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Fixing a broken J1772

Sat May 19, 2018 6:54 am


About three months ago I fell against the J1771. The next morning I found the car had not charged; the plug was at an angle because the latch tooth had broken off. It would still charge our cars but the proximity sense did not work unless I manually remembered to push the latch.

A couple of weeks ago, I bought a replacement J1771 connector from Amazon and installed it on the BMW L1 charger.

Survey Replacement

The first step is to disassemble the replacement. It came in without any instructions so this assumed some degree of understanding.

The shell is held together by Torx screws that were easy enough to remove:

Inside we find a the push button lever that activates a micro switch. This is part of the proximity sense circuit the car uses:

The plug is sealed using triangle screws. So I went to my favorite hardware store and bought a tri-wing bit which worked close enough for this first attempt:

So here is the shell, plug, and plug cover:

With the switch not activated, we measured 150 ohms:

Activating the switch, the resistance increases to 479 ohms that signals the car should stop charging. This avoids "hot" plug and unplugging that can lead to connector wear from small arcing:

Here are the parts of the plug:

There are five pins: ground is on the tab side; at the 2 o'clock position is the proximity pin; at 10 o'clock the pilot signal; 5 o'clock is the 'HOT' pin (black wire), and; 7 o'clock neutral:

This shows how the pins fit in the plug assembly:

Here you see all subassemblies together:

I bought a new stripper sized for power cables and a crimper tool. Sad to say, the crimper did not work out:

Broken Connector

Here we see the broken tooth off the retainer latch:

My Torx bit did not work because of the center pin. So I bought a set of security Torx bits:

The inside of the 2014 model year, J1772 was very busy:

Here is the latch with the micro switch and bundled wires, tie-wrapped together:

Here is the microswitch that converts the red and black wires to a ground and wire for the proximity circuit:

The next problem was the grommet that brought the cable into the handle. There were different sizes and incompatible:

The replacement grommet on the left is sized for a larger cable. The original cable only had to handle 15A so it was much smaller.

My fix was to wrap the cable with plastic tape to increase the diameter. This solved the grommet and internal cable strain relief clamp:

So I threaded the wire through the five connector holes and only needed to crimp the connectors:
Unfortunately the blue, pilot signal wire would not fit through the black plastic hole. So I used a drill to make it a little larger to fit.

There are three different connector styles. The HOT and NEUTRAL pins are identical. The ground pin is longer. Curiously the proximity and pilot pins are not identical:

The proximity pin on the left is slightly smaller than the pilot signal pin on the right:

Try as I might, I could not crimp the pins. So I soldered them:
Due to the size, a strong, solder gun is needed. But these solder cups do not have an air escape hole in the base. Solder can not flow through the whole length of the cup due to the trapped air.

The first plate on the left holds the pins into the connector assembly. A single Torx screw holds it, The comes the orange, water resistant rubber assembly. On the right is the last plate that forms a wall to the interior of the J1772 shell:

Another view showing the single Torx screw:

The water gasket is seated and the back plate ready to compress the gasket:

Here is the unit ready to seal up:

Finally, everything is ready for the smoke test:

  1. Assemble the J1772 using standard wire leading to four, automotive style, crimp connectors. This avoids having to fiddle with threading the power cable wires into the plug and a lot of experimentation.
  2. These are solder connectors so drill a small hole at the base of the cup so the solder can flow through and fill it completely. Since I did not do this, I'll use an IR thermometer to make sure there are no temperature hot pins.
  3. Wrapping the smaller cable with plastic tape is better than nothing, it is not an optimum solution. I will continue to look for better solutions like liquid tape and hoses whose internal and external diameters to fit.
Bob Wilson

ps. Before doing the smoke test, I noticed the AC plug was discolored so I opened it up:

So much for a water-tight, NEMA 5-15.
Last edited by bwilson4web on Mon May 21, 2018 4:40 pm, edited 2 times in total.
20k/27k mi 2014 BMW i3-REx
10k/10k mi 2017 Prius Prime

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Location: South Carolina

Re: Fixing a borken J1772

Sat May 19, 2018 9:55 am

Thanks Bob. Good write up

Posts: 1664
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: Fixing a borken J1772

Sat May 19, 2018 1:02 pm

The latch tooth/latch pin design seems to be a weakness in the J1772 standard. I have encountered several public charging stations with broken latch teeth which made using them very unreliable. Any disturbance of the charging cable or plug could stop the charging. And many i3 owners have had problems with latch pins that did not work correctly. Tesla and European Type 2 connectors (Mennekes) don't have latch teeth or latch pins and seem to function reliably. Maybe the new SAE J3068 connector design (similar or identical to the European Type 2 connector) will eventually replace J1772.

2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE

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Joined: Wed Jan 10, 2018 9:42 pm
Location: San Francisco Bay Area

Re: Fixing a borken J1772

Mon May 21, 2018 8:04 am

Nice work Bob. Thanks for sharing.

Soldering the wires should be much more reliable that crimps. Especially with the voltage and current going through those connections!

Posts: 4461
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: Fixing a borken J1772

Mon May 21, 2018 4:06 pm

FWIW, a PROPERLY crimped connection can be as good and may be better in some circumstances than a soldered one. But, having worked on military equipment, the proper crimping tool with the right-sized die that has been calibrated, is not something you're likely to see outside of a production facility, either commercial or military because of the high costs. A soldered wire connection is more likely to break from vibration than a crimped one, too, but not as likely to happen in this situation verses say on a missile.
Jim DeBruycker
2011 535i x-drive GT, 2014 i3 BEV

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