CHARGING SPEED AS GAME CHANGER
TIME IS EVERYTHING DURING THE SUB-ZERO RACE. THAT'S WHY CHARGING SPEED IS SO IMPORTANT. ALTHOUGH CHARGING SPEED CAN BE AFFECTED BY MANY FACTORS. AN EV’S CHARGING CURVE IS ONE OF THE MOST PROMINENT. Study your ev curve - keep your eye on the record - and save precious time by efficient charging.
Many different factors come into play when you are charging, which is why it is important to understand EV charging curves, especially when using public or Level 3, DC fast charging stations.
Level 3, fast charging stations, deliver 200-920 volts of direct current (DC). Because the conversion of the electric current from AC (from the grid) to DC (for storage in the battery) takes place within the charging station, EV charging can be very quick, much faster than at home. Public charging stations now provide a range of charge from 50 kW to 350 kW; a hyper-Fast 350 kW letting you charge in as little as 30 minutes.
So what is a charging curve?
When charging an EV battery, the speed or rate at which the battery charges changes. This is illustrated by a charging curve, which shows the different charging speed from 0 to 100 percent of charge. The speed of charge is not constant. Essentially, the charging speed is faster when the battery is nearly empty and slower when it’s nearly full. Filling up a water bottle is frequently used as an analogy; when the tap is first turned on, the flow of water quickly fills up the bottle, so then the tap is turned down to control the flow, before eventually closing, to prevent the contents of the bottle overflowing.
Why does the charging curve matter?
Knowing the charging curve of your EV gives you first a better understanding of pricing for EV charging stations and secondly an insight for the most efficient charge. Although tariff structures differ between countries, networks and charge point operators, the rate or speed of charge is the main pricing feature. Public charging stations are more expensive than home charging, and the faster the charging rate, the higher the price per kWh.
And than there is factor time. Let's take for instance the Volkswagen iD4 which will quickly ramp up to its peak charge at 135 kW, then slow down to 100 kW from 30% to 50% of charge, and then drop down again to 80 kW through to 80% of charge. With a battery capacity of 82 kWh capacity, testing has shown that it takes about 38 minutes to charge the iD4 to 80 percent, but 65 minutes to reach 100%. This means the battery takes almost as much time to charge from 0 to 80 percent as from 80 to 100 percent. So with your eye on the record it might be smarter to make more but faster charging stops instead of waiting for a full charge.
At the other end of the spectrum, waiting until the battery is close to zero before charging up is not recommended either, since the time it takes for the battery reach peak charging places unnecessary strain on the battery. Indeed, this is why most EV manufacturers list charging times between 20% and 80%. Not only does it help increase charging speeds, but it also protects the battery.
Understanding the charging curve of your EV allows you to optimize charging times at public charging stations. So for long journeys like the Sub-Zero Race, it makes more sense to charge the vehicle to 75 or 80 percent and resume the journey, than to charge to full at each stop. There’s really no need to charge the EV to 100%.
It is important to remember that a battery is a system which stores chemical energy and converts it into electrical energy thanks to an electro-chemical reaction. This reaction is influenced by temperature and time, as well as the latest vehicle software updates. Each EV manufacturer uses different battery chemistries and cooling technologies, and each will have its own set of optimal operating and charging instructions.
At low temperatures, it takes longer for batteries to reach their peak charging rate; but high temperatures can damage the battery. This is another reason why charging rates automatically slow down when the battery is around 80 percent, to protect it from overheating. Manufacturers recommend maintaining the charge above 20 and below 80 percent to protect the battery and maximize the battery lifespan.
Other factors that can be taken less into account but still can affect the charging speed are:
Grid Capacity
Charging speed can be affacted by the capacity of the grid. Even most grids are well equiped to cope with the charging demand of EV's, during peak hours, the local grid capacity can hypothetically affect charging speed - dependent on demand.
Power-sharing Charging Hubs
Depending on the layout of each charging site, power-sharing can occur between charge points to optimize grid connections. So can the ouput of a busy 350kW charging station suddenly feed you with a 70kW charge. Their are two that can occur:
1) Dual charging on a single charge point: When two cars are plugged into the same charge point, the total kW is divided (for example, a 50 kW charge point will deliver 25 kW to each connected vehicle). If only one EV is connected to a dual charge point, it will receive the maximum kW available.
2) Similarly, busy charging hubs may limit the maximum kW when energy demand is high. This occurs when multiple electric vehicles are charging at the same charging hub location. For instance, if 5 charging stations offer 350 kW, and 5 EVs are plugged in, it's likely that you'll average around 70 kW throughout your charging session.
Maximum Charging Rate of Your EV
Each EV comes with its own maximum charging rate, and these rates vary! The maximum charge rate represents the EV's battery charging capacity; connecting to a charging station that exceeds this limit will result in the EV drawing only as much power as is safe.
For instance, the Volkswagen ID.4 has a maximum charge rate of 118 kW. This means that even when connected to a 350 kW charger, it will never draw more than 118 kW. Additionally, the ID.4 is equipped with an onboard charger with a maximum rate of 7.2 kW. Therefore, when plugged into a 22 kW AC charger, the EV will never draw more than 7.2 kW.
Thus, it's essential to verify if your EV can make use of the maximum power at a charging station before plugging it in. So other Sub-Zero teams do not have to wait for their optimum charging station.
State of Charge (SoC)
The battery level indicates the percentage of charge remaining in your EV's battery (for example, 34% remaining).
EV batteries can accept more power from a charging point when their battery level is between 20-80%. If you begin charging when your battery level is at 8% or 89%, the charging rate will slow significantly. This is because the EV is safeguarding the battery from receiving excessive amounts of energy.
Charging Type (AC/DC)
Are you connected to an AC or DC charger? AC chargers generally charge at a slower rate because the energy conversion takes place through the EV's onboard charger rather than through the charging station cable/connector (as with DC charging stations).
Ambient and Battery Temperatures
The ideal temperature range for lithium-ion battery cells is between 15 and 45 degrees Celsius. If the temperature of the battery cells falls outside of this range, it can lead to damage. To maintain the battery at the optimal temperature, the EV either employs cooling systems or gradually warms the battery to prevent short-circuiting. In both scenarios, the EV will decrease charging speeds to safeguard the battery from potential damage.
Cable Capacity
In the realm of EV cables, size plays a crucial role. To accommodate high levels of electricity, cables need to strike a delicate balance: they must possess a sufficiently large diameter to handle power delivery without becoming excessively heavy due to added insulation.
In essence, cables constructed from thicker wires provide less resistance to the flow of energy, resulting in faster charging speeds!