By Craig Van Batenburg
In a previous column, I discussed the options for charging your electric vehicle at home or work. For those traveling, however, you will want to use a DC charger or “fast charger.” To achieve very short charging times, fast chargers supply very high voltages (300-500 volts DC) at very high currents (50 to 350 Amps).
SAE has set a standard for this type commonly called the “combo plug” or CCS (combined charging system) used by American and European OEMs as well as Honda. Most Asian brands, like Nissan, Kia, and Mitsubishi, use a different plug called CHAdeMO. Both the CCS and CHAdeMO do the same thing: charge a high-voltage battery very quickly. Chevrolet says the Bolt, supported by a CCS, can gain 90 miles worth of range in 30 minutes, 160 miles of range in 60 minutes, and a full 238 miles of range in about two hours. In colder weather it takes somewhat longer.
There was a time (before 2010) when electric vehicle owners seeking ultimate connectivity and charging at the highest possible rate would have to manually adjust their car’s charger to ensure that the charger did not pull more power than the circuit the car was charging from could supply. While Tesla’s 2009-11 Roadster may have a semi-intelligent system using GPS to remember which charging limits are required where, owners still have to enter applicable current limits when charging takes place in a new location for the first time if the charging location can supply less than the charger cable can pull.
But now the Electrical Vehicle Supply Equipment (EVSE) or “charger” eliminates all user interaction beyond plugging the J1772 connector in. The charger takes care of the rest.
In the previous article I discussed both Level I and Level II EVSE. In North America and some other parts of the world, a five-pin system is used for Level I and II. If you have a five-pin connector, look at the J1772 receptacle and you will see five pins. The three large ones are the ac lines and a ground (see pins 1, 2, and 3 in picture and diagram). The two smaller pins (4 and 5) are used for communication between the vehicle and the EVSE.
When the J1172 charger is taken off the post and brought to the car, there is about 12 volts on the pilot pin (pin 4 in picture and wiring diagram). The vehicle also has 12 volts at the pilot pin. Once plugged to the EV, a 2.74kΩ “sense” resistor pulls down the voltage on the pilot pin in the EVSE to +9 volts. The “pilot circuit” is sometimes referred to as the “communication” pin. When the EVSE senses that voltage drop, it generates a 1-kHz square wave that toggles between +9 and –12 volts. The diode in the circuit clamps this at –12 volts as a safety feature. The makes sure the EVSE knows it is connected to an EV and not something else.
Next, depending on the vehicle battery’s state of charge, it closes an internal switch that throws a 1.3kΩ resistor in parallel with the 2.74kΩ resistor. This reduces the total resistance to 882Ω and pulls down the positive peak of the square wave to +6 volts. The EVSE sees this as a request for AC power and relays in the EVSE box (attached to the cord at the building side) turn on to supply AC voltage to the charger in the car.
The other small pin is a “proximity” or “safety pin” (pin 5 in picture and wiring diagram). Once the electric vehicle is a plugged in and detected, the on-board system makes sure you don’t drive away while still plugged in. The vehicle may be programed to not shift out of “Park” (like a Chevy Volt) or never go into “READY” (like a Nissan Leaf).
The first fast charger sold, the CHAdeMO, is still used on the Nissan Leaf as well as other Asian brands. In warm weather, a first generation (2011–2012) Leaf can go from 20 percent state of charge to 80 percent in 30 minutes. It takes longer in cold weather.
Fail-safe during charging is done with two communication lines (CAN signal and Pilot signal) from the vehicle to the charger. They are in place to send a signal in case a malfunction is detected on the vehicle side. This way, charging will stop even if one communication line is broken. When the vehicle coupler is removed, the disconnection of the grounding wire and the pilot wire causes each pilot signal to turn OFF, which puts a halt to the DC output immediately, so that any electrical “arcing” will not happen. An “interlock” using a connector gives the controller in the “charging unit” (external from the electric vehicle) information to start charging and also the EV battery contactors to close and accept the charger. EV contactors never close and there is zero voltage at the charger port and connector (just like J1772) unless a vehicle coupler is connected to the vehicle.
A “pre-charge automatic safety check” is a test conducted before each charge to check the circuit insulation and the circuit between the charger and EV contactors. During charging, the vehicle coupler is locked to the vehicle inlet via a mechanical latch, and the mechanical latch is locked by an electrical lock. Once charging is completed (or the customer turns off the CHAdeMO manually), the electric lock is released after confirming the high voltage on the vehicle connector is off. If the voltage does not drop to a safety level, the lock will not be released.
CHAdeMO can deliver typically 50 to 125 amps, but is designed for up to 200 amps. The CHAdeMO voltage is 50 to 500 volts, but in reality the DC voltage just needs to be higher than the high-voltage battery in the vehicle.
The two big pins are positive and negative DC, pins 5 and 6. There is no high voltage ground, as the system is isolated. Then there are seven communication pins: two are a twisted pair for CAN digital communication, pins 8 and 9. Five are simple analog control pins, pins 1, 2, 4, 7 and 10.
The SAE CCS or combo plug was introduced in model year 2013 on some plug-in cars. It is competition to the CHAdeMO and is fitted to cars sold in North America that are American or European branded PHEV and EVs. In model year 2018, Honda started selling a plug-in with fast charging, but unlike the other Japanese brands, it used the combo plug.
The CCS uses the same two communication pins but does not use the three larger pins in the original J1772 connector. Instead, the CCS sends DC voltage directly to the high voltage battery pack through the lower two big pins. All three Levels (I-II and Fast Charging) now use the same port on the side of the car.
If you don’t have experience with electric vehicle charging, here are some tips. Stop at a charging station and talk to electric vehicle owners. Go to a dealership and test drive a plug-in vehicle. Go to the SAE website (www.sae.org) and read articles published (some are free). Visit your local electric utility’s website to see if they have charging station locations. Go to your state’s website and search for electric vehicle programs offered. And download an app that helps you find nearby charging stations where you live; a good North American website is www.plugshare.com.
Over the last year I have tried to explain what an American automotive technician needs to know to understand hybrids and plug-in cars. If you want to know more, go to our website (www.fixhybrid.com) and sign up for announcements, or follow us on Twitter or Facebook.
The future has arrived in the electric vehicle. Are you ready? •
Craig Van Batenburg is a former repair shop owner who is the CEO of Automotive Career Development Center (www.fixhybrid.com), which offers training and consulting related to electric and hybrid vehicles; he can be reached at Craig@fixhybrid.com.