Improving Electric Vehicle Charging Rates

Electric vehicle batteries have two main problems when it comes to range.

First, they can’t yet match the energy density of gasoline, which makes them bigger and bulkier than a gas tank.

Second, recharging is slower than filling a gas tank and a bigger battery simply increases the time needed to recharge. (Plus, it also adds weight to the vehicle, contributing to the first problem.)

Together, these limitations mean that an electric vehicle road trip consists of short stretches of driving punctuated by long periods for recharging.

The solution seems obvious: Find a faster way of getting electricity into bigger batteries. Indeed, it’s so obvious that Tesla has already done it with their “Supercharger.”

But what about electric vehicles that don’t have Tesla’s proprietary technology? Or, for that matter, electric vehicles based on gas-powered designs — such as the Mercedes B-Class— and plug-in hybrid electric vehicles such as the Toyota Prius Plug-in?

Figuring out how to get these types of vehicles to support larger batteries that charge faster will require product-specific design processes supported by iterative testing with functional prototypes. Nevertheless, there are a number of common factors involved when dealing with present-day electric vehicle charging technology that all engineers in the automotive industry should be familiar with.

Electric Vehicle Charging Technology

Electric vehicle charging technology can be divided into four “levels.” These are:

• Level 1 – charging from a 120V AC supply. This delivers a little over one kilowatt per hour, working out to 2–5 miles of electric range per hour of charge.
• Level 2 – charging from the 240V AC supply available in most homes. This delivers up to 7.2 kilowatts per hour and gives 10–20 miles of range per hour of charging.
• Level 3 – charging from a higher voltage DC supply. This requires electric vehicle supply equipment capable of delivering higher power. Two technologies exist today: the US/German SAE J1772 Combo and the Japanese CHAdeMO system. Both can provide as much as 90 kilowatts, depending on implementation, to deliver between 10–20 miles of range with just a 20-minute charge.
• Level 4 – the proprietary Tesla Supercharger, which provides up to 120 kilowatts to deliver 170 miles of range in 30 minutes.

Level 3 and 4 chargers, which deliver DC power to the battery, are known generically as “DC Fast Chargers.”

Electric Vehicle Plug and Socket Design

Most electric and plug-in hybrid vehicles use a five-pin design that complies with the SAE J1772 standard for Level 1 and Level 2 charging. A special cable plugs into a standard wall outlet and into the car. However, this socket cannot handle the higher current and voltages required for DC Fast Charging.

The CHAdeMO DC Fast Charging standard uses a bulky four-pin cable connector. Nissan and Mitsubishi both use CHAdeMO in their electric and plug-in hybrid vehicles. Its weakness is that it cannot provide Level 1 and 2 charging. Consequently, CHAdeMO vehicles must have two charging ports, one for Level 1 and 2 and the other for DC Fast Charging.

U.S. and German automakers prefer the SAE J1772 Combo DC Fast Charging plug design. This adds two pins to the Level 1 and 2 plug and socket, enabling it to handle the higher DC voltages. The advantage for automakers is that they only need one socket to provide Level 1, 2 and 3 charging. Additionally, the plug is somewhat smaller and easier to handle than the CHAdeMO offering.

Tesla uses a unique design for the plug and socket on their cars. They do, however, sell adapters so that Tesla drivers can take advantage of Level 3 charging stations.

Electric Vehicle Prototyping Challenges

The challenges facing carmakers wanting to launch an electric vehicle or plug-in hybrid electric vehicle include:

• Finding space for larger batteries
• Deciding how and where to integrate the charging point or points

For both, rapid functional prototyping offers a quick way to evaluate the fit of alternative designs and can shorten the time to market.

When it comes to batteries and battery packs, 3D CAD models don’t always highlight assembly challenges. That’s where functional prototyping comes in. With a physical, functional model of a battery pack and its surrounding components, it’s possible to quickly assess the feasibility of a design. Any changes identified can then be quickly incorporated, re-prototyped and retested.

Charging point integration also benefits from a formal functional prototyping process. This certainly goes for new, wholly electric vehicles such as the next-generation Nissan Leaf, which is rumored to feature inductive charging, where engineers are in the process of envisioning an entirely new type of vehicle and working to bring new technologies to market.

For vehicles also sold as conventional gasoline models or plug-in hybrids, charging point placement can also be a challenge. When it’s not feasible to repurpose the gas tank filler, sheet metal changes are needed to add comparatively bulky external socket(s) for electric charging. Working within parameters established by existing designs that may already be in production, these alterations are best tackled through functional prototyping.

The alternative is to be limited by the design for the conventional gasoline-powered vehicle, as was Mercedes when they elected to avoid sheet metal changes to their plug-in B-Class by using only the space allocated for the conventional gas tank filler. This meant there was no room for a DC Fast Charging socket, making the B-Class only chargeable via AC outlet — an odd choice when direct competitor BMW i3 can be charged at a public DC Fast Charging station in seven minutes, according to BMW.

For designers struggling with issues like these, 3D CAD simply isn’t sufficient to guarantee no-interference issues. On the other hand, functional prototyping is. By using functional prototyping technologies that can produce parts quickly, development time can be compressed and new products can be brought to market more quickly.

For a good example of how this process might work, check out our “Charging with Plastic” case study, which shows how we used CNC machining and plastic injection molding to prototype a complex charging inlet assembly for one of our clients.

Toward the Electric Vehicle Future

Manufacturers are eager to launch electric and plug-in hybrid electric vehicles, most of which incorporate DC Fast Charging capability. But with standards resembling the VHS-Betamax battle of the late 1970s, it’s difficult for them to know which approach to take. Rapid functional prototyping methods, such as those offered by 3-Dimensional Services, provide a fast and practical means of evaluating the innovative designs needed to move this growing sector of automotive manufacturing forward.

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