When someone chooses an EV charger for the first time, the question is almost always the same: \u201cHow many kilowatts does it have?\u201d The logic is understandable \u2013 more power sounds like faster charging. Yet the charger\u2019s rated power is only one link in the chain, and often not the one that sets the limit. To understand what actually determines how long charging takes, we need to start with the difference between two approaches: alternating current (AC) and direct current (DC).<\/p>\n\n\n\n
A vehicle battery stores energy in electrochemical form, and it can only be charged and discharged with direct current. This means that somewhere along the path from the distribution grid, which supplies alternating voltage, to the battery terminals, rectification must take place \u2013 the conversion of alternating current into direct current. The entire difference between AC and DC charging comes down to a single question: where this rectification happens.<\/p>\n\n\n\n
With AC charging, alternating current reaches the vehicle, and the rectification is handled by a converter built into the vehicle itself \u2013 the onboard charger (OBC). With DC charging, the rectification is performed within the station, so the battery receives current that is already direct, regulated according to the vehicle\u2019s demand. This seemingly technical detail has a decisive impact on the power at which the battery can actually be charged.<\/p>\n\n\n\n
Suppose a 22 kW AC charger is installed, with the expectation of exactly that speed. If the vehicle has an onboard charger rated at 11 kW \u2013 which is the case with a large number of models \u2013 charging will be limited to 11 kW, regardless of the fact that the infrastructure can deliver more. The limit is set by the weakest link in the chain, and with AC charging that is almost always the vehicle\u2019s OBC.<\/p>\n\n\n\n
This is why an AC charger should be sized according to the fleet that will use it, rather than the highest figure in the specification. DC charging bypasses this limitation: because the rectification is performed in the station, it delivers considerably higher power directly to the battery terminals, circumventing the modest OBC. Hence the figures of 50, 150, and even over 350 kW found on fast DC stations \u2013 levels unattainable with AC charging.<\/p>\n\n\n\n
Even when the charger and the vehicle are matched, the actual speed is determined by the behavior of the battery itself. Charging follows what is known as the CC-CV profile: in the first phase an approximately constant current flows, and as the cell voltage approaches its upper limit, the system transitions to a constant-voltage phase in which the current gradually tapers off. For this reason, charging slows down noticeably after roughly 80 percent of capacity, which is why a figure such as \u201c10 to 80 percent in 30 minutes\u201d says far more than the rated power alone.<\/p>\n\n\n\n
Temperature is another factor that is easily overlooked. At low temperatures the charge acceptance of the cells decreases, so the battery management system (BMS) limits the charging current to prevent damage \u2013 which is felt in practice as slower charging during winter. The real charging speed is therefore almost never equal to the maximum value declared on the device.<\/p>\n\n\n\n
The choice depends above all on how long the vehicle remains in one place. AC chargers rated between 7 and 22 kW are optimal where the vehicle is parked for hours anyway \u2013 in residential and commercial buildings, hotels, or parking facilities. Charging overnight or during the working day easily covers daily needs, with a lower investment and simpler installation.<\/p>\n\n\n\n
DC charging comes into its own where dwell time is short: roadside stations along traffic corridors, fleets with an intensive operating rhythm, and locations where vehicles turn over quickly. There, the higher investment is justified by the throughput such a solution enables.<\/p>\n\n\n\n
Charging speed is not a property of a single device, but the result of an entire chain \u2013 the charger, the onboard charger, the battery\u2019s characteristics, and the operating conditions. The highest rated power means little if another link in the chain does not support it.<\/p>\n\n\n\n
That is why the right question is not \u201chow many kilowatts,\u201d but \u201chow much power can the vehicle and the specific scenario actually use.\u201d The answer to that question is the starting point for selecting a solution that works as expected \u2013 without unnecessary slowdown and without over-investment.<\/p>\n","protected":false},"excerpt":{"rendered":"
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