful charge.
The site is a workplace, residence, hotel, or long-stay car park.
Electrical supply is constrained. AC chargers need much less grid capacity per charger.
Cost per charger is the priority. AC chargers cost 5-10 per cent of DC rapid chargers.
The primary use case is topping up, not emergency quick charging.
When to Use DC
DC chargers are the right choice when:
User dwell time is under 60 minutes.
The site is a motorway service area, retail forecourt, or dedicated charging hub.
Users are on journeys rather than staying at the destination.
Grid capacity is available to support high power demand.
Users are willing to pay a premium for charge speed.
Typical Site Patterns
Different site types have characteristic charger mixes.
Supermarket: mix of 50kW DC for quick shops and 22kW AC for longer trips.
Motorway service area: exclusively DC, typically 150kW to 350kW.
Office: primarily 7kW AC, with 1-2 x 22kW for visitors.
Shopping centre: 22kW AC dominates, with a small 50kW DC offering for those who want faster charging.
Hotel: 7kW AC in every space, or select spaces.
Destination restaurant: 2-4 x 22kW AC for the 1-2 hour dining duration.
Forecourt with standalone EV hub: 150-350kW DC dominant.
Fleet depot: AC for overnight return-to-base vehicles, DC for fast-turnaround shift operations.
Cost Comparison
Equipment cost (UK 2026):
7kW AC: £600 to £950.
22kW AC: £1,200 to £2,500.
50kW DC: £12,000 to £22,000.
150kW DC: £28,000 to £55,000.
350kW DC: £60,000 to £120,000.
Installation cost (per charger):
7kW AC: £800 to £1,500.
22kW AC: £1,500 to £3,000.
50kW DC: £8,000 to £18,000.
150kW DC: £15,000 to £35,000.
350kW DC: £25,000 to £60,000.
Grid connection cost:
AC installations with modest capacity can often use the existing supply or a small upgrade.
DC installations almost always require a significant grid upgrade or new HV connection.
A single 150kW DC rapid charger needs as much grid capacity as 20-25 x 7kW AC chargers.
The Grid Connection Impact
For any multi-charger DC installation, the grid connection is the dominant design constraint.
6 x 150kW DC chargers = 900 kVA peak demand.
6 x 350kW DC chargers = 2,100 kVA peak demand.
Either installation needs a new HV connection with customer substation, adding £80,000 to £200,000 to the project cost and 4-8 months to the programme.
Load management and battery buffering can reduce the grid demand, but only within limits. A charging site that averages 50 per cent simultaneous demand still needs half the nameplate capacity.
User Experience
AC charger user experience is broadly:
Plug in, start charging, walk away, return when ready.
Low friction, low complexity.
Supports long dwell times naturally.
DC charger user experience:
Plug in, monitor charging, unplug at target state of charge.
Payment and authentication matters more because sessions are short.
Users wait during the charge or return every 15-30 minutes.
User experience design matters much more for DC rapid sites. Wayfinding, payment simplicity, and comfort during charging (seating, shelter, refreshments) distinguish good DC sites from bad ones.
Matching Charger Count to Demand
The right number of chargers depends on usage patterns.
For AC workplace charging, aim for 1 charger per 2-3 EVs expected at peak.
For AC destination charging (retail, hotel), aim for 1 charger per 10-15 parking spaces initially, scaling up based on utilisation.
For DC rapid charging, match throughput to expected daily users. A 150kW DC charger serves 15-20 cars per 12-hour day at 80 per cent utilisation. A site expecting 200 cars per day needs 12-15 DC rapid chargers.
The Right Mix for Most Sites
Most commercial sites benefit from a layered offering:
A baseline of 7kW or 22kW AC chargers for long-dwell users.
A small number of DC rapid chargers for quick top-ups and those in a hurry.
Clear signage and pricing to steer users to the right charger for their situation.
The Bottom Line
AC and DC chargers are not substitutes for each other. They serve different user patterns and have very different cost structures. Map your expected users to dwell time and charger power, then design the mix around that. Going DC-first on every site wastes money on sites where users stay long enough for AC to do the job. Going AC-only on transit sites frustrates users who need to get back on the road quickly. The right answer is almost always a mix, weighted by the actual user patterns at each specific site.