I often see the term level 3 charger used when someone is really talking about DC fast charging. I’m here to tell you that there is no such thing as a level 3 charger now there are four different charging levels available under the Society of Automotive Engineers surface vehicle standard J1772 but it wasn’t always that way.
What the J1772 charging?
The J1772 standard document started back in 1996 and it has been revised seven times the latest version is the 2017 version and only in the very first two versions of that document did it list a level three charging standard as a proposed method of charging, but it was never implemented and has never been used as a matter of fact, in the 1996 version, it was referring to DC charging in the 2001 version it was referring to AC charging.
The J1772 standard is only for conductive charge couplings where you take a charge cord and physically plug it into your charging port on the vehicle there is also a J1773 standard that is an older one for the inductive charge couplings in this blog. I will show you the for real charging system power levels and types as outlined in the latest version of the J1772 standard from the Society of Automotive Engineers okay to understand the four different charging methods and levels you really need to understand some basic terminology and electrical principles the first thing to understand is that all electric vehicles and plug-in hybrid.
Electric vehicles use two different direct current DC batteries the first is a low-voltage 12-volt battery just like any other car has the second is a high-voltage 300 to 800 volt battery the high voltage battery supplies power to the inverter which drives the electric motors it also supplies power to the air conditioning compressor and to what is known as a DC to DC converter which is used to charge the low-voltage 12-volt battery the 12-volt battery supplies power to everything else on the vehicle like lights window radio’s locks etc now.
DC batteries like both of these batteries we just talked about need to be charged with DC power as I just mentioned your 12-volt DC battery is charged with power from the high voltage DC battery your high voltage DC battery is charged by one of two methods when you plug your car into a charger, chances are that charger is fed AC power alternating current from the wall and most Chargers supply AC power to the vehicle now as I just said the batteries need to be charged with DC power but the Chargers are supplying AC power.
Why to charge your DC battery and converts that AC power into DC power?
So somewhere on the vehicle there is something called an on-board charging module and I have one right here this is from a 2016 Chevrolet Volt that and this is a small one the more power they can handle the larger they are on this side of the onboard charging module is that an electrical connector that receives AC power directly from your plug in charge port. So when you plug your vehicle in you’re supplying power to this connector and then this module bumps the voltage up to a high enough voltage to charge your DC battery and converts that AC power into DC power and that DC power is available on this electrical connector so all plug-in hybrid and electric vehicles have an onboard charging module as I mentioned this one’s pretty small and this one is only rated at a maximum of 3.6 kilo Watts So as you can see in these photos here under the back seat of our Tesla Model S is a very large onboard charging module. You can see the onboard charging module under the rear hatch area of our 2018 Chevrolet Volt and under the hood here of our 2017 Chevrolet Volt Evi the onboard charging module each charging module is rated for a certain maximum amount of power that it can handle. So the onboard charging module in our Chevrolet Volt right here is rated to handle 3.6 kilo watts or 3,600 watts and that comes from a maximum of a 240 volt source and a 15 amp current ratings, so if you multiply 240 volts times 15 amps you get 3,600 or 3.6 kilo which means thousand watts now.
The on-board charging module of our 2017 Chevrolet Bolt EV back there is rated for almost double, what the Volt could handle and that was at seven point six eight kilo watts or seven thousand six hundred and eighty watts and that comes from a maximum input voltage of 240 volts times a maximum current of 32 amps which equals 76080 watts.
Now the on-board charging module of our 2018 Tesla Model S is rated at nineteen point two kilowatts and that comes from a maximum voltage of 240 volts times 80 amps so 240 times 80 is 19200. As most of you know there are two different AC charging levels, level one and level two, AC charging level 1 is based upon a wall voltage of a 110 to 120 volts multiplied by whatever current. Your car can handle some cars have the current set as low as 8 amps by default and if you take 120 volts times 8 amps you’ll get a whopping nine hundred and sixty watts or 0.96 kilowatts as your charging rate and you’ll be there. When you trying to get your battery charged on that now, on most vehicles that charging level is adjustable by default, it’s set to the lowest level possible.
So that, when you plug in your charger at your house or apartment, or whatever that you don’t pop or blow the circuit breaker, needs to be rated for at least 125 percent of the charge rate of the vehicle level to is based on a higher voltage 208 to 240 volts. So a level 2 charger requires some specialty wiring in your house or apartment complex or wherever it may be now the second method of charging your high voltage DC battery is with DC current directly and by using DC current to charge your DC battery we bypass the onboard charging module and just feed directly to the battery and charge it without wasting any power converting AC to DC on your vehicle.
So DC Chargers also come in two different power levels: there’s DC level one charge with a maximum rating of 48 kilowatts and there’s DC level 2 charging with a maximum rating of 4 hundred kilowatts, the majority of DC charging stations are DC level 2 chargers. I’ve never seen a DC level 1 charger, however, Tesla vehicles with their unique charge port utilize much of the DC level 1 charging design and what I mean by that is if you notice on Tesla’s with their unique charge port that you can plug in an AC charger or a DC charger and it fits the same connector.
There are no pin differences everything just plugs in and it’s AC or DC so somewhere on the vehicle the Tesla has to decide is the Power Beam supplied AC or DC and if it’s AC then it has to use its onboard charging module to convert it to DC before charging the battery and if it’s DC then it can feed it directly to the battery but all with just one charge port which is pretty cool. Now another thing to understand is that the charging station that you plug into your car which is referred to as the off-board charger or the cord set the portable cord, that you plug into your car those do not determine the amount of current that your car needs. There’s a computer in your car that signals the off board charger or your court set and tells it how much current there how much power to supply to charge the battery on the car and that amount of current is variable based on the state of charge of the battery and several other factors.
So one more time it’s the computer on the car that signals the off-board charger or the charging station how much current to use so you could go to a charging station like these Electrify America charging stations here locally and as you can see there’s chargers that are rated as high as 350 kilowatts there’s some that are rated a 150 kilowatts and some rated at 50 kilowatts if your car can only handle 50 kilowatts or less you could plug in the 350 kilowatt charger, but it wouldn’t charge at 350 kilowatts. It would only charge at the small amount that your car would tell that off for charger to use, as an example the Chevrolet Bolt EV back there is rated for a maximum DC level to charge of 50 kilowatts but it can also handle an AC level one charge as low as 1.44 kilowatts to charge as high as 7.68 kilowatts, and a DC level to charge as high as 50 kilowatts. It’s the same vehicle you can plug different Chargers in and get different charge rates but once again the the car signals the charger as to how much power is you used while charging the vehicle now if we look at this charge receptacle from a 2019 Chevrolet bolt EV.
This is considered a level two charge coupler according to the Society of Automotive Engineers J1772 document a lot of people call this a CCS for combined charging system connector but nowhere in the J1772 document does it mention CCS or a combined charge coupler so that comes from someplace, else this charge receptacle is referred to as a CCS type 1 charge coupler and there’s a type 2 outside the United States and so on.
But when you go to a charging station you will see the letters CCS for combined charging system and what they’re referring to is that this electrical connector this charge receptacle is a combination of AC charging on the top the round part that you can see here with the five pins and DC charging on the bottom with the two large pins. So let’s explore this connector a little bit as you can see here there are seven contact terminals labeled one through seven contacts one through five are used for AC level one charging AC level 2 charging and DC level 1 charging. DC level 1 charging actually uses pins or contacts one and two to supply DC current rather than AC current contacts three through seven are for DC level 2 charging in other words, we don’t use contacts one and two during DC level 2 charging just contacts 3 through 7 now let’s look at the details for these contacts, notice contact 1 and contact 2 are both three point six millimeter diameter terminals rated for 80 amps at 600 volts maximum contact number one receives AC power from the L1 wire in your wall, during AC level 1 and level 2 charging it receives DC positive power during DC level one charging contact number two is connected to the neutral line in your wall, during charging for AC level one charging and it’s connected to the l2 line in your wall during the AC level 2 charging and it’s connected to DC negative during DC level 1 charging so once again these two terminals contacts number 1 and 2 can be used for AC or DC charging with 80 amps maximum at 600 volts contact number 3 is used for all levels of AC and DC charging contact number 4 and contact number 5 are both 1.5 millimeter 2 amp 30 volt maximum terminals contact number 4 is called control pilot or CPE. It uses a 1 kilohertz or 1000 Hertz pulse width modulated signal the pulse width is a variable signal and is controlled by the vehicle and it’s read by the off-board charging module, so they can increase or decrease the pulse width to increase or decrease the amount of current being supplied to the vehicle that same line can also be used to indicate that communication is necessary and there’s actually power line communication available over the conductors on some vehicles contact number 5 is used for two things the first thing is for what is called control status and what that means is when you plug in your external charger to the vehicle all of those external chargers have a release button right there that unlocks the connector from the vehicle well when you push in on that release button there’s actually an electrical switch in there that opens and it signals the charger the external charger to shut off so we know that if you’re pushing that button in that you’re either making a connection or disconnecting and while you’re making a connection it’s not powered up anyway but if this is plugged into your vehicle and charging and you just walk up to it and hit this button and unplug it as soon as you hit that button within so many milliseconds the charging system is supposed to shut down. So that you’re unplugging a dead circuit and there’s no live power there so that is the control status there now the second thing contact number five is used for is called proximity pilot and what that means is when you plug the external charge cord into your vehicle it has to detect that it’s plugged into your vehicle and it does that quite easily because in the charge connector itself in between terminals 3 & 5 is a 2700 ohm resistor and when you plug this in the charger has its own parallel resistances and it’ll create a certain voltage drop and so it knows when it’s plugged into your vehicle and when it’s not plugged in so once again contact number five does two things it detects when you press this switch and it detects when the charge cable is plugged into the vehicle and there’s a Federal Motor Vehicle Safety standard that says while this is plugged into the vehicle the vehicle shall not move more than 105 millimeters I believe alright now the last two contacts contact six and seven are much larger terminals they are eight millimeter diameter terminals they are rated at 400 amps maximum at 1000 volts so 400 amps times 1000 volts is 400,000 watts or 400 kilowatts and contact number six is used for the positive side of your DC charging contact number seven is used for the negative side of DC charging.
Then starting with the 1996 version of the SAE J1772 document as you can see, here it is called a surface vehicle recommended practice so it’s not a standard in 1996. It’s a recommended practice and that’s different than an established standard but starting with the 1996 version here, and carrying through I have four of the seven versions here. I’ve got the 2001 which is also a recommended practice and a 2010 which is also a recommended practice it wasn’t until a 2016 and 17 versions of the J1772 document, that they actually changed the name to a surface vehicle standard.
So it’s an established standard so five of the seven documents that I’ve referred you to in this blog were just preliminary. They were recommended practices and a lot of that if mission has changed over the years by the way the 1996 version of the J1772 document is 34 pages long and the 2017 version that you can see here which is considerably thicker has 116 pages. So there’s a lot of information that’s been added to these now in all of these SAE documents for J1772, they refer to something called EVSE and that stands for electric vehicle supply equipment.
So we’ve got this term EVSE that’s out there and is being used and has got standards set by the Jay 1772 document but I wasn’t sure where that came from so I did some research and found out that it came from the National Fire Protection Association and FPA. It’s their document number 70 called the National Electric Code or NEC and this is the latest NEC codebook right here of 2020 and it’s really thick and in this book there is an article number 625 right here and it’s titled electric vehicle power transfer system and I just want to read the very first paragraph because it defines what EVSE means, it says this article covers the electrical conductors and equipment connecting an electric vehicle to premises wiring for the purpose of charging power export or bi-directional current flow. So the NFPA and the NEC have standards for connecting the off-board charger to the power circuits and then the Society of Automotive Engineers has the J1772 document that has the standards for connecting the EVs II to your vehicle and then your vehicle takes it from there and this is for both AC and DC charging levels.
So the J1772 document has a whole bunch of standards as to how the external charger or the off-board charger or EVSE as its referred to interfaces with the vehicle and there’s a whole bunch of requirements to make sure that the vehicle is not damaged by the external charge and that everything will work, the way it’s supposed to work and just a word of caution about external chargers external chargers need to be certified by underwriters laboratory or Intertek here. In North America, to verify that they are actually following the SAE J1772 rules as far as interfacing with the vehicle, so that no damage will occur. So if you find a real sweet deal on a real inexpensive external charger, look to see, if it has the letters UL for underwriters laboratory or the word Intertek listed or certified by it, because they need to be certified in order to obviously protect your vehicle. If it’s not certified you’re taking quite a chance in just assuming that it’s going to plug in and work correctly without having any problems.
Post time: Mar-05-2024
