EV Fundamentals: J1772
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J1772
08.19
| 00:00 | In the previous section of the course, we took a good look at the onboard charger that nearly all electric vehicles use, and in this module, we're going to discuss exactly how these units interface with and receive a charge from the building's AC power supply using a special connector with a specific protocol. |
| 00:16 | Just like with the VHS vs. Betamax War of the 80s, or the more recent battle between Blu-ray and HD DVD, as any new technology emerges, a lot of different groups rush to hop on board and push their own standard. |
| 00:30 | EVs are no different, and as a result, we have a few different charging standards depending on where you live. |
| 00:36 | We'll look at what's known as Level 2 charging first, and then in the next module, we'll move on to discussing direct DC fast charging, which is called Level 3 charging, and doesn't use the vehicle's onboard charger. |
| 00:47 | If you're interested in EVs, no doubt you've seen some EV chargers attached to buildings, but like we touched on in the previous section of the course, in reality, these Level 2 chargers are not chargers at all. |
| 00:57 | They're just boxes that house two relays and some basic electronics to communicate with the vehicle. |
| 01:02 | These boxes are most often referred to as EVSEs, which stand for Electric Vehicle Supply Equipment. |
| 01:09 | With this in mind, we should always be wary of EVSEs that are massive and cost silly amounts of money. |
| 01:14 | They're very simple devices, and all of the actual charging happens in the vehicle. |
| 01:19 | When an EVSE is connected to the car, it tells the vehicle how much power it's able to supply, and then there's a short handshake process that occurs, at which point the EVSE will close its relays, connecting the vehicle's onboard charger to the building's AC power. |
| 01:34 | From there, the vehicle will respect the AC current limit that the EVSE reports, and the onboard charger will start converting AC power to DC, feeding that power into the battery. |
| 01:44 | There are two main Level 2 charge connector designs. |
| 01:47 | J1772 is a 5-pin standard that's used in North America, while the Type 2 connector, which has 7 pins, is the European standard of more or less the same thing. |
| 01:59 | That's pretty much accepted all over the world. |
| 02:02 | The main difference between J1772 and the Type 2 connector is that the additional pins of the Type 2 allow for multi-phase power supplies, which are more common outside of North America. |
| 02:13 | Many onboard chargers are able to accept 3-phase power, which greatly increases the power that they're able to provide the battery. |
| 02:19 | Tesla vehicles also use a different charger shape in North America, called the NACS, short for North American Charge Standard. |
| 02:26 | The NACS is slowly becoming the leading charge inlet design in North America, and not just for Tesla vehicles. |
| 02:31 | It features a very compact design, where the same two high current pins are used for both AC and DC charging. |
| 02:38 | Now, that you have an idea of the different standards and why they matter, let's talk about how the connection protocol works, starting with J1772. |
| 02:44 | There are 5 pins in the connector in total, 3 of which are larger, designed to carry high current. |
| 02:50 | These are Line 1, Line 2, and Ground, which is also known as Protective Earth. |
| 02:54 | The remaining 2 pins are the small control signals, called the Control Pilot and Proximity Pilot. |
| 03:00 | The large, high current pins are simple, they carry either 240V across Line 1 and Line 2, or 120V using Neutral on Line 2. |
| 03:08 | And the Ground pin connects the onboard charger to the same earth ground that the building is connected to. |
| 03:13 | The Proximity Pilot is a simple resistor ladder contained within the J1772 connector and receptacle. |
| 03:19 | 5V through a pull-up resistor is provided by the charger or controller, and through this resistor network, which is connected to ground, the controller determines the state of the connector based on the voltage. |
| 03:30 | The less resistance there is to ground, the further the voltage drops from 5V towards 0V. |
| 03:35 | The way the pull-up resistor works is that a small stream of electricity comes into the circuit, and if there is an equal amount of resistance to ground, the output voltage will be 15% of the input voltage. |
| 03:45 | So, in this case, that would be 2.5V. |
| 03:48 | If there was no resistance to ground, the output would be 0V. |
| 03:51 | To prevent the pins from being disconnected while high current is flowing, there is also a switch on the J1772 release button. |
| 03:57 | When pressed, this switch signifies to the charger that the user wishes to unplug it, and charging stops immediately to protect those pins from being disconnected while high current is flowing. |
| 04:07 | In total, there are three states that the Proximity Pilot pin will report. |
| 04:11 | Disconnected, as in the cable isn't plugged in, in which case the voltage on the Pilot pin will be 4.45V, as you can see here. |
| 04:19 | Connected, where the cable is plugged into the receptacle, in which case the voltage would be 2.75V. |
| 04:25 | And finally, with the button pressed, where the voltage will be 1.5V. |
| 04:29 | The Type II connector functions in a very similar way, although there is not a button on the connector, instead the connector is locked in by a solenoid. |
| 04:36 | The other small pin, which is the Control Pilot, also works similarly on both the J1772 and Type II connectors. |
| 04:43 | This pin serves to convey information bidirectionally between the EVSE and the onboard charger. |
| 04:49 | First, the EVSE sends a pulse width modulated signal through a pull-up resistor, with its duty cycle representing the maximum current it can supply, ranging from 6A at 10% duty to 80A at 96% duty. |
| 05:03 | It's important to note that the relationship between current and duty isn't linear. |
| 05:07 | Below 51A, the current limit is 60% of the duty, so 6A at 10% duty cycle is an easy example of this. |
| 05:15 | Presumably, because the peak charging current has increased to a higher value than the standard had first predicted, the formula actually changes above 51A. |
| 05:23 | This won't apply to everyone, but it's worth noting if you're programming your own controller. |
| 05:27 | So, we have this pulse width modulated signal coming from the EVSE. |
| 05:31 | The EVSE is able to tell when the onboard charger is connected because of resistor R3, which drops the voltage from 12V down to 9V when the EV is connected. |
| 05:41 | So, at this point, the EVSE relays are still open. |
| 05:44 | It's only when the onboard charger connects resistor R2 to ground, this pulls down the system's voltage to 6V, and now the EVSE sees that the car is making a command to charge, closing its relays, and giving the onboard charger access to the building's AC voltage. |
| 06:00 | It's all a bit of complicated analog signaling, but the cleverness is being able to accomplish multiple signals with few wires. |
| 06:06 | You could argue that two CAN wires would be a much simpler approach, but this analog signaling method is likely more robust and definitely cheaper to implement. |
| 06:15 | So, with two wires, the two devices are able to communicate and understand the following things. |
| 06:20 | If a connector is plugged into the vehicle or not, and if the button is pressed, regardless of whether it's connected to anything or not. |
| 06:27 | If the EVSE is connected to the onboard charger, how much current the EVSE can provide, if the vehicle is saying it's ok to start charging, as well as additional fault checks and reports. |
| 06:37 | If we're working on an EV conversion project, our J1772 circuit can either connect directly to an onboard charger that handles this communication for you, or to a third-party device that handles the signaling for you. |
| 06:49 | It's becoming increasingly common for chargers to directly handle this J1772 communication, which is really nice as it saves us from having to worry about all these details. |
| 06:58 | Of course, if you're doing your own EV conversion, you could also just put a regular dumb plug on a charger, it wouldn't be the wiser. |
| 07:05 | However, if the charger only knows it's plugged in based on saying AC voltage, the car won't know if it's connected to the building or not if the AC circuit is dead. |
| 07:13 | There won't be any way for the charger to know it's about to be unplugged, so arcing may occur in the connector, which will damage the pins. |
| 07:20 | Also, the charger won't know how much current it can safely draw from that circuit. |
| 07:24 | And most importantly, the VCU wouldn't have any way of knowing if there's a cable attached to the vehicle, so it could drive away with a cable plugged in. |
| 07:32 | So, take extreme caution if you're planning on taking the quick way around to setting up power to charge your conversion project. |
| 07:38 | It's always best to use an EVSE for these safety and reliability reasons. |
| 07:43 | Okay, let's cover off the main points that we looked at in this module. |
| 07:46 | What many commonly refer to as chargers are actually very simple devices that only supply power to the actual charger inside the vehicle. |
| 07:54 | These EVSEs use three different types of plug. |
| 07:57 | J1772, which is common in North America, NACS, which is slowly becoming the new North American standard and is based on the Tesla connector, and Type 2, which is used pretty much everywhere else in the world. |
| 08:08 | Although it's totally possible to just use a regular plug in a dumb charger on an EV project, it has its drawbacks, especially when it comes to safety, and it's not something we recommend. |
