Forget 400V – 800V is on the Way

Fast forward twenty years, and although the battery chemistry is now overwhelmingly based on lithium-ion (LI-ion), other changes in the battery pack have been modest. The operating voltage has crept up to around 400V; the capacity can be as low as 17kWh for mini cars, although high-end batteries for performance vehicles can exceed 100kWh.

Apart from any breakthroughs in battery design, EV capacities are expected to continue their incremental increase, although big changes are on the way in operating voltage. Say hello to a new generation of EVs, such as Porsche’s Taycan shown in Figure 1, that ditch the 400V battery in favor of an 800V system.

Why the push to a higher voltage? Two of the main challenges for EV adoption are limited range and long recharge times. Ultra-fast charging can help to mitigate both concerns, but a current-generation DC fast charger for a 400V EV can only supply 50–60kW power output, running at 480+ volts and 100+ amps. This can fully charge an EV with a 100-mile range battery in slightly more than 30 minutes.

For 400V battery EVs, the charging rate is limited by the practical cable size required to carry the charging current. Increasing the charging current translates into extra heat generation in the battery. An internal temperature that exceeds the safe operating zone in a Li-ion battery can decrease performance; if it gets too high, it can cause an exothermic reaction, thermal runaway, and a fire.

A higher voltage allows a lower current to be used when charging the battery, which reduces overheating and allows better power retention. This contributes towards a greater driving range. It also allows for weight reduction, as less copper is needed in the vehicle electric system. This allows for smaller motors, freeing up space in the vehicle for additional battery capacity to increase the range.

New generations of DC fast chargers running at 800V can produce 150–350 kW of power. But the design of an 800V EV requires careful new considerations for all electrical systems. DC voltages at this level are deadly on contact even if lower DC voltages are usually considered safe.

As a result, system reliability requirements are high across the board. A high-power three-phase EV charger needs mechanically robust plug connections as well as a reliable electronic safety system. The battery management system in the car maintains constant communication with the charging station. The power only flows with the charger plug securely seated in the charging socket and the battery charger transmitting a constant “ok” signal. The charging station instantly disconnects on any interruption to the signal.

How can RECOM help? We provide a range of low-power AC/DC modules, DC/DC converters, and switching regulators that match the battery charging application requirements for auxiliary supplies in a fast DC charger.

For example, RECOM’s RAC05-xxSK/480 was developed for the monitoring task in the charger shown in Figure 2. The AC/DC converter operates at input voltages of up to 528V AC, and so easily operates between two phases in the three-phase system. Isolated for voltages of up to 4kV, the 5W converter converts three-phase power into low DC voltages of 5 or 12V DC for the monitoring electronics. The AC/DC converter’s auxiliary power powers the handshaking system that allows power to flow only if everything else is in good order.

RECOM also offers a non-isolated 3.8VDC/3A supply for the wireless interfaces: the RPL-3.0, a tiny 3mm² buck converter with integrated inductor that features adjustable output and full protection (SCP, OLP, OVP, OTP, UVLO).

RECOM’s subsidiary company, Power Control Systems (PCS), can supply high-reliability custom battery chargers, conditioners and bidirectional inverters based on proven platform designs from three-phase AC supplies with power ratings of up to 30kW or even higher with paralleled units.