What is the Advantage and Disadvantage of AC Fast Charger for EV

EV charging stations are becoming more commonplace. Most charging stations you see are AC chargers. Until recently, AC chargers have been the only option. But in recent years new technology known as DC Fast Chargers has been developed allowing companies to apply a different type of technology to charge vehicles faster than the standard AC chargers

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The proportion of DC fast chargers to AC chargers is growing. But for many people, the question remains AC vs DC EV charging, which charging station should be used for fleet vehicles? Should companies with depots install AC chargers or DC chargers? That’s the question we’ll seek to answer in this article.

 To help introduce you to the world of AC vs DC and their differences, there are two key things to remember:

• The electricity from the grid (like a wall socket in your home) is always AC (alternating current).
• Electric Vehicle Batteries always store and use DC (direct current).

AC and DC operate differently. They flow in different ways, serve different purposes, and impact charging speed and efficiency in unique ways.

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What is the Difference Between AC and DC Charging Current?

What is AC Charging for Electric Vehicles

Alternating current (AC) power can be described simply as the standard electricity that comes out of power stations and travels along power lines to homes and other buildings, sometimes referred to as mains or utility power.

What is DC Charging for Electric Vehicles

Direct current (DC) power, as the name suggests, is the electric current that moves in a straight line.

Direct current can come from multiple sources, including batteries, solar cells, fuel cells, petrol generators, and some modified alternators. DC power can also be "made" from AC power by using a rectifier that converts AC to DC.

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Differences between AC vs DC EV Chargers

Your outlet delivers AC power, and your vehicle battery needs DC power.

The only way to achieve this is to convert AC power into a DC power output. This is what we call an AC to DC converter (AC-DC converter).

AC EV Chargers require you to build this converter into your vehicle. This means that the vehicle has its own small AC-DC converter. So, the vehicle receives AC power from the charge point, then the vehicle converts it to DC power.

DC EV Chargers require you to build this converter into your charge point. This means the chargers have their own built-in AC-DC converter, and the vehicle receives DC power directly. No conversion is required inside the vehicle.

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EV Charging Curves

The key difference between AC and DC charging curves lies in how much power the battery can accept over time.

AC Charging Curve

AC chargers rely on your car's built-in converter, which typically handles a constant power level. This translates to a flat charging curve on a graph.  The car steadily charges the battery at a set rate until full.

DC Charging Curve

DC fast chargers have a more powerful converter and deliver DC power directly to the battery. However, for battery health reasons, the ideal charging rate isn't constant. DC charging curves typically start high, allowing for rapid initial charging. As the battery fills up, the curve slopes downward, reducing the power input to prevent overheating. This creates a decreasing, curved line on a graph.

Are Car Batteries AC or DC?
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Batteries need DC power. And there is a simple reason. Just like any other battery - a car battery uses and provides DC power. This means the load flows in one single direction and is stored using a chemical process.

As mentioned, AC current changes direction periodically. To store AC, a battery’s terminal needs to change polarity (+ and -) at the same speed, which is not possible. Connecting an AC supply to a battery to store AC power means the battery charges only during the positive half-cycle and then discharges during the negative half cycle.

In other words, there is no way a car can store AC power in a battery.

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Why is DC Charging Faster than AC?

The faster you want to charge a battery - the more power you need to provide. Fast charging is usually above 50 kW, and slow charging typically between 1-22 kW to provide more power when charging a battery, you need a much larger AC-DC converter.

The problem is - converting high power from AC and DC is expensive. A large converter easily costs USD 10,000.

This high-power charging is best carried out with the converters built into the charging station rather than the vehicles so you’re not dragging around heavy and expensive converters dragged around with you in your car.

That’s the main reason why DC chargers appear to be faster than AC chargers. They aren’t really any faster; it’s just much easier and cheaper to generate high-power DC output within the charger rather than convert the output from an AC charger in the vehicle itself.

When do I Choose AC EV Charging?

AC charging is best for regular charging needs such as:

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• Home
• Work
• Errands

Pros of AC Charging

• Cost-effective: AC chargers are generally less expensive to install and maintain.
• Widely available: AC charging stations are more common and can be found in homes, workplaces, and public parking areas.
• Gentler on battery: AC charging is typically slower and less stressful on the battery, which can help prolong its lifespan.

Cons of AC Charging

• Slower charging: AC charging takes longer to fully charge an EV compared to DC charging.
• Limited power output: AC chargers have a lower power output, which can be a drawback for EVs with larger batteries or for drivers who need a quick charge.

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When do I Choose DC EV Charging?

DC chargers cost a lot more than AC chargers. DC chargers require more space and require much more complex spare parts to facilitate processes such as active cooling.

In addition, high power charging requires a high power connection to the grid. With a typical residential grid connection, you won’t be able to install a DC charger.

DC fast charging is best for situations where time is tight such as:

• Road Trips
• Low Battery Emergencies
• Fleet Vehicles

Pros of DC Charging

• Faster charging: DC chargers can significantly reduce charging time, making them ideal for long-distance travel or when time is limited.
• Higher power output: DC chargers deliver more power, allowing for faster charging of EVs with larger batteries.

Cons of DC Charging

• Expensive: DC chargers are more expensive to install and maintain due to their complex technology and higher power requirements.
• Less available: DC charging stations are less common and may be harder to find, especially in residential areas.
• Potential battery degradation: Frequent use of DC fast charging can generate heat and stress on the battery, which may lead to faster degradation over time.

The rule of thumb is: Install DC chargers when you need fast charging and install AC chargers when you don’t.

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Conclusion

DC fast chargers are ideal for charging EVs that need to be back on the road quickly. But they are more expensive to install and maintain than AC chargers.

If time is of the essence for your fleet, then DC chargers are going to be the best option.

If you have a mixed fleet of vehicles - i.e., some that need fast charging and some that don’t, then a mixture of AC and DC chargers is best.

Either way, smart charging software for electric vehicles can help fleet managers to offset some or all of the extra initial outlay by reducing ongoing energy costs.

Read more about AC and DC charging here: How to mix AC and DC charging stations?

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AC (Alternating Current) and DC (Direct Current) charging stations are two common types of electric vehicle (EV) charging infrastructure, each with its own set of advantages and disadvantages.

Advantages of AC Charging Stations:

Compatibility: AC charging stations are compatible with a wide range of EVs because most electric vehicles have onboard AC chargers. This means that a single AC station can serve multiple types of EVs, making it more versatile and accessible.

Cost-Effective Installation: AC charging infrastructure tends to be less expensive to install compared to DC stations. This is because AC charging utilizes the existing electrical grid infrastructure more efficiently, reducing the need for costly upgrades.

Grid-Friendly: AC chargers are generally more grid-friendly than DC chargers. They draw power from the grid in a smoother and more predictable manner, reducing the risk of sudden spikes in demand and minimizing stress on the electrical grid.

Slower Charging: While AC charging is slower than DC charging, it is adequate for many daily charging needs. For EV owners who primarily charge at home or work and have ample time for charging, the slower pace may not be a significant drawback.

Disadvantages of AC Charging Stations:

Slower Charging Speed: AC chargers typically offer lower charging speeds compared to DC chargers. This can be a disadvantage for EV owners who require fast charging, especially on long trips.

Limited Compatibility with High-Power Charging: AC chargers are less suitable for high-power applications, making them less suitable for fast-charging stations along highways or in areas where quick turnaround times are essential.

Advantages of DC Charging Stations:

Faster Charging: DC charging stations provide much faster charging speeds compared to AC stations. They are ideal for EV owners who need rapid top-ups, making them essential for long-distance travel and busy urban areas.

High-Power Capabilities: DC chargers are capable of delivering high-power charging, which is crucial for quickly replenishing an EV’s battery. This feature is especially important for reducing downtime at public charging stations.

Compatibility with High-Capacity Batteries: DC charging is well-suited for EVs with larger batteries, as it can provide the necessary power to charge them quickly and efficiently.

Disadvantages of DC Charging Stations:

Higher Installation Costs: DC charging infrastructure tends to be more expensive to install than AC stations. It requires specialized equipment, such as transformers and inverters, which can drive up the overall installation cost.

Limited Compatibility: DC charging stations are often specific to certain EV models or charging standards. This can result in reduced versatility and accessibility compared to AC stations.

Grid Stress: DC fast chargers can put more strain on the electrical grid due to their higher power requirements. This can lead to increased demand charges for the charging station operator and potential grid issues if not managed properly.

In conclusion, both AC and DC charging stations have their own advantages and disadvantages. The choice between them depends on factors such as charging speed requirements, cost considerations, and compatibility with specific EV models. A balanced charging infrastructure often includes a mix of both AC and DC stations to cater to the diverse needs of EV users.

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Post time: Sep-07-