Safer Charging for Electric Vehicles

8th September 2022  |  Electric vehicle

Technological advancements in charging-station and vehicle-side power systems have seen the time electric vehicle (EV) owners wait to receive a full charge reduced from several hours in 2012 to around just 10-20 minutes today.

Drivers can also expect to travel much further than they did a decade ago when early adopters could typically squeeze a paltry 75 miles out of a full charge.

Comparing that figure to today’s 260-mile average range shows just how far EV and charging tech have advanced since those early days.

But while range anxiety and time-to-charge are no longer the concerns they once were for EV owners, today’s high-voltage power components present engineers and designers with a fresh challenge.

The drive systems on modern vehicles can operate at voltages of 400-800V, generating currents of 100 amps—and this means charging is potentially risky if designers fail to give sufficient thought to safety.

Vehicle-Side Risks—EV Batteries & Flammability

In the time it’s taken for the average EV range to increase by more than double, vehicle batteries have become smaller and denser.

However, the underlying technology has changed very little, and batteries are still comprised of a series of lithium-ion cells containing highly flammable liquid electrolytes.

During fast DC charging, when batteries are placed under exceptionally high loads, overcharging or overcurrents could cause the battery to overheat. A single cell igniting is all it takes to start a thermal runaway—a catastrophic chain reaction resulting in an intense fire with toxic fumes that is difficult to extinguish.

Vehicle-Side Solutions

Moving from 400V to 800V drive systems could help solve the problem, and several significant manufacturers have already made the switch.

Audi, Porsche, Hyundai and Kia are among those already taking advantage of the space and weight gains from higher voltage drive systems, which require fewer large cross-section cables to carry power.

The newer 800V systems also allow for much faster charging—around just seven minutes when hooked to the latest generation of 350kW ultra-rapid chargers—so it’s hardly surprising that some experts believe 800V architecture across the whole EV market could soon become the standard.

Charger-Side Risks – Short Circuits and Ground Faults

It isn’t just vehicles that are prone to potential risk. Chargepoints spend their working lives exposed to the weather and are prone to short circuits and ground faults, usually as a result of the gradual wear and tear of insulation.

Several points in the circuitry require robust short-circuit and ground fault detection and protection.

The AC input stage, where power is rectified before being limited by a power factor corrector, is particularly vulnerable to excess load and benefits from ground fault detection and fast-acting fuses.

Meanwhile, the DC-DC conversion and output stage, where voltage is adjusted to the required level before outputting to the vehicle, is vulnerable to surges. So, in addition to ground fault protection, the DC stage requires constant monitoring and reliable filtering.

It also requires primary surge protection from varistors and diodes backed up by secondary protection devices to trip the circuit in case of a surge.

Staying Safe

Although many early concerns about EVs like range and time-to-charge are no longer as pressing as they once were, the race for ever more compact & high-performing components continues.

And with every gain, engineers and designers must work to keep up with the advances by making safer, more reliable vehicle and charger-side components and following common-sense precautions when designing, installing and maintaining systems.

Design and Dimension

Given the trend toward ever smaller and more compact power systems, designers must maintain the balance between appropriate thermal and electrical dimensioning and the need to keep down bulk and weight.

Choose Rugged Components

Both chargepoints and vehicles spend most of their working lives exposed to the elements, and vehicle components face the additional challenge of being constantly exposed to vibration. Such wear and tear is unavoidable, but you can give your systems the best chances of success by choosing robust components designed to last.

Future-Proof Your Safety Systems

Regular chargepoint and vehicle safety inspections should be a feature of every conscientious EV fleet owner and infrastructure provider’s standard operating procedures. You should ensure these go efficiently with a spacious design for ease of access and clear labelling of fuses and other protection.

Know the Legislation

Get familiar with the safety standards and best practice on EV charging. The RISCAuthority has published an extensive set of recommendations on fire safety for EV charging. The Institute of Engineering and Technology has also published a code of practice covering chargepoint installation safety.

Get Independent Advice on Safer Charging

For independent, unbiased advice about safer charging systems and components for high voltage vehicles, get in touch with Dalroad’s in-house engineers to discuss your project.

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