Eli5 why does dc charging work so much faster than ac charging?
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Not sure what you’re getting at. All batteries are charged by DC. Plug-in wall chargers convert AC power to DC power that the device needs.
What does AC charging mean?
If you look at a DC wave on an oscilloscope, it’s flat – there’s no pulsing. If you look at an AC wave on on the same device, you’re gonna see Sin waves. In order for AC to charge DC, the sin wave needs to be rectified Into a DC wave. The conversion from AC to DC reduces efficiency and creates excess heat.
For EVs, AC charging is typically a lower voltage and don’t need heavy wires. But as the voltage increases so does the wire size, thus making the charging cable to difficult for an average person to handle.
With DC, smaller wires are able to be used for the equivalent amount of power, and the battery itself is DC, so the AC to DC converter in the car is simply bypassed. Now more power can be sent over the same sized cable that isn’t too heavy.
Most other charging cables are DC at the point they connect to the device, but that is mostly because no one wants the power brick built in as a trade off for not needing to dig through their bag for a charger when traveling.
Are you referring to cars?
All EVs have a battery that stores voltage in DC and so they must be charged as DC.
Most chargers use the AC power from your house and provide that to the car, which has an onboard converter that switches from AC to DC.
DC Fast Chargers provide much higher levels of charging power and they provide it directly to the vehicle as DC. The vehicle does not need to convert this power from AC to DC.
I am **guessing** this is done this way because it’s relatively cheap/light to have a 120v or 240v AC to DC converter on board every vehicle, but it would be more expensive/heavier to have a 480 (or more) volt AC to DC converter on every vehicle, so this converter is built into the fast charging station instead.
I’m guessing that you are asking specifically about electric car charging as that’s the only place the question really makes sense.
DC charging is faster than AC charging because more power is being supplied. You might get 11 kW from an AC charger at home, and 350 kW at a public DC charger.
So why is AC less power than DC for car charging? For AC charging, the actual charger is inside the car; the thing you plug into the car is a glorified extension cord with some safety features built in. Lower power makes the charger smaller and lighter. It converts AC power to DC (what the batteries require). It is sensible because most homes and small businesses just don’t have electrical service that can support huge amounts of power.
In DC charging, the charger in the car isn’t used. The car is connected to a charger outside the car (there’s a giant power supply in the charge station or in a nearby cabinet) and goes directly to the batter pack. They handle much more power (more than a typical house would have access too) and require larger parts that would be hard to fit inside the car.
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