Category: Electric Vehicles

Back in January I posted the blog, which discussed the two competing standards for EV charging ports. This is the “Beta vs VHS” debate in the EV world that will determine compatibility between vehicles and charging stations. In just the short time since I originally wrote that blog, there has been a fair amount of activity.

There are two basic levels available today for charging EVs today. The first is the SAE J1772 standard which provides for “Level 1” or “Level 2” charging. This essentially refers to 120V AC household current (Level 1) and 240V AC (Level 2, household or otherwise), which provides at-home, overnight charging or “opportunity” charging at public stations. The second is DC fast charging, which allows vehicles to be fully recharged in less than an hour, and where this debate centers.

The two competing styles are the CHAdeMO and SAE J1772 “Combo:”

The competing standards are being pushed by both auto manufacturers as well as companies that are rolling out the public charging infrastructure (charging stations). Japanese automakers Nissan, Toyota, and Mitsubishi have been using the CHAdeMO standard for several years now, on a variety of cars. In North America, only the Nissan LEAF and Mitsubishi i-MiEV are equipped with this port currently. Even with only two vehicles sold with this port today, it still has the lions share of the current market- since the SAE “Combo” standard is still not being sold anywhere. With respect to available charging stations, more than 150 CHAdeMO stations are in use today, provided by Blink, Aerovironment, EATON, and other existing suppliers of stations and charging equipment. This is by far the dominant standard.

The SAE “Combo” standard is an up-and-comer, though. While not currently sold on any vehicles or available at any charging stations today, manufacturers such as GM, Ford, BMW, and Volkswagen have announced that they will be supporting this standard in 2014 and later models. Additionally, Car Charging Group, one of the largest charging networks suppliers in North America, has announced that are endorsing the standard. While this is just one of many suppliers, it is one, and it is first. More are likely to follow.

To further muddy the issue, perhaps the most visible EV company, Tesla, has decided not to support either standard (not directly, at least). Their “Supercharger” stations, which provide for DC fast charging, use a proprietary setup. They have, however, announced that they will be providing an adapter to allow their vehicles to use the SAE “Combo” standard. Consider this at least a tip-of-the-hat towards the SAE standard.

This is far from over and I am sure will continue to evolve rapidly. If new vehicles like the 2014 Chevy Spark EV, which uses the SAE “Combo” standard, take off, it could be a game changer. Much like the Betamax vs VHS debate, it will only take one or a handful of early adopters to cause one standard to take off and the other to languish.

Those unfamiliar with the design or use of EVs may be interested to discover there is a heated debate going on about EV charging. As everyone is probably well aware, EVs’ Achilles heel is their range, which is a direct function of their battery capacity and thus their ability to charge quickly.

There are two basic schemes available today for charging EVs today. The most popular one (based on vehicles sold) is the SAE J1772 standard “charging station” that operates off of single-phase AC household current. The charging station manages the link from household

power to the vehicle much like an automated disconnect or GFCI does. The vehicle then has an intelligent, on-board AC/DC converter that rectifies the provided household current and steps up (or down) the AC voltage to a voltage that allows for charging the on-board DC battery pack. The original standard was written to provide for 80-A charging at 240V, although most implementations are 30A or less. “Level 1” indicates 120VAC charging (usually less than 16A), “Level 2” indicates 240VAC charging (less than 32A). Actual current usage is defined by the AC/DC in the vehicle. Most EVs and plug-in hybrid sold today are provided with some form of portable J1772 (Level 1) charging station that the operator can plug into the wall. Open-source DIY kits have even sprung up for these chargers due to their popularity and simplicity (essentially a contactor w/processor to communicate with the vehicle to negotiate the connection).

The second (and much less popular) scheme is DC fast charging. In this case the charging station not only provides a connection to the vehicle but also rectifies and steps up the AC to DC and provides a DC source that can be directly connected to the vehicle.

Direct DC charging has one primary advantage: the speed of charging. Every EV is designed to charge at slightly different rates, but when you consider the battery pack size (16kWh for the Volt, 24kWh for the LEAF, 85kWh for the upgraded Tesla Model S), it becomes readily apparent that with a maximum of 200A, 220V service at home, it takes a while to charge. If you need a charge in a hurry (especially crucial when on the road), high current and voltage is needed.

The primary detractor for DC fast charging is the requirement for a large and expensive power supply to provide the AC/DC conversion. This is not a DIY home project! Voltages greater than 400V and currents greater than 100A may be supplied to fast charge the vehicle (a depleted 24kWh LEAF battery can be recharged from nearly dead back to full in less than 30 minutes). These are not small systems and require a hefty electrical service from the local utility company to operate.

There is also a raging debate over the specification and connectors for DC fast charging, which has not been standardized yet. As of today, the two competing styles are the CHAdeMO and SAE J1772 “Combo.” CHAdeMO is a consortium of Japanese automakers that have specified a DC fast charge scheme and connector which has already been deployed on multiple vehicles (Nissan LEAF, Mitsubishi iMiEV, and others). The odd name is an abbreviation of “CHArge de MOve”, equivalent to “charge for moving,” also a pun for O cha demo ikaga desuka in Japanese, translating to “How about some tea?”.  This connector has the advantage of being the first put into production, as well as the flexibility of being deployed in conjunction with, or instead of, a Level 1 or 2 J1772 charge port.

The SAE J1772 “Combo” is, as the name implies, an extension of the original J1772 specification that combines DC fast charge contacts with the Level 1/Level 2 contacts in one connector and port. This simplifies the design, but the design is already at a disadvantage being second to show up to the party.

For certain this debate will rage on for at least a short while. Only time will tell which standard emerges as dominant.

I have already blogged about the popularity of EVs and Hybrids and the challenges of overcurrent protection. What about switching power? As I’ve mentioned loads upward of 400V and 400A are not uncommon in the electric motors that power EVs and Hybrids. Numerous other loads exist at these voltages where the traction battery (the high voltage battery used to drive the electric motor) is also used to power accessory loads such as air conditioning, heating, the 12V DC-DC that charges the 12VDC accessory battery, and other items.

As with many other components, EVs and Hybrids provide a unique set of requirements for switching loads:

• Automotive environment: Shock and vibration ratings, IP67 or better sealing , -40 to +85C (or wider) temps
• Wide variance between control & contact voltages: 12V (or lower) control, 400V or higher switched
• High isolation: As high as 1GΩ between coil and switched contacts
• Low contact resistance: High current loads, high efficiency needs, and packaging/temp constraints mandate low contact resistance

For very small current loads (under 1 amp) there are many options by the major manufacturers in DIP reeds. This will work for smaller reference circuits and very light loads. Similarly, FETs and other solid state devices can be used (albeit with constrictions on isolation and PC board trace routing). Solid state solutions are also usable at somewhat higher current loads, such as some accessory loads, such as an electric heater or air conditioner. These might  draw 20A, 40A, 60A, or more. Several mechanical relay options do exist from TE, Omron, Schnieder, and others. Formats may not lend themselves very well to automotive use where socketed solutions such as the Form A or Form C have dominated the industry. Solid state devices may prove the most flexible when handling these medium loads.

Unfortunately, there is one heavy load that should be addressed for safety concerns. Most EVs and Hybrids feature a main relay to disconnect the traction battery from the drive electronics when not in use. This functionality also extends to much smaller EVs such as golf cars and sub-25 mph NEVs (Neighborhood Electric Vehicles). Even still, these smaller vehicles may draw hundreds of amps continuously. This main relay may have to handle 400A, 600A, or more, depending on the vehicle. All such vehicles have devices to deactivate the main electronics from the pack with the key off, or to enable the connection to the charger, or both. I have even seen main relays like this used for smaller loads to provide a high-reliability, high-isolation break in the circuit.

There are several devices that can handle this function that are available, but none used as widely as the Kilovac family (https://relays.te.com/kilovac/). Kilovac is a brand that has been around since 1964. In 2002 Kilovac was purchased by TE Connectivity and experienced a whole new surge in popularity through their distribution network. Many devices use prior to Kilovac’s recent rise in popularity were “open frame” type devices that were primarily used in telco central offices to connect the DC battery supply used in central office equipment. I have seen more than one of these (many more, in fact) that welded shut, sometimes with disastrous consequences. Terminal contamination, FOD, and any number of issues can cause these units to weld up. While they were designed to activate heavy loads, they were NOT intended for automotive duty or exposure to the elements, which is inevitably how they were implemented in vehicles (not in-cabin, but in an engine bay or trunk area).

The Kilovac units provide a hermetically sealed unit that has excellent resistance to vibration, high isolation, and is even available with a “coil economizer” to help keep the continuous current draw down on the coil. It is compact and really an ideal solution for the EV world for these heavy loads.