Destroys magnetism DC batteries

Electric car charging

Lexicon> Letter L> Charging electric cars

Definition: the charging of the batteries of electric cars, which can be done by cable (conductive) or contactless (inductive)

Alternative terms: charging electric cars, battery charging

English: charging of electric vehicles

Author: Dr. Rüdiger Paschotta

How to quote; suggest additional literature

Original creation: 03.08.2020; last change: 04/25/2021


Many websites explain such relationships, but important details are often missing or even incorrect statements are made. In addition, there is often a lack of intelligibility. Here you have an article that competently gets to the bottom of things and explains them clearly.

An electric car usually draws the electrical energy for the drive electric motors and other loads (e.g. heating and air conditioning) from a rechargeable battery (an accumulator). This battery then needs to be charged regularly. In this context there are a number of partly non-trivial relationships that are explained here.

In fact, some things are quite surprising. An example: How can it be that a car that has a charging power of 70 kW at a fast charging station can only draw 4.6 kW from a wallbox with a nominal power of 22 kW? To do this, you have to understand some technical relationships, also in order to avoid the unfortunately often occurring deceptions. We start with the simpler aspects that are easy to understand even for laypeople.

The focus of the article is on charging with energy from the power grid. If solar energy from your own photovoltaic system is used, it usually does not change the charging technology at all, because the mains voltage is usually used as an intermediate level instead of using direct current to charge the battery. The only thing that may then be appropriate is to influence the charging times appropriately in order to be able to use as much solar power as possible for self-consumption.

We mainly deal with the conductive charging that has almost always been used up to now, i.e. via a charging cable, but also inductive (contactless) charging. In residential buildings, charging with a direct connection to a normal socket or via a compact device that is mounted on a wall in the garage, for example, is common (Wallbox). There are also public charging stations (mostly charging stations, also known as charging stations or e-charging stations), and sometimes also fast charging stations with a high charging capacity. (Charging with more than 22 kW counts as fast charging.) In addition, there are charging stations, for example, in companies for their own vehicle fleet and for their employees.

We will only briefly address the concept of replaceable batteries that has not yet been put into practice in cars (unlike two-wheelers) - i.e. the replacement of a discharged vehicle battery with another that has been charged in a stationary manner. In principle, this could bring the full range within a few minutes, but in practice it is not that easy to implement.

Charging time depending on the charging power

An important aspect is the time it takes to charge a battery. First of all, this is relevant for the vehicle user - less spent the night while charging at home, more when charging stops, e.g. B. at motorway service stations. Fast charging is also more important for the operators of charging stations: the faster it is, the more vehicles can be processed per day and the sooner the installation costs can be amortized. In this respect, slightly higher installation costs can also be affordable. Of course, it must be prevented that individual trolleys block the charging stations for much longer than necessary for charging.

The charging time mainly depends on two things: the amount of energy required and the charging power. However, a certain percentage of energy losses, which occur in the charging station, in the charging cable and in the vehicle (especially in the battery), is still reduced from the charging power. In more favorable cases, these losses are around 10%; unfortunately they are even higher than 20% for some vehicles, and the manufacturers usually say little or nothing at all. We will come back to the energy efficiency, which is of course reduced by the charging losses, below.

If the charging losses are known at all: Does the charging power relate to the power drawn from the network or to what ends up in the battery?

For the calculations in the following, we assume that the specified charging power is the power drawn from the grid and that less actually ends up in the battery.

If the battery is completely discharged at the beginning (which should rarely happen in practice), the amount of energy required corresponds to the total usable capacity of the battery, which is specified by the manufacturer in kilowatt hours (kWh). If the battery was only partially discharged, less energy is required for charging.

The charging power (like an energetic power in general) means the amount of energy supplied per unit of time. The usual unit here is the kilowatt (kW = 1000 watt). In most cases, the charging power is limited either by the charging station or by the technology in the vehicle, in some cases also by the load capacity of the charging cable used. Below is an explanation of which charging capacities are possible under different circumstances.

The charging time is then simply the amount of energy required divided by the charging power, if the latter remains constant during charging. You can then simply use the following calculator:

In practice, however, it is often the case with electric cars that the full charging power is only available up to a state of charge of e.g. B. 80% can be used; after that, the charging power must be reduced considerably in order to protect the battery. This is especially true when using fast charging stations, but usually not when charging at a normal socket or a small wallbox, where the charging power is low anyway.

Two numerical examples:

  • Charge of 30 kWh from a household socket with only 2 kW and 15% loss: This takes 17.6 hours; without energy losses (or if 2 kW meant the effective charging power) it would be 15 hours.
  • Charging a 50 kWh battery from 10% to 80% with 20 kW with 15% loss: The charging time is 0.70 · 50 kWh / (0.85 · 20 kW) = 2.06 hours.

Charging at low or high temperatures

Lithium batteries, such as those normally used in electric vehicles, work best at temperatures of around 20-25 ° C. If, on the other hand, in winter, B. reach 0 ° C or even less, they are much less resilient. The charging electronics take this into account by massively reducing the charging power, which leads to correspondingly longer charging times. For vehicles that are outdoors in winter, this can be a problem. After all, it is helpful that the charging itself leads to a certain warming of the battery system. Charging immediately after arrival can also be helpful because the batteries are slightly warmed up while driving.

Even high temperatures of z. B. 30 ° C or more are unfavorable for the batteries. Even then, the charging power should be reduced, although the heating during charging naturally has a negative effect here.

When unloading by driving at full throttle, of course, significantly higher performance occurs - but usually only for a short time. However, it is advisable to hold back here in extreme temperature conditions in order to save the battery.

Charged energy and range

Another relatively simple relationship exists between the amount of energy charged and the range of the vehicle, or the increase in range as a result of a certain charge. This depends on how economical the vehicle is, i. H. how much energy it needs to drive 100 km.

Of course, the entered amount of charged energy and the consumption should either both include the charging losses or both should not.

In practice, the consumption values ​​will vary significantly depending on the driving style and external circumstances. Above all, heating or cooling the vehicle significantly increases power consumption, especially in city traffic (where one is on the road for 100 km significantly longer). That is why you will never be able to precisely predict consumption on the coming route. At least a reasonable estimate is possible. You should by no means blindly trust the manufacturer's consumption information; The values ​​based on norms such as NEDC or WLTP are also usually significantly over-optimistic compared to practice (which is especially true for NEDC values). The specification of a range as “up to ... km” naturally shows that one should be careful with it.

Charging costs at home and at public charging stations

At home

The electricity costs for operating the electric car are easy to determine if the amount of electricity consumed is known (or can be estimated based on the distance traveled and the specific consumption) and if the price per kilowatt hour is known.

A numerical example:

  • If a small (relatively economical) car is driven 10 000 km per year with a consumption of 15 kWh per 100 km, this means a consumption of 1500 kWh per year. With a household electricity tariff of 30 ct / kWh, this means costs of 450 € per year.
  • For comparison, a petrol car with a consumption of 5 l per 100 km per year would use 500 liters of petrol. At a petrol price of 1.40 € / l (as of January 2020) this would result in costs of 900 € per year - i.e. double the electricity costs.

It is therefore easy to cope with the fact that the household's annual electricity bill has increased significantly as a result of the introduction of electric cars. (The comparison with the other electricity costs is of course not relevant.)

Please note again that official consumption values ​​are not necessarily achievable in practice.

It is also important to note that the display of the power consumption in the car does not normally include the charging losses, which also depend on the respective charging technology. So you would underestimate the costs a bit if you calculated the operating costs on this basis.

If additional infrastructure has to be installed at home (see below), the resulting costs can also be attributed to the z. B. be transferred within a few years driven kilometers. Of course, this can be a significant cost factor. However, setting up a charging point can also be viewed as an increase in the value of the property, and anyway these fixed costs are usually low compared to purchasing the vehicle.

Public charging stations

The costs at public charging stations are very different:

Offering free charging can be a useful measure to attract new customers to various businesses. The charging power is usually rather low.
  • A number of charging stations, for example in supermarkets, are free - intended to attract additional customers. For example, if 5 kW can be charged for half an hour while shopping, this is 2.5 kWh of energy, for which a private household would pay approx. € 0.75; for a commercial enterprise it is usually significantly less. At the same time, the operator saves himself the expense of a billing system. It only becomes annoying for the provider when people take advantage of this excessively - for example, charging without actually shopping there, or charging for a much longer period of time, which also blocks valuable charging points and possibly annoys other customers who no longer have a free charging point Find.
Unfortunately, the large variety of sometimes complicated tariff models makes cost comparisons quite difficult.
  • When billing occurs, it can be based on very different pricing systems, which can create confusion. For example, a simple kWh price like at home (possibly with a much higher tariff), a time-dependent tariff (accurate to the minute or, for example, for every half hour or part thereof) or a flat rate per refueling process regardless of the charging capacity used (which can be quite expensive, for example if a vehicle can only charge single-phase with low power). Often there is also an annual or monthly basic fee in connection with the registration for the respective provider, in other cases only a one-time activation fee, or a basic fee per charging process. A regular basic fee is of course only worthwhile if it is used frequently enough. Basically, comparing costs is often difficult because various details have to be taken into account, including the unpredictable number of charging processes per year, which can also be limited by the availability of the corresponding charging station.

In Germany, for example, billing based on the amount of energy consumed requires that the charging stations are equipped with calibration-compliant electricity meters. So far (as of 08/2020) there are no calibration-compliant meters for DC fast charging stations, which is why a special regulation applies. Often a flat rate is charged per charging process, which is of course less favorable for users of small cars with small batteries (as well as for customers who arrive with only partially discharged batteries).

It should be noted that the providers not only have to recoup their electricity costs, but also have to amortize the infrastructure that has been built and cover various additional costs and risks - such as repairs after defects (possibly caused by jostling and hit-and-run).

For example, car manufacturers who offer their special stations as an important additional benefit for the vehicles they sell and therefore do not necessarily have to make a profit with the operation of the stations can calculate more generously.

Operation with green electricity

An electric car can only drive really cleanly with real green electricity.

Anyone who buys an electric car should usually be concerned with driving as environmentally friendly as possible. A decisive factor for this is of course that green electricity is used for the operation. Otherwise the climate-damaging CO will arise in particular2Emissions - not in the car, but in the power plants that generate the electricity for charging the batteries. A numerical example: If a relatively economical vehicle consumes 15 kWh per 100 km and is charged with electricity from a lignite power plant with emissions of 1100 g / kWh, this corresponds to 16.5 kg of CO2 per 100 km or 165 g / km. That would even be considerably worse than a gasoline-powered vehicle of the same size. If there is at least a significant proportion of coal electricity in the electricity mix used, you might be a little better than a gasoline car, but not very much.

If a provider talks about green electricity without being able to show a well-known certificate (electricity label) for it, there is likely to be a number slide without any ecological added value!

Only with real green electricity does the electric car become really environmentally friendly. It must be emphasized here that sham packages that are often offered serve at most to calm one's conscience, but without actually offering the expected ecological quality. If, for example, an electricity provider announces that he only supplies electricity from hydropower to private customers or to his charging stations, it can happen that he sells “dirty electricity” to industrial customers at the same time - which can then mean that every additional kilowatt hour consumed by the private customer is an additional dirty one Kilowatt-hour caused. Unfortunately, such consumer deception is legal. As a rule, it can only be avoided by buying electricity with a recognized green electricity certificate (green electricity label).

When charging at home, everything is already done if the household is generally supplied with green electricity. On the other hand, when charging outside the home, you have to keep checking which power quality is being used. Many charging stations are operated with electricity of an undisclosed quality (or with green electricity without a label), which means that a considerable proportion of “dirty electricity” can be expected. Some providers, on the other hand, have a recognized certificate, and then one can assume almost emission-free driving (apart from the gray energy for the manufacture of the vehicle).

Finding charging stations

A very practical help in finding charging stations, especially while driving, is that electric cars are often equipped with navigation systems that have the relevant data. Ideally, it will also show whether you get green electricity, which charging technologies (see below) and which charging services these stations offer and whether they are actually available at the relevant time - although it is of course not possible to predict whether all charging points will be occupied later. It is also important to update the data regularly, especially because more stations are added all the time, but also because some of them can temporarily fail due to defects.

Current data can also be found on various websites on the Internet, which can be particularly useful for travel planning. Unfortunately, the information is often not very clear, for example because there is no comprehensible legend for the symbols used.

When planning your trip, it is advisable not to rely on a specific charging station, but to ensure that another can be found not too far away.

Charging technologies

In principle, you can not use the vehicle battery z. B. simply connect to the power supply, because you need a DC voltage of the correct amount for them and also set the charging current appropriately. In addition, various security aspects must be taken into account. That's why you always need some kind of charger, either in the vehicle or in a charging station - usually even some electronics on both sides. Some very different technical approaches have been developed, with specific advantages and disadvantages, which are explained below. All of them occur in practice, and as a driver you should at least understand their basic characteristics.

Single-phase alternating current charging

For historical reasons, our power grids work practically all with alternating current or three-phase current in the form of three-phase alternating current. For both one can find the designation AC = alternating current. Since all batteries must be charged with direct current, a rectifier is definitely required. In addition, there is the necessary adjustment of the electrical voltage to the battery voltage and the regulation of the charging current. Where exactly this technology is located - in the vehicle or in a charging station - depends on the approach chosen.

You can get by without any special charging infrastructure if you simply charge an electric car at a normal socket outlet in or on the house. The rectification and charging control then usually takes place in the charger, which is integrated in the electric car.

Unfortunately, single-phase charging has the following disadvantages:

Household sockets are not necessarily suitable for the constant load in the store - especially not if they are old! If in doubt, an electrician must check it.
  • The load capacity of sockets is initially limited by the respective fuse, which normally allows a current of either 16 A or only 10 A. In addition, especially with older installations, it is questionable whether the lines from the meter box to the socket (including junction boxes, etc.) are suitable for a constant load at this level; In principle, household sockets are not intended for a permanent load in the amount of the secured value. Especially when electrical contacts become poor due to corrosion or unforeseen mechanical stress, i.e. have increased electrical resistance, it becomes too hot in the long term if there is a strong flow of current; it can even create a fire hazard. If in doubt, an electrician should check the cables before use and replace them if necessary, and of course you should be very careful if there are any signs of cable overload (such as a characteristic odor). As a precaution, the chargers of many manufacturers limit the charging current to approx. 10 to 12 A. (Note that the heat development increases with the square of the current, which is why the limitation to 10 A instead of 15 A, for example, already massively reduces the load on the line .)
Only quite limited charging capacities are possible.
  • Due to the use of only one phase (single-phase alternating current) and the moderate mains voltage of 230 V (e.g. in Germany), the charging power is relatively low - e.g. B. 2.3 kW at 10 A amperage. This results in correspondingly long charging times of often well over 10 hours. That may be enough for many drivers, but not or not always for others.
  • Of course, there is no question of charging two or more electric cars from nearby sockets at the same time, unless they have separate lines and fuses.
  • A so-called unbalanced load occurs, i. H. an asymmetrical load on the three phases - but within the permissible range, so that this is not a real problem here.
  • Surprisingly, the charging losses with this method can even be a few percentage points higher than with faster charging, since the charging electronics often have a certain basic consumption, which is correspondingly more significant with longer charging times.
  • The handling is a little less practical than on a charging station with a cable, as you first have to remove the charging cable with charger from the car and plug it in on both sides.

Incidentally, you should avoid using any accessories such as multiple sockets, travel adapters, extension cables or even cable drums, because they introduce various additional risks of overloading components. In particular, the use of cable drums in the largely wound-up state is problematic because they can get quite hot over time.

Three-phase charging

Many charging stations offer three-phase current, i.e. three different alternating current phases, the electrical oscillations of which are each shifted against each other by a third of a period. If all three can be used, the result is three times the charging power with the same current strength, and any unbalanced load can be avoided.

To connect the car, you don't usually just need a conventional three-phase plug (the red CEE plug), but a charging station with a different plug connection. Such three-phase charging stations provide all three phases. In Europe, type 2 connectors, also known as Mennekes plugs, are almost always used for this. They offer the three phases, neutral conductor and protective conductor, as well as two control contacts called PP and CP (see below, charging mode 3). Figure 1 shows such a vehicle coupling. (It's not a plug; the prongs of a plug are in the vehicle, and what you hold in your hand is a coupling.)

The charging cable between the station and the vehicle is in some cases firmly attached to the station, but the vehicle owner often needs his own cable that must be carried with him at all times - actually a nonsensical solution, since such a large number of relatively seldom used cables are in operation and the handling is more complex becomes. In addition, some of the cables supplied with the cars limit the charging power below the level possible from the station. On the other hand, it can be beneficial if a charging station offers boxes for a number of different charging systems; Having a permanently attached cable for each of these would be a space-consuming and confusing solution.

Charging at the three-phase connection does not necessarily mean three-phase charging!

Another complication is that there are many vehicles whose internal charger only works in one phase, i.e. can only use one of the three phases. Accordingly, only a third of the capacity of the charging station can be used. It can be even less if the vehicle cannot use the full charging current, the charging cable used is too weak or if the charging current has to be limited in order to keep the unbalanced load within the permitted limits. In Germany, this limit is currently 20 A, corresponding to 4.6 kW, and will probably only be 16 A / 3.7 kW in the future. (Other European countries usually already have lower borders than Germany.)

A total of 4.6 kW charging power when using a 20 kW charger - although about 70 kW are possible at fast charging stations! Disappointments are inevitable.

The Hyundai Ioniq Elektro is a typical example of the latter situation. So far (as of August 2020), like many other electric cars, it has only been equipped with a single-phase charger, which can draw up to 28.5 A. If the charging station allows this amperage, you get a charging power of just under 6.6 kW. If all three phases were used, it would be almost 20 kW, and such an indication will then also be found on the charging station. Presumably it often happens that a car buyer has such a charging station set up on the assumption that it would then charge the car with approx. 20 kW, which of course leads to disappointment. The same applies to public AC charging stations. Often the permitted effective current is even limited to 20 A - namely by the charging cable supplied with the car and / or by the limited unbalanced load - with which one only achieves 4.6 kW. Unfortunately, it is precisely this misunderstanding that is (intentionally?) Encouraged in various texts on the Internet (e.g. from car dealers). Often the information is not objectively incorrect, but “only” clearly misleading - for example, if a charger is expressly stated as being suitable for a particular car, its nominal power is stated and thus falsely suggests that the car could then be charged with this power. In case of doubt, the buyer should have a guarantee that the specified performance can actually be used or that the maximum charging time is achieved with it.

However, there is also a technical solution for this: There are devices that draw power evenly from the three phases of the power grid (i.e. without unbalanced load) and output it via a single phase. In this way, a higher charging power can be achieved even with single-phase charging - but unfortunately only with an additional device and a stronger charging cable, and still much less than with real three-phase charging.

DC charging

As an alternative, many vehicles offer the option of charging with direct current (DC = direct current). In this case, the rectifier is not located in the vehicle, but in the charging station, and the power is supplied via two lines in the charging cable, which carry oppositely equal voltages to earth. The entire charger in the vehicle, including the rectifier in the vehicle, is bypassed, and much higher charging capacities are often possible. The current flows directly into the battery. The charging current is controlled here by the charging station, Not of the electronics in the car; this only informs the charging station of the relevant parameters (state of charge, maximum charging current, etc.).

The CHAdeMO system was initially developed in Japan for the connection. This is only suitable for DC charging, not for AC charging. In Europe, therefore, a different approach was followed, that of CCS (Combined charging system) led. Type 2 combo connectors are used here, which can be used in two different ways (see Figure 2):

  • Where you only have the option of AC charging from the charging station, you can connect the usual type 2 charging cable to the combo plug.
  • DC charging stations are equipped with a vehicle coupling that uses the entire combo plug. This contains two conductors for the transmission of direct current, which are located next to the AC conductors and would be left free by a standard type 2 connector. The signal lines of the type 2 part are also used for DC charging.

Since this approach has been declared mandatory at European level, most new electric vehicles have been equipped with it for a number of years. This means that users have a wider choice of charging stations.

Fast charging stations deliver high currents and sometimes also high voltages.

The concept of DC charging is mainly used for fast charging stations, which are available, for example, at motorway service stations. These facilities must have a strong connection to the public power grid, usually at the medium-voltage level. An electrical voltage of z. B. 500 V - but not about 500 V to earth, but ± 250 V. The currents can sometimes be quite high, e.g. B. 100 A for an output of 500 V · 100 A = 50 kW, but sometimes also 200 A (CCS 1) or even 400 A (HPC) - later probably even more for outputs of hundreds of kilowatts. For this, of course, you need correspondingly large cable cross-sections, i.e. relatively heavy and inflexible cables that you would not find in a household appliance. That is why there are also developments for the use of a higher voltage of 800 V (i.e. ± 400 V), for example at Porsche (“Porsche Turbo Charging”). Of course, the battery voltage has to be that high if you don't want to install a high-performance DC / DC voltage converter in the vehicle.

Up to now, direct current charging (DC charging) has hardly been common in residential buildings. There are already DC wall boxes that allow significantly faster charging than the more common AC devices, but with outputs in the region of 20 to 50 kW. Even then, the costs have so far been massively higher than for the AC devices with correspondingly lower performance. However, it is to be expected that this will change soon so that this future-proof solution can prevail.

A disadvantage of the CCS approach is that, with a view to the potential of DC charging, optimizing AC charging is mostly neglected by vehicle manufacturers - with the result that one at home, where a DC charging station has often been too expensive up to now, is neglected , can only charge single-phase with correspondingly low power (see above). As already mentioned, this problem should only exist temporarily until cheaper DC chargers are also available for private homes. Basically, it makes more sense to install the expensive electronics in a stationary manner and not in all vehicles, especially if a station can be used by several vehicles.

Should AC charging be abandoned in the future, one would of course have to think about a new standard that would make the technology for the AC part (including the additional conductors in the charging cables) unnecessary.

Inductive charging

In some situations it is advantageous if an electrical connection does not have to be created manually by plugging in a cable for charging. For this there is the technology of inductive (contactless) charging, i. H. with inductive energy transfer.

The basic principle is that of a transformer. For example, the primary coil of this transformer, which generates an alternating magnetic field, is housed in the floor above which a vehicle can be parked. This induces an electrical voltage in a second coil inside the vehicle and thus effectively transfers energy that can be used for charging. For this, the vehicle should of course be parked precisely in the right place.

When operating with the normal network frequency, this method would clearly not be sufficient for the transmission of sufficiently high power with reasonably acceptable energy losses. However, there is the possibility of operating such a device at much higher frequencies, so that one can manage with much smaller coils and at the same time achieve much better energy efficiency. However, the efficiency is still several percentage points lower than with a simple and correspondingly cheaper cable connection. Thus, the effective power consumption of the car increases by z. B. another 15%. In addition, the achievable charging power has so far been limited to a good 20 kW (as of 2020).

The very limited distribution of inductive charging devices is also due to the fact that it has not yet been possible to agree on a specific system. Corresponding standardization is still pending. That is why serial installation in electric cars is not realistic today, and subsequent installation is not anyway because of the significantly higher costs.

By the way, inductive charging is a catastrophe for electrosmog phobics. At least in the immediate vicinity of the vehicle, there are strong alternating magnetic fields that put those from various other sources in the shade. The acceptance that this calls into question could be another obstacle to the spread of this technology. After all, the range of these magnetic fields is quite limited; the field strength drops much faster with increasing distance than, for example, with mobile radio transmitters.

Inductive charging devices will probably initially come into consideration for certain special applications, for example for quick intermediate charging of city buses during short stops, where a cable connection would certainly not be practical. Something similar is conceivable for autonomous small vehicles in factory halls.

Cooling the battery

Active cooling of the battery system is necessary for particularly high charging capacities. Many vehicles have such a facility built in and it is automatically activated when necessary. In the case of high-performance charging stations, even the charging cables are actively cooled.

Incidentally, the energy losses are significantly higher when charging very quickly - not only because of the additional energy required for cooling, but also because of the somewhat higher charging voltage that then tends to be necessary.

Energy efficiency

Since it involves considerable amounts of energy, an energy-efficient solution is of course desirable. For this purpose, the charging losses mentioned above in particular must be minimized. Unfortunately, it is often not easy to determine, for example, the energy losses caused by different charging stations (ideally before buying, of course), as the information available is often sparse and unclear. For example, it is often not clear to which charging situation (e.g. charging power) such information relates and what the losses would be in other situations.

Fortunately, the percentages of energy losses in charging stations and with chargers integrated in the vehicle are usually not dramatic.This is also due to the fact that increased energy losses would also generate a corresponding amount of heat that accumulates in the device and would have to be removed by a corresponding cooling device. The manufacturer often saves money by designing the electronics as efficiently as possible so that they do not have to invest in cooling. This applies in particular to more powerful chargers, where correspondingly larger amounts of waste heat are involved. The greater part of the energy losses should then occur in the vehicle battery; with typical lithium-ion batteries, these losses are in the order of magnitude of 10%. Good chargers can usually have losses of less than 2%. At the same time, you shouldn't have any significant standby consumption.

The highest energy efficiency should usually be achieved with medium charging capacities - around 20 kW. However, neither the fast charge nor the slow charge at the socket should bring dramatically worse values. Therefore, energy efficiency is rarely an important decision criterion for the choice of charging technology, except for inductive charging.

Safety devices

In contrast to small household appliances, various safety aspects must be taken into account when transmitting electrical power as high as that required to charge vehicle batteries:

  • It must always be ensured that the vehicle body remains electrically at ground potential, otherwise the matter could be dangerous for people standing next to the vehicle. Electronics must therefore check whether the grounding actually works.
  • So-called residual currents, which are expressed as imbalances between the currents in the charging cable lines, must be reliably monitored with a residual current circuit breaker in order to interrupt charging if necessary. Ultimately, fault currents could result in a person being electrified via a charging cable with damaged insulation - even if harmless causes are just as possible. (Residual current circuit breakers are also common in other areas of the household, especially in bathrooms.)
  • Of course, destruction of the battery due to charging errors must be avoided at all costs. If the vehicle battery and, as a result, the entire vehicle and possibly even more, went up in flames, the damage would be immense. Therefore, a whole series of switch-off criteria must be carefully implemented.
  • Appropriate protection against faults caused by overvoltages from the network, for example lightning strikes, is also very advisable in order to avoid costly failures of the charging infrastructure.

Charging modes

For those interested in technology: A distinction is made between several standardized charging modes (charging modes) according to DIN EN 61851-1 (VDE 0122-1):

  • Charging mode 1: This is only used for two-wheelers such as e-bikes. The vehicle is connected to a normal earthed household socket via a cable. The charger is usually located in the vehicle.
  • Charging mode 2: This requires a relatively small control and protection device, which is usually a small box through which the charging cable runs, as well as a compact charger in the car. This is also about AC charging, single- or three-phase. This method is used for cars when charging is carried out via a normal socket that does not need to have any special safety devices. In turn, a protective contact socket is usually used, more rarely a CEE socket.
  • Charging mode 3 (so far dominating for cars): Here, too, AC charging is implemented in one or three phases, but with a z. B. in the building or outdoors permanently installed charging station (e.g. a wallbox) that contains the safety devices and communicates with the electronics in the vehicle in a standardized way via the charging cable. Communication takes place via additional control lines, which are referred to as PP and CP in the type 2 systems used in Europe. First of all, the vehicle reports that it is available and, if necessary, ready to charge. Conversely, the charging station announces how high a charging current it can provide. In addition, the maximum charging current that the charging cable can transmit is taken into account; For this purpose, such cables are provided with a resistance coding that the electronics can query. The charge is then controlled via the charger in the vehicle. Charging capacities of up to 43 kW have been possible so far.
  • Charging mode 4: This is DC charging (direct current charging) as explained above. Here the charging station takes over the entire charge control - based of course on the information about the battery (state of charge, maximum charge current) that it has received from the vehicle. Very high charging capacities are possible.

Instead of charging mode 3 (for example) one often speaks of charging mode 3 or mode 3. The number of the charging mode has little to do with the type of plug connection; For example, type 2 plugs are often used for charging mode 3.

Planning of charging installations

Good planning is particularly advisable when a combination of several charging devices is required. This applies not only to the selection of the charging technology (e.g. AC or DC), but also to a number of other details, e.g. relating to load management, consumption recording, billing and user authentication, protection of the charging equipment (e.g. against bumping into the car and the weather) etc. It is of course important to avoid expensive subsequent changes or retrofitting by installing a future-proof solution right away - possibly also taking into account the possibly soon increasing demand for additional vehicles.

If certain technologies (such as the use of Internet connections for communication) are currently not in use, suitable precautions should nevertheless be taken to make retrofitting as simple and inexpensive as possible. For example, conduits for additional network cables can be very helpful.

Charging power and battery life

Real quick charges can affect the life of the battery.

Basically, a high charging power can reduce the service life of the battery, on the one hand through the associated heating and on the other hand through electrochemical processes in the battery, which then go hand in hand with the somewhat increased charging voltage. The problem of warming is countered by actively cooling the batteries, which of course can be more or less effective depending on the vehicle. The electrochemical problem is alleviated to a large extent by the fact that the charging power z. B. is significantly reduced from a charge level of 80%, because the battery is particularly sensitive in this situation. Nevertheless, the service life is likely to be reduced to some extent if a battery is subjected to rapid charging frequently.

Accelerated charging with a wallbox shouldn't be a problem for a vehicle battery - far removed from the stresses and strains of driving.

Note, however, that a charging power of z. B. 20 kW from a wallbox for a typical vehicle battery does not mean any particular load; after all, the battery must deliver much higher power (often more than 100 kW) at least for a short time when driving (especially when accelerating vigorously) and also start again when braking with energy recovery (recuperation). The service life therefore depends much more on whether the battery is often loaded by “sporty” driving with strong acceleration and strong braking.

In general, it can be assumed that batteries with a high capacity can withstand correspondingly higher charging power - and that they also need a suitable charging time.

Reporting and approval obligations; privacy

The distribution network operators are informed about all charging points in their area.

Since the operation of charging stations can in principle have a negative impact on the respective distribution network, there are reporting and approval obligations under certain conditions. In Germany, according to Section 19 of the Low Voltage Connection Ordinance (NAV), there has been an obligation to notify all charging points (including those with low capacities) since March 2019, i.e. an obligation to notify the respective distribution network operator. (This is the local network operator, not necessarily the electricity provider selected by the customer.) This gives the network operators an overview of the situation, which helps them to ensure network stability by taking appropriate measures, if necessary.

Above 12 kW (more precisely from an apparent power of 12 kVA) there is even a permit requirement, i. H. the network operator may, under certain circumstances, refuse to set it up or at least impose additional requirements that could increase costs.

All publicly accessible normal and fast charging points with an output of 3.7 kW or more must be reported to the Federal Network Agency at least four weeks before the planned start of construction. For fast charging points (from 22 kW) there is also an obligation to provide evidence of the fulfillment of technical requirements. The use of standardized plugs is also mandatory.

Various standards and regulations are currently being revised and could therefore be changed soon. Various legitimate interests must be agreed with one another here. On the one hand, the development of electromobility should not be unnecessarily hindered and made more expensive. On the other hand, it is of course necessary to avoid destabilizing the networks and incurring additional infrastructure costs.

In addition, data protection must also be taken into account in this context, in particular for billing the charging costs, for which some data must be collected. It will be necessary to set up appropriate procedures with the greatest possible data economy, for example to prevent the determination of movement profiles that could provide detailed information about the usage behavior of vehicle users.

Load management

The load on the battery is one thing, that of the power grid is another. This is not so much about the nationwide power generation, also less about the national power grids, but above all at two lower levels: to the local distribution grids as well as to the grid connections of individual residential complexes or commercial enterprises, e.g. B. for the supply of your entire fleet.

The distribution networks were set up decades ago with dimensions that did not allow for the operation of many electric cars. It was considered normal that individual households B. 5 kW for several plates of the electric stove, individual also z. B. 20 kW for an electric storage heater. But if every second apartment on a street comes with an electric car that needs to be charged with 20 kW or more, and this often at the same time (for example in the late afternoon after returning from work), you quickly reach the load limits of the local power grid. If these are exceeded, local power outages could also occur.

Unfortunately, it would be a very expensive company. B. to replace buried power lines next to the streets with stronger ones - in addition to the rest of the infrastructure, especially the distribution network transformers. Allocated to the individual households, this would be a considerable additional burden.

Because of the costs, it is also desirable for the individual customers of the energy supply companies to limit the required connection load. Some also have an electricity tariff with a power price that depends on the maximum power actually consumed. In some cases, charging stations are also operated as controllable consumer devices (with ripple control technology), which enables cheaper electricity tariffs.

So one tries to get by with the existing network capacities or with the lowest possible connection loads, wherever possible. With the increasing spread of electric cars, this will necessarily require a more or less sophisticated load management, and for some businesses this question is already very topical. Corresponding concepts are currently being discussed intensively and in some cases have already been implemented in practice. In the near future, this will have to be expanded, especially for the urban distribution networks, in order to avoid unnecessary cost burdens.

What use are fixed tariff times if all cars start charging at the beginning of a low tariff period?

In essence, the point is that the charging of many vehicles is appropriately distributed over time. This should of course be implemented without making the technology required for the vehicles or buildings significantly more expensive. The use of such facilities could be rewarded for vehicle operators with corresponding reductions in electricity costs. For example, you can work with a time-dependent electricity tariff - but ideally the tariff times are not fixed, but are based on the real situation on a daily basis. Corresponding information would of course have to be automatically transmitted to the charging infrastructure (e.g. via the Internet) so that they can optimize the charging strategy using their computers, e.g. in the charging devices, taking into account the wishes of the vehicle users. If, for example, a vehicle arrives at the charging station in the garage in the late afternoon and the station “knows” that it will be needed again the next morning at 8:00 am (with a certain minimum charge level), it can charge it to the cheapest Relocate night hours. Another approach would be to reduce the charging power in the case of several stations on a property as soon as several stations are used at the same time. However, this makes charging management more difficult to the extent that it is not known in advance when which power will be available and when.

In order to relieve the local distribution network as effectively as possible, the respective electricity price would have to be set separately for each residential area by the local network operator, who has the current data on the local network load and also knows the situation on the national electricity market.

Backup batteries are useful where charging cannot be postponed.

Another possibility is to use stationary backup batteries, which can temporarily provide additional energy in the event of bottlenecks. For such purposes, one may also use old vehicle batteries in the future, e.g. B. from vehicles that are otherwise no longer operational or if their capacity for vehicle use has decreased too much. Staggered charging is of course more cost-effective than using buffer batteries, but this is more an option for vehicles charged overnight than especially for motorway service stations, where fast charging is important.

With the mentioned technical measures of load management, expensive network expansions could be avoided. In addition, the use of renewable energies would be made much easier; For example, surplus wind power on windy days could be used specifically to charge many vehicle batteries, while vehicles would be charged more cautiously, especially during dark doldrums or when power plants fail.

One of the tasks of energy policy is to coordinate the development of meaningful solutions.

Obviously, it is highly desirable that there should not be a proliferation of the most varied of charge management systems, but rather a well thought-out, generally applicable approach. It is, of course, one of the tasks of energy policy to coordinate such developments in a targeted manner in cooperation with industry in order to enable solutions that are as economical as possible as soon as possible. A mess of uncoordinated developed technologies should be prevented from the outset and not replaced by a good solution later.

The concept of exchangeable batteries would of course make load management much easier, since these could easily be charged at the best possible opportunity. That would be particularly interesting for motorway service stations. However, it is questionable whether this particular use case would justify the widespread introduction of such a technology (with the involvement of many car manufacturers). For long-haul traffic, other mobility solutions (especially rail) should be used.

Feed back into the power grid

The contribution of electric cars to the energy transition could even be strengthened if it were to be fed back into the power grid (bidirectional charging). At critical times when there is a lack of electricity generation, energy could be taken from the vehicle batteries again, provided that the requirements of the vehicle users allow it. The additional technical effort compared to good load management (inverter, control, etc.) should be kept within limits. However, it is currently not yet completely clear how big the contribution to the solution would actually be and to what extent implementation is worthwhile. Finally, there are various other possible approaches.

Combination with the domestic solar system

For example, anyone who operates a photovoltaic system on their own home will want to use as much of the solar power as possible for their electric car. It is also of financial interest to charge the car primarily when solar power is available and is not already being used for other purposes (such as an electric boiler).This is because you receive a feed-in tariff for excess electricity that you feed into the grid, but this is now much lower than what you pay for electricity drawn at other times. So it's about maximizing self-consumption.

This goal can be achieved to some extent without additional technology, for example by plugging in the car for charging whenever the solar system is producing well. Of course, this approach has practical limits; For example, the year assumes that you are at home and can always pay attention to these things.

It works a little better if there is the option of scheduling charging in advance, either in the vehicle or in the charging station - for example when arriving home from a trip. Here, too, one would have to keep thinking about it, which is certainly not for everyone.

It is certainly best if charging is automatically optimized via a home energy management system. Such possibilities are likely to become more widely available in the near future, for example in connection with electricity tariffs that are flexible in time, as described above.

Charging infrastructure for tenants

It is often difficult for apartment tenants to obtain suitable charging infrastructure for an electric car. After all, such an infrastructure would have to be built by the homeowner and at least largely paid for, which as a rule cannot be forced to do so. Above all, if the tenant is primarily interested, an appropriate contribution to the costs should be considered, even if the charging equipment ultimately belongs to the owner and not to the tenant.

Of course, landlords should not simply ignore the tenants' requests, because charging points can be important features of the attractiveness of an apartment. For new buildings and major renovations, from 2025 there will also be an obligation to set up at least pre-cabling for charging points.

In principle, of course, the same technical restrictions apply as for homeowners themselves - for example, that it is often hardly practical to provide a charging station for vehicles parked outdoors (even on public property). In the case of apartment buildings, there are also requirements such as recording consumption and billing - either directly via the tenant's electricity bill or via a separate service provider. Access to the parking spaces equipped with charging devices must also be regulated. Overall, a number of aspects should be carefully considered in advance in order to set up a cost-efficient and sustainable infrastructure.

Usually only an emergency solution for tenants is to only charge the vehicle in other places - for example at public charging stations, e.g. B. in shopping centers or at motorway service stations. Sooner or later you will need charging at home. The obstacles on this path are one of the factors that are slowing down the spread of electromobility in the field of private vehicles.

Questions and comments from readers

Here you can suggest questions and comments for publication and answering. The author of the RP-Energie-Lexikon will decide on the acceptance according to certain criteria. In essence, the point is that the matter is of broad interest.

If you receive help here, you might want to return the favor with a donation with which you support the further development of the energy dictionary.

Data protection: Please do not enter any personal data here. We would not publish them anyway and we would delete them soon. See also our privacy policy.

If you would like personal feedback or advice from the author, please write to him by email.

By submitting you give your consent to publish your entries here in accordance with our rules.

See also: electric car, battery, capacity of a battery, load management, inductive energy transfer