American standard charging pile certification (III) – Design details of AC piles (front end of input line and output gun head)

From the perspective of product principles, American standard AC charging stations are no different from national and European standards – they both serve as large electrical switches, conducting AC power from the grid to the onboard charger (OBC) in the vehicle, which then converts AC power to DC power to charge the power battery.

Although they are generally the same, there are still significant differences in many details compared to national and European standards. Otherwise, it would be too convenient to directly sell them in the United States without any modifications.

(1)

Before discussing the input lines of North American AC charging stations, let’s first introduce the voltage system of the AC power grid in the United States.

The power grid systems of most countries in the world are aligned with those of Europe (colonialism and war), that is, the normal household voltage is 220V~230Vac 50Hz, and the industrial three-phase voltage is 380~400Vac 50Hz. It is obvious that the voltage of industrial electricity is three times the root of the household voltage – the difference between line voltage and phase voltage.

The voltage system in the United States is unique, with the mainstream household voltage being 120V/240V 60Hz and the mainstream industrial voltage being 480V/277Vac 60Hz for industrial use. The voltage used for commercial or high-density residential purposes is 120V/208Vac 60Hz, while for some large heavy industries it is 347/600Vac 60Hz.

Are you also surprised why the voltage system in the United States is so chaotic.

The use of 110V voltage originated from Edison. It is Edison, who is well-known for inventing the light bulb. After multiple experiments and comparisons, he found that the light bulb had the highest luminous efficiency and longest service life when the voltage was 110V. So, in 1882, Edison officially introduced 110V DC electricity to the market at the Pearl Street Power Station, the first commercial DC power plant in the United States.

But we all know that direct current has a major drawback, which is severe heat loss during long-distance transmission, which wastes a lot of electrical energy. In order to avoid excessive energy loss during long-distance transmission, Nikola Tesla introduced his alternating current (AC) system. Although alternating current eventually defeated direct current, thousands of appliances and devices dedicated to 110V had already been installed in American households and factories at that time.

In order to facilitate a smooth transition to the era of alternating current, Tesla made a compromise: he also set the household voltage of alternating current at 110V. This not only protected the equipment investment of existing users, but also eliminated the public’s fear of high-voltage alternating current (which was widely believed to be more harmful to human health at that time).

Therefore, the adoption of 110V AC power in the United States is a product of accommodating 110V DC power.

With the advent of the electrical age, engineers gradually realized that compared to the later adoption of 220V/240V voltage in Europe, the 110V system in the United States suffered greater losses when transmitting high-power electricity and required thicker copper wires to avoid heating. But if we upgrade to 220Vac comprehensively, the cost is too high. The appliances, sockets, fuses, and even the entire city’s distribution network in millions of households across the United States are all designed according to 110V.

For this reason, electrical engineers in the United States have invented a highly intelligent “soil method” – Split phase technology.

Between the live wire and the neutral wire in the middle, a voltage of 110V/120V is formed, specifically designed for small household appliances such as mobile phones, televisions, and light bulbs (safe and not hot to the touch).

When two live wires are stacked together, they instantly turn into 220V/240V, specifically designed for “electric tigers” such as air conditioners, electric water heaters, and dryers (with high efficiency and low wire consumption).

Having understood the origins of 120Vac and 240Vac, the origin of 208Vac is also easy to comprehend. 208V is the line voltage of 120V (three times the root).

(II)

After understanding the voltage system in the United States, let’s now take a look at the input voltage of the American AC pile.

There are three types of voltage for ordinary AC charging stations used in the United States, namely 120V, 208V, and 240Vac. Basically, the promotion of pile companies will be based on the voltage bands they support, 110~120Vac or 200V~240Vac.

It should be noted that the charging station with 208V input is also single-phase input, not 16kw or 22kw as we understand it to be similar to the European three-phase five wire input. However, there are very few three-phase input charging stations in the United States that have been searched around the market but have not been found yet.

Among them, 110~120Vac is a regular plug connection that can support a maximum current input of 16A.

For AC charging stations with 200V~240Vac (208Vac or 240Vac) input, the front end of the input line can be in the form of a plug or a cable terminal. The “high voltage” socket with 240Vac input in the United States (consisting of four wires: two live wires, one neutral wire, and one ground wire) needs to be completed by a professional electrician.

By the way, the socket for connecting the input plug of the 240Vac AC charging station should comply with the requirements of NEMA14-50. Its maximum carrying current is 50A. According to the requirements of the American Electrical Installation Standard NFPA 70, the maximum current used by electrical appliances should not exceed 80% of the rated socket. So, the maximum current of a 240V input AC charging station with a plug can only reach 40A, with a power of 9.6kW.

(3)

After discussing the requirements for the input side of the American standard AC charging station, let’s skip the shell and look directly at the output side.

The output side of the communication charging station is very simple, just the gun holder and the gun cable that matches the gun holder.

If you browse the communication station website in the United States, you will find that any charging station will provide two types of gun sockets, namely the TYPE1 interface that meets SAE J1772 and the NACS interface that meets Tesla SAE J3400.

The specific structure and size details of the gun head and gun holder with two interfaces can be found in the corresponding standards.

Internally, there is no difference between Tesla’s NACS interface and SAE J 1772′s TYPE1 interface, both consisting of five wires – L/N/PE/CP/PP. Of course, Tesla’s design is very clever, with both DC and AC interfaces being the same set.

In terms of the North American communication pile market, the output charging interface is transitioning from the old-fashioned TYPE1 interface to the NACS interface, and more and more cars will choose to support Tesla interfaces in the future. Early AC charging stations equipped with TYPE1 interfaces were unable to charge the new NACS.

Of course, there’s no need to worry too much, there are plenty of adapters on the market that can help you.

Gun head adapters are strictly prohibited in the European standard IEC 61851-1:2017, but such clauses are not found in UL 2594 in the United States. It is not prohibited by law, just use it directly.

That’s all for the input and output sides of the American standard AC charging station. In the next article, we will share the design details of the “housing”.