Calculating the consumption of an electric car seems simple, the data is shown to us by the car’s computer. However, it is not so simple as was discovered by the German Automobile Club ADAC.
You can lose a lot of electricity when charging an electric car. This applies not only to fast AC chargers, but also to « slow » charging in home connections. At the ADAC, they assert that we cannot avoid imposing losses entirely, but we can reduce them significantly.
The cost is not insignificant
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There are more basic options for charging an electric car at home, and the speed at which we will be charging it is also different. You can, for example, charge an electric car with a power of up to 2.3 kW on a Shuko socket, of course, depending on the capacity of the home network, and on a « wall box » charger it can be charged at a power of up to 11 kW, again of course depending on the capacity of the home network. If the power grid operator enables this, then charging at home can take place at a power of up to 22 kilowatts, which is more an exception than the rule.
At ADAC, four electric vehicles, the Renault Zoe, V ID.3, Tesla Model 3 and Fiat 500e, took charge loss measurements on a 2.3 kW power socket, an 11 kW wall charger, and a reduced power wall charger. The results of the measurements clearly showed that the losses during shipment largely depend on the method of shipment.
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Undoubtedly, charging with an 11kW wall charger has proven to be more efficient than charging via a shuko socket. The differences were largest while charging the Renault ZOE, and smaller while charging the Volkswagen ID 3. On the other hand, the Fiat 500e is clearly optimized for high charging efficiency, with losses being minimal in both cases.
ADAC has also measured losses that may occur when charging with a low-power wall charger. In practice, this can happen when the charging station distributes its power between two or three cars, or if the car is charged with electricity from solar cells. Also in this case, the measurements undoubtedly showed that higher charging power causes lower losses during charging.
sources of losses
Since high voltage batteries can only store direct current, and home chargers use alternating current from the grid for charging, this must be converted into direct current with the help of an onboard charger. This may lead to losses.
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In addition, electrical losses also occur in the 12-volt auxiliary electrical system, since many components that manage the charge are energized while charging high-voltage batteries. Only for its operation, 100 to 300 watts of electricity is required. Less than a percentage can also contribute to losses from thermal management of batteries, which are generally not considered critical when charging at home.
A long charging cable can also contribute significantly to losses during charging, and your home network can also contribute up to four percent, which can be a particular problem in older homes. If the owner is in doubt, he can ask electricians to check the condition of the home’s network, even if it is able to support continuous charging for electric vehicles.
Losses are greatest when charging with the help of a Shuko socket, in this case they reach 10 to 30 percent, but they are much less when charging via a wall charger, because they reach “only” 5 to 10 percent. There are several reasons for this.
Faster Shipping and Less Loss
Charging via the wall connection is usually three-phase (rather than single-phase via a Shuko socket), and thus allows for higher charging power. In addition, the electrician connects the wall charger to the network via stronger cables, so there are almost no losses in it. The conversion of AC to DC in the car charger is still continuous, so there are still losses in it. On the other hand, much less current is used for the electronics that manage the charge. That is, the battery is charged faster with a stronger current, so secondary consumers of electricity are also turned on for less time.
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When charging with alternating current, it is considered that the higher the charging power, the shorter it is, and therefore the lower the charging losses. If the owner of the electric car wants to avoid high costs due to losses, then it is recommended to charge it at a residential charging station at the maximum power allowed by the network. Measurements also showed that it does not matter at what level or at what level the battery is charged, since this is almost always equally effective, unlike fast charging with direct current.
The reason for Zoe’s differences
So buying a wall charger is worth it anyway, and this is even more evident on some cars. For example, in the case of Renault ZOE, the difference in losses between charging with a Shuko socket or an 11 kW wall charger is 14.5 percent.
Dusan Lukic, head of the new mobility project at Porsche Slovenia, notes that Renault ZOE is treated less unfairly by comparison. All other cars tested in the test are more modern and have dedicated built-in chargers that convert alternating current to direct current. The Zoe, on the other hand, is an old build, and the electric motor’s control electronics are concerned with current shunting. On the other hand, this arrangement enabled it to use alternating current up to 22 kW and more very early on, but it is worse when charging via a shuko socket or when charging with alternating current at lower power.
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For the same reasons, ADAC states, when charging electric vehicles, they recommend the use of a high-power AC wall charger or general charging connections. He adds that for the average owner of a Renault Zoe, for example, it is enough to charge once or twice a week at the same time that he makes larger purchases at a public charging station in a shopping center, and if he can of course have one at home, he should The socket is used only when there are no other options. In such a situation, possible losses during shipment will not be so significant.
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In Porsche Slovenia, when charging at an 11 kW wall hook or public charging station, they count on losses of eight to ten percent and also take them into account when notifying their customers when making a purchase. If the consumption of a particular car from the factory is 18 kWh / 100 km, it is increased to 20 kWh / 100 km to take into account the charging losses. He adds that a 9% loss due to the auxiliary systems running when charging on a powerful AC charger is perfectly acceptable, but anything less than that is actually very good.
We take research with a grain of salt
Andrej Pečjak, director of the Metron Institute and pioneer of electric mobility in Slovenia, views the results of ADAC’s research with some caution. He says losses when charging an electric car depend primarily on the charger built into it, not so much on the port or charging station. Namely, chargers have different efficiencies ranging from 88 to 96 percent, which manufacturers generally don’t mention. He adds that the charging station is only a hinge through which alternating current flows, and cannot affect losses.
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Pečjak also says that charging via a shuko socket is not recommended because these are not designed for a DC current of over 10 amps, which is required to charge an electric vehicle. If this socket is overloaded, it will overheat and fail. Due to overheating, additional losses of electric current may occur, but in this case there is a greater risk of melting the socket. According to Pečjak, when buying a wall-mounted charging station, it is important to pay attention to the fact that it can be repaired later, that the electronics are not completely immersed in the structure, and that it allows dynamic charging, which means that it automatically adapts to the current load on the home network.
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