Modular EV Power J1772 EVSE

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Adapters and J1772 connection problems on some new EVSE units

November 22, 2012

In October 2012 a new release of SAE J1772 was published. In a quick review there were no big changes for Level1 and Level 2 charging, see the bottom of this page for those notes.

Suddenly in mid-November something has changed and many new chargers don’t work with cars and adapters that worked before. When the first one appeared we thought it was probably a failure, then more problems started to appear. It took a carful full read to find them in the text of the new version of SAE J1772.

The first one is a recommendation to require every state for the pilot signal happen in sequence. The timing requirements in the standard do not require this but it is a recommendation of good practice from Appendix E, table E1 notes.. By requiring every state happen helps insure the plug is never mated or separated when power is on. The J1772 connector is not suitable for making or breaking a connection under load. Just using a resistor and diode can allow power to be active when the connector is separated or provide power before the connector is fully mated.

The 3 most common states in J1772 Level1 or 2 AC are A, B, and C

· State A is not connected.

· State B is connected but not requesting power. This is the diode and a 2.74K ohm resistor.

· State C is connected and requesting power. This is the diode and the 2.74K ohm resistor, the switch puts a 1.3K ohm resistor in parallel with the other resistor.

So under the new recommendations you start at A then MUST go to B and finally get power at C.

It makes sense and is logical. If you have a production EV with a computer power you are set.

If you are using a simple resistor and diode or one of the adaptors that have no switch the adaptor may no longer work because they skip state B.

If you have a unit with a switch, the switch MUST be OFF when you plug into J1772 then switch it on to get power. When it is time to disconnect, the switch goes off first then unplug. Don’t forget to make sure the switch is off next time you connect.

So what are you going to do now that what you have does not work?

If you have one of our Modular EV Power Adapter units we will add the switch and change the resistors if you send it back with $15 for return shipping. We will add a toggle switch next to the handle.

If you have a AVC1 or AVC2 module from Modular EV Power and got your inlet connector from us everything should work because it always starts at A then go to B when mated and goes to C when the latch is complete providing power. This what the AVC2 modules are intended to do. They also give you a relay contact to indicate when it is latched and requesting power so you can inhibit motion or do something else.

If you have a AVC1 or AVC2 module from Modular EV Power and got your inlet connector someplace else the resistor for state B may be wrong. To check it use an ohmmeter with the J1772 unplugged. Measure across the pilot signal and ground. The resistance should be 2,700 ohms or 2.7K ohms. If you have problems write us.

If you have been using a resistor and a diode here is the more advanced 2 resistor, diode and switch circuit.

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The second one is a recommendation to have a tighter voltage window for the states. The standard allows a +/- 1.0 volt window around the ideal voltages for each of the states. So state C is nominally 6.0 volts and the window is 5.0 to 7.0 volts. The recommendation of good practice now has state C is nominally 6.0 volts and the window is 5.48 to 6.49 volts.

This means using resistors that are close to the 2.74K ohm and 1.30K ohm may not work any longer. Everything from Modular EV Power uses 1% resistors of the exact value.

e-mail: david@modularevpower.com

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Original SAE J-1772 new update October 2012

October 12, 2012

The long awaited revision to SAE J-1772 that defines DC charging was released a few days ago.

Level 1 and Level 2 AC charging remain unchanged except for a recommendation that home charging be limited to 32 Amps.

But now there is Level 1 and Level 2 DC charging.

Level 1 DC charging uses the standard J-1772 connector used for AC charging. It can provide up to 80 Amps from a 300 to 600 volt DC source. A range of Pilot signal PWM has been defined to tell the EVSE to expect a digital data signal. I need to get the standards that explain the communication.

Level 2 DC charging uses the standard J-1772 connector used for AC charging along with the 2 new large extra pins. It can provide up to 200 Amps from a 300 to 600 volt DC source. A range of Pilot signal PWM has been defined to tell the EVSE to expect a digital data signal. There is a new layer of safety and interlocks for this high power connection and that all adds cost. A latch to prevent separation when power is on and temperature sensors in the connector are part of the safety.

My thoughts are the 32 at home limit will end up limiting the AC chargers in most commercial vehicles. It is simpler to charge from DC than from AC so commercial vehicles could have a 32 Amp AC system that also accepts 80 Amps DC for faster charging. I suspect the cost and complexity of Level 2 DC will keep it off most vehicles. It would be suitable for fleet vehicles trucks, busses that have a service center.

Here at modular EV Power LLC we are still refining our products for AC Level 1 and 2. We are working on EVSE Kits designed for 40 Amp beakers that give 31 amps to the car and ones designed for 100 Amp beakers that give 75 amps (limit of the cable sets) to the car. We are working on lowering the cost of the power meter and getting that data out to the user. Many people have asked for a delay timer or charge time control and it is being developed. Integrated GFI and a soft current limit are also coming. And to tie it all together a communications interface for remote monitoring of data.

e-mail: david@modularevpower.com

SAE J1772:2012(tm) is a trademarked standard of the Society of Automotive Engineers.