EVSE “BATTERY CHARGER” for electric cars

By on June 13, 2019
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Let’s take a closer look to battery chargers for electric cars provided by manufacturers.

Those who have an electric car or at least a hybrid plug-in car (i.e. externally rechargeable) or whoever is in any way interested in the subject, will surely already know about them. They are also called Wall Boxes, EV Chargers, recharge stations or, in layman’s terms, “battery chargers”; it’s the EVSE, or Electric Vehicle Supply Equipment. The second E for equipment better explains the meaning of this mysterious EVSE, because it actually is a device that does a little bit of everything except for what you would expect it to do, which is managing the recharge current just like a normal battery charger; this happens because that actual process is carried out by the vehicle’s electronics.
With that said, what is the purpose of the EVSE, Electric Vehicle Supply Equipment? The question is actually legit. The answer is much richer and articulated then you would expect.

 

History

Since the first electric cars were born, we have been facing the issue of making the vehicle recharge safe. Basically, the same criteria and regulations in place for gas pumps would inevitably be going to be analogously applied to their electric counterparts.
So this is where “our apparatus” is tasked with carrying out a long list of control actions and tasks before allowing to initiate the recharge operation, in order to avoid possible risks involved in the process.

 

Safety first

As we know, water and electricity do not get along very well, however, the car must be usable even under the rain and the recharge operation is no exception. But the car is also being left outside a lot, subject to possible vandals or simply kids looking for troubles, therefore there are lock systems in place for the connector and the cable is fittingly robust. Furthermore, a car is a metal mass which, if not correctly grounded, might become a lethal trap for anyone touching it.
Then there is the issue of the electrical currents with which we are dealing, which can easily heat up when the contacts’ conductivity is less than optimal, therefore we need a protection mechanism to prevent overheating and/or fire; it is, therefore, necessary to monitor the connector’s temperature, both on the EVSE and on the vehicle side.
In conclusion, the system is designed to be safe. Very safe.

 

Cables

The cables are electrically oversized, which means their sections are thought for a continued an constant use at maximal nominal current, adding a safety margin, while the copper strands are always equipped with lugs to prevent the connector locking screws from damaging them. The cables itself are reinforced with the shield that makes them basically impossible to cut using common tools (knives, scissors etc.) and they are even capable of withstanding being run over by a truck’s wheel. Also, they are usually very well visible (they have a nice fluorescent colour that can be green, yellow or orange) to avoid running over them.







 

Standards for type 1 and type 2 connectors

Apart from the expected quality of the electric contact and the low hhm-resistance such connector must guarantee, the second challenge this component must face is waterproofing. Although there are already some industrial standards, the issue of a waterproof connector was maybe the first one the original producers of electric vehicles had to face.
After a certain amount of initial confusion where everyone was going their own way, we can say that, nowadays, there are substantially two types of standard connectors which are universally recognized, one is more commonplace in the US and Japan (endorsed by General Motors and Nissan) called Type 1 (Fig. 1), and another one, Type 2 (Fig. 2), is more common with European car manufacturers such as Renault, Audi and Volkswagen.

 

Fig. 1

 

The difference between the two types, at least in terms of shape and looks, is that the first one, the Type 1, SAE J1772, looks like a “space gun” and is equipped with a prominent locking mechanism which prevents it from accidentally falling out of its seat. It has a “trigger” activating a switch (which purpose we will see later) and it has three main pins, spaced at 120° between them, plus two other smaller ‘control’ pins. There is also an ‘extended’ version which has an additional pair of power pins, dedicated to high voltage DC charging (see level 3 below).

 

Fig. 2


The other one, Type 2, also called Mennekes, is also reminiscent of a gun, but it is bigger, also because it has two more power pins; in fact, this one can work either as monophase or three-phase. It only has one control pin and no locking ‘hook’, since the locking mechanism is composed of square holes and their counterparts in the fixed element (they are so weird that simply calling them male and female is not easy).

 

Fig. 3

 

Fig. 3 shows the pinout for Type 1 and Type 2 connectors with their versions.
There is also a third type of connector, called ChadeMo, born in Japan but not very common here in Italy, which is shown in Fig. 4.

 

Fig. 4

 







The four recharge levels

Besides the two different types of connectors, the IEC 62196 standards provide four types of recharging, each one having their own electric features and modes of protection and usage.
Level 1 is a 230 Vca monophase or 400 Vca three-phase (only with Type 2 connectors) direct passive connection, between the vehicle and the power line.
The electric protection is guaranteed only by a protection system in case of grounding malfunction, but it is now forbidden in almost any countries since the grounding is not always present.
Level 2 is a semi-active communication between the vehicle and the power line and provides protection against overcurrent and overheating.
Level 3 is an active connection between the vehicle and the recharge system, still, at 230 Vca monophase or 400 Vca three-phase (only with Type 2 connectors), it has the same features of motor 2 but it allows for a complete communication with the vehicle to regulate charge current. Note: the charging voltage is supplied to the vehicle only after the connector is inserted, thanks to an “ok” signal from the control system.
Finally, Level 4 is an active connection between the vehicle and the direct current 600 V recharge system. Here, the power is straightened for the charging by the recharge system, before being supplied to the vehicle. It is, therefore, more complex and costly compared to previous systems. It guarantees shorter recharge times and it is the standard for electric-only vehicles with bigger batteries such as Teslas where we need a big amount of power for recharging in short times.
In March 2011, ACEA, on the half of the main European car manufacturers, published a document where they recommended Type 2 Mode 3 as a common standard for the European Union to be adopted by 2017. Therefore, at the moment, the Type 2 connector, used under Mode 3 or 4 is to be considered the currently applicable standard for our country.

 

Main functions 

As seen before, our EVSE must do a series of things for safety control purposes, before physically providing power, whether monophase or three-phase, alternating or straightened direct power, to the vehicle itself, which will take care of using it for recharging in a completely autonomous manner.
First of all, there is a grounding check. To do that, it will naturally have to check if there is no current flowing through the ground wire, as well as no current difference between phase and neutral (or between the three phases in case of three-phase connection), taking advantage of the same principle of differential switches, commonly known as circuit breakers.
After this check, the EVSE will check to make sure the power grid’s specs are valid and within the defined ranges, and will possibly notify with a related error. Finally, it checks if the connection with the car is activated through the feedback pin provided on the connector itself. If everything is good to go, the connector is inserted and the car responds that it is ready to start charging, the EVSE will initiate the charging status by activating a contactor which will bring the power grid voltage to the connector itself and then to the vehicle.
During the recharge, the vehicle will keep the “OK” signal on the control pins as long as everything is fine. In case of overheating or other anomalies, the vehicle will interrupt the recharge and change its status, which will make the EVSE cut power to the connector. As soon as the vehicle detects it, it unlocks the connector lock so that it may be removed from the outlet on the car. The system is designed to always prevent sparks on the connectors during insertion and removal so that everything happens under the controlled absence of power.
Other vehicles are also capable to signal the EVSE a special “ventilation needed” status that the EVSE can signal using an alarm light and/or activating an auxiliary switch which, for instance, could activate the fans if the environment is confined such is the case with a garage. This happens because the chemicals inside the batteries, under extreme use conditions, may release hydrogen, which is very dangerous.
the last function we mention is the measurement of temperatures on the connectors: in wall-mounted EVSEs, or Wallboxes, there is a temperature sensor on the EVSE’s connector plug, while the car’s electronics takes care of monitoring it on the vehicle site. In some portable EVSEs, those where the wires come out directly from the device (one going to the car connector and the other one is the EVSE power, terminating with a plug for a standard home power outlet) we can sometimes find a sensor built in the plug itself (an example is shown in Fig. 5).

 

Fig. 5


This happens because the plug can heat up easily, since, 16 Amax plugs like the Shuko type are designed for noncontinuous 16 Amax and therefore not fit to use. For instance, Volkswagen provides an EVSE of this type, with a Shuko plug, however, it is limited to 10 Amax, although the GTE can be charged up to 16 Amax.

 

Recharge current adjustment

We find the titular characteristic right between the EVSE’s essential features and its options, since the vehicle itself already offers, inside its settings menu, the possibility to set the maximum current at which to recharge the vehicle. Therefore, having an EVSE that allows setting a charge current limit is not mandatory, but can also be very useful. For this reason, our EVSE would have to intervene to agree upon that value with the vehicle itself, and the chosen value will be the lower of the two. If, for instance, we set the max current to 12 A on the EVSE but we set it to 8 A max on the vehicle, we will see that our EVSE outputs no more than the 8 A we set previously. Vice versa, if we were to set 6 A max on the EVSE, the maximum current absorbed by our vehicle will drop to 6 A, although the maximum limit set on the vehicle is 8 A. This communication takes place using a PWM duty cycle modulation of a 1 kHz signal emitted on the control pins, which “tells” the car to current limit at which to start recharging. Fig. 6 shows a table with the relationship between the duty cycle and recharge current.

 

Fig. 6

 

Other useful features

Those who own an electric vehicle or a Plug-in Hybrid (therefore rechargeable via EVSE) know that it is very useful to be able to know the recharge current, and therefore the recharge power, for several reasons. First, in order to avoid a blackout in our house, especially if there are other domestic loads connected, but also to know how long we will have to wait for a complete recharge, e.g. if we are recharging from a public station.
Once we know the battery’s nominal capacity, for instance, 8.7 kWh for the Golf GTE, we subtract the residual autonomy that should always be left as residual, if we set the car for never dropping below 20%, we get around 7.0 kWh.
Well, this is the energy we have to introduce to recharge the electric “tank” of the car, therefore if we are charging at 10 A, i.e. 2.2 kW power (220 V x 10 A) we know that we will introduce around 2.2 kWh each hour. In 7/2.2 = 3.2h c.a, our recharge will be complete.
On the other hand, if we were to recharge at maximum current/power allowed by the car, i.e. 16 A, we would complete the recharge in 7:220:16 = 2 h.
The car in our example is a plug-in hybrid, therefore the battery is relatively small (the manufacturer states around 45 km autonomy in electric-only mode) but there are pure electric vehicles such as the Nissan Leaf, Renault Zoe, BMW i3, Hyundai Ioniq, Kia Niero etc. with batteries well over 40 kWh; not to mention the 70 kWh and more of some Tesla models.
In order to recharge those batteries, we need a lot of power, especially if we need to complete recharge in reasonable times and setting the right recharge current can be very important. That’s why some EVSE models allow measuring the effective kWh introduced with every recharge in the electric tank known as the battery, also to monitor a possible degrade of the battery itself, which is shown as loss of capacity (we can see the capacity decreasing). Besides, those versions equipped with Wi-Fi connection are often combined with a software app allowing to easily make these calculations, translating a certain recharge time in kilometres of autonomy applied to a partially charged battery and can also tell us how many minutes of recharge we would need to drive for a certain amount of kilometres.

 

Advanced EVSE

In Germany, where photovoltaic systems are widespread, we can easily find measurement devices allowing to measure the energy produced, the energy consumed and the energy fed to the power grid. These are current sensors to apply to the systems wires measuring the current and calculating the related consumptions, and then transmitting them over the radio (at 433 MHz frequency) to a control unit connected via ethernet to a server which registers the data and which apps are based on, in order to show consumption graphics later. An example is shown in Fig. 7.
some EVSEs have a similar system to integrate consumption data for recharging the car with the data related to home consumption in order to allow the EVSE to set the car recharge power which is dynamically always equal to the best available value obtained as the difference between output power from the FV (or, when there is no FV self-production, the maximum power obtainable by the meter) and the power absorbed by the domestic loads, optimizing the recharge and avoiding annoying blackouts.
On an advanced EVSE, it is also very useful to have a calendar with the possibility to set a scheduled starting hour range for recharging because, although many vehicles already have similar features, they only allow to set the starting hour, not the recharging start hour (time automatically added by the vehicle) which is always variable, because it depends on how much battery capacity is left since the last use.
In the end, this doesn’t allow to start the program recharge at a specific time using the car’s timer, which is instead quick and easy to do from the EVSE.

 

Fig. 7

 

Prices and speculation

If you ask any car dealer, they will all mention around €1500 as the price for a recharge column or Wall Box, as they love to call them; the amount does not include installation. The more luxurious brands can go as high as €3000, but we are still talking about EVSes, often with identical features. Sure, if you are spending 30k, 40k or maybe €50,000 for an electric car, maybe €2000 for installing an EVSE will not be a big deal, but if you have read this far, you probably already figured that the hardware value of an EVSE is hardly 1/10 of those figures.
All this speculation paved the way for the makers’ smarts and launched a series of EVSE projects that are more or less open-source in nature, such as those you can find on the web at the following addresses:

http://www.aprs.org/charging-DIY.html;

https://www.openevse.com/;

http://www.instructables.com/id/DIY-J1772-EVSE/

 

And many, many others you can find with a Google search, for instance, using the keyword “EVSE”.



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About Boris Landoni

Boris Landoni is the technical manager of Open-Electronics.org. Skilled in the GSM field, embraces the Open Source philosophy and its projects are available to the community.

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