Home charging is the most widely used form of charging for EV owners right now, whereby an AC charging station is used to transfer AC power from the grid into an EV. Once transferred, the vehicle’s on-board charger converts the AC power into DC power to charge the battery. Due to EV space and weight constraints, on-board chargers and AC charging stations are typically limited to lower amounts of power (22 kW or less), resulting in slower charging times (several hours).
Certifications and accreditations have been introduced to ensure that EV charging stations are safely installed for home-use. For example, In January 2019, three important changes were made to the Wiring Regulations. Firstly, contractors must now use a socket specifically designed for EV charging. These sockets have uprated contacts and switches, can supply 10-13 amps constantly over many hours, and have “EV” marked on them. New rules with regards to earthing have also been given and lastly, contractors must ensure that a Type B Residual Current Device (RCD) is integrated into a charger/fuse board. Type B RCDs prevent leakage currents from reaching dangerous levels in charging stations. If an electrical fault occurs the station stops the power transfer immediately and de-energizes the cable, reducing electrocution and fire risk. As part of the Government’s Electric Vehicle Homecharge Scheme, The Office for Low Emission Vehicles (OLEV) provides a list of accredited installers for safer installations.
Correct usage also helps to mitigate risks. The Glovebox Guide, produced by Electrical Safety First, advises buying charging stations from a reputable supplier and ensuring certification for outdoor use. Avoiding “daisy chaining” cables together and checking regularly for wear and tear is also suggested.
It has been argued that driving an electric car is safer than a petrol or diesel vehicle. They also present a number of other benefits, such as zero-emissions at the tailpipe and noise reduction. As long as the proper protocol is followed, EV charging stations should not present any safety issues, however it is important to mitigate the risks – even more so when it comes to DC chargers.
DC charging stations convert AC power into DC power, which can be directly fed into a vehicle’s battery system for charging. As the conversion from AC power to DC power is done in the charging station, these units can provide higher levels of power (50 kW to 350 kW and beyond). This means faster charging times can be achieved (30 minutes or less).
DC charging stations are connected to the AC grid and installed on 3-phase utility supply (unlike single-phase supply connections for AC chargers). Therefore, their fuses (rated for AC protection) are larger than those used for AC stations and earth/ground-fault protection is necessary at both the AC grid side and the DC output side. Earth/ground-fault relays for DC voltage are utilised to detect electrical faults and minimize the risk of shock hazards to EV drivers.
As well as safety, efficient power conversion can be a major challenge when it comes to designing DC charging stations. The effectiveness of a DC charging station tends to be measured by comparing the amount of power a charger delivers to a vehicle against the amount of power it takes from the grid.
Single-phase cooling with MIVOLT can maximise charging station safety and power conversion efficiency. The range includes a K3 class fire safe variant (>300°C) that minimises fire risks and should a charging station cable break, not only will MIVOLT’s dielectric properties prevent conduction, but its non-toxic and biodegradable status will minimise both health and environmental impacts.
As non-conducting fluids, the range is simple to integrate into charging station cooling systems, flowing from the cable to a connector in a temperature controlled loop for efficient and effective thermal management.
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