What most of us call "batteries", for example "pencil batteries", are actually cells. We only refer to a battery as a set of electrically connected cells. The basic parameters of a battery are minimum and maximum voltage, capacity and internal resistance.
What most of us call "batteries", for example "pencil batteries", are actually cells. We only refer to a battery as a set of electrically connected cells. The basic parameters of a battery are minimum and maximum voltage, capacity and internal resistance.
The minimum and maximum battery voltages are the limits beyond which battery damage occurs. Capacity indicates how much energy can be stored in the battery. Internal resistance affects how much power can be extracted from the battery. We'll discuss the last two values in a little more detail, because in an electric car they fundamentally affect its performance.
Battery power (kW) depends on internal resistance
The internalresistance of the battery affects the maximum power that can be discharged or charged and affects the heat loss inside the battery. It is therefore crucial for the dynamics of the electric vehicle and the length of the charge.
The lower the internal resistance, the higher the performance. This is usually given in watts (W) or kilowatts (kW) and expresses the intensity of the work. If we are working very intensively, we are delivering high power. If we work extra long hours, we do a lot of work. In electrical engineering, we most often calculate power as voltage (in volts V) times current (in amperes A).Tesla car batteries with very little internal resistance can deliver over 500 kW. This represents power for 500 kettles or a large office building.
Battery capacity (kWh) is the energy supply
Battery capacity is crucial to the range of an electric car. The lower the capacity, the shorter the range of the electric car. When we talk about battery capacity, we usually refer to watt hours (Wh) or kilowatt hours (kWh). That is, what maximum power the battery is capable of delivering for one hour. Sometimes we may come across a capacity in Ah (this is how the BMW car company states it). If we then want to find out how much energy (Wh) is stored in the battery, we have to multiply this figure by the battery voltage (V). Thus, using the formula Wh = Ah x V.
We refer again to Tesla electric cars - these batteries have a capacity of up to 100 kWh. This amount of electricity would cover the consumption of a family home for 14 days.
We then calculate the range of the electric car by dividing its capacity by its consumption. This can be around 13 kWh/100 km for smaller cars. For large, powerful SUVs, it can be as high as 25 kWh/100 km.
Battery heating, cooling and temperature effects
The internalresistance of the battery indicates the maximum power that can be discharged or charged and affects the losses that occur inside the battery. A battery with a high internal resistance will experience high current draw losses and will therefore heat up more. For this reason, manufacturers sometimes use active battery cooling.
We know from experience that the range of an electric car will be different in winter and summer. The winter range is of course significantly shorter. Less knowledgeable owners and drivers or reviewers attribute this difference solely to the heating consumption of electric vehicles. However, the range in colder periods is particularly affected by the temperature of the battery, on which the internal resistance is dependent.
As the temperature drops, most chemical reactions slow down - in the human body as in a car. The one that takes place inside lithium cells is no exception. From the outside, this property appears as an increase in internal resistance. And here we return to the beginning of this paragraph: high internal resistance = high losses inside the battery. This is why some EV manufacturers use active battery heating.
If the battery is not actively conditioned, the power is temporarily reduced to prevent damage to the battery due to exceeding the threshold temperatures. With conditioned batteries, the performance is stable.
Extreme temperatures, storage
At very low temperatures (around - 20 °C), the internal resistance may increase to such an extent that the batteries cannot be operated. On the other hand, temperatures slightly above zero slow down the static ageing of the battery. During operation, high temperature has a positive effect on the internal resistance (i.e., increased power, reduced losses and faster charging). However, the maximum temperature must not be exceeded, which would lead to irreversible damage to the battery. A moderate temperature is best for battery storage, which will slow down ageing, especially when the car is not in use.
Illustration source: Hybrid.cz (homepage) / Devinn archive
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