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J1772:2010 Vehicle Inlet Coupler Design One Testing


The electrical  installation and wiring requirements in the USA are established by The National Electric Code, NFPA 70.  It has a section, 625, specifically about charging electric vehicles.  It sets up a set of requirements, mixes in SAE J1772 (TM) and third party testing such as UL.  It authority stops at the end of the charging connector.  The Vehicle Inlet Coupling is not detailed or covered in the NEC it is part of the vehicle.

Some basic testing is needed to consider making and sharing these couplings.  The design is sound so some electrical testing is needed.  The testing plan s simple, run 45 Amps through both power pins and measure temperatures. 

The 45 Amp AC current source will be a low voltage transformer powered by a variable transformer.  A resistor will be put in the primary lead to make adjustments less critical.  The current will be supplied to a UL listed 30Amp J1772 cable and connector set.  the connector will be mated with my J1772 design one connector.  The current will be set to 45 amps.  various temperatures will be monitored.  The center of my insulator near the ends of the pins, the center of the insulator at the bulkhead mounting plane, the actual power pin temperature, the shell temperature, and ambient. 

The connector and cord set are UL listed for 30Amp Charging.  This test is at 45 Amps is operating at 150% of that rating.  In this test there is no way to tell if the heat comes from my pins or the sleeve part of the connector.  The aluminum outer shell should conduct more heat away from the center and result in lower temperatures.  The resulting temperature will determine if this is a good solution.


This is a pin and sleeve connector so precision pins are needed. 

They are the electrical part in this connector.  The diameter of the power pin is just larger than US #8 wire.  So for a 30 degree centigrade rated system the pin is properly sized for 40 Amp service

The insulator goes in the body, the pins go in the insulator, and wires get attached to the pins. 

The power wires are #8 type THHN wire for a 90 degree centigrade rated system.  This is the maximum ambient temperature around the wire.

The National Electric Code, NFPA 70, only allows loads of 80% of a circuits maximum capacity (breaker size) as a safety factor and to prevent false trips of the protecting circuit breaker. 

Bottom line is the wire and pins are good for charging at up to 32 amps.

Holes were drilled and thermocouples were used to measure temperatures.

actual pin temperature
center of insulator at mounting flange
Center of insulator near inlet end
Connector Cable

In addition room temperature was monitored and an infrared thermometer was used to check the test setup and individual wires.

The complete set up.  It looks like a bunch of random junk but it is a good test.

The large variac reduces the line to voltage to a lower level.  A 750VA 12 volt transformer provides isolation and the high current needed.  The 12 volt winding is connected to the two power leads of the cable and connector.  The cable is uncoiled so it will not over heat.  The power leads on my connector (black) are connected together.  A clamp on amp meter is used the measure the actual test current.

During the testing components heated and the variac occasionally needed a slight adjustment to keep the current at set amps.


The first test was at 30 amps just to make sure it all worked and nothing got much to hot.  Temperatures in the connector stabilized in 5 hours with a rise of 20 degrees Fahrenheit in the center of the insulator.

The next test was 45 amps.  This will more than double the power lost to heat in these electrical parts.  Again in about 5 hours temperatures were stable.  The center of the insulator had a rise of  40 Fahrenheit this time but the pin because the hot spot with a 50 degree F rise.

One more test was at48 amps since 32 amps this is a popular charging current for older charging stations.  It is just 2 amps more.  This was a continuation of the last test but still took 5 hours for temperatures to become stable.  The center of the insulator rose anther 7 degrees for 47 Fahrenheit this time and the pin rose to 52 degree F rise.

Many NEMA electrical connectors are tested at 150% of rated load and are only allowed a 30 degree centigrade rise which is 54 degrees Fahrenheit.  This is very close to my results.  It must also be remembered that this coupler has an aluminum shell whose temperature rose be 25 degrees which should have helped keep the center cooler.

Just as an interesting note the transformer was putting out 5.78 volts for 48 amps and that works out to be 277 watts of power lost in the cable and connectors.  The out side of the cable was 22 degrees Fahrenheit warmer than the room and was obviously warm to the touch.



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