J1772 Charging Upgrade

What do you do with a working electric car?  Tear it apart and add more parts!

I bought the 120V charger with the goal of being able to charge up wherever I can find a 120V wall outlet.  That's great for home and any houses I visit or my work building, but electric vehicle charging stations with the J1772 plug are popping up everywhere.  I don't want to miss charging from one of these stations just because I don't have the right socket in the car.

I initially thought that I could install the J1772 socket and then run the power wires in parallel with the existing 120V socket and charging circuit.  Imagine my frustration when I found that you cannot derive the needed 120V neutral conductor from a 240V J1772 plug.  J1772 does specify a 120V option, called Level 1, but it's not supported by my Schneider unit and most other public charging stations.

So I had two tasks: step down from 240V to 120V and derive Hot, Neutral and Ground wires for the 120V circuit.  The solution comes in the form of a toroidal autotransformer.  I was given a pointer for this type of device to Toroid Corporation of Maryland.  They build a standard list of autotransformers, but I needed 240V in, 120V out and 15 amps of capacity.  As you can see from the table, they don't offer that as an off-the-shelf unit.  I contacted them and told them what I was looking for, and they replied back with a custom design, spec sheet and price quote.  I confirmed with my power engineer friend at work that this was, in fact, the part that I needed.  After confirmation, I sent my order in along with $228.41 and was told to expect it in a little over a week.

In the meantime, I worked on some prototypes to see where I would be able to fit it, in the tight confines of the front trunk.  I measured the available space with the battery box in place in the front trunk.  Then I built a cardboard mockup about the size of the real transformer.

I first tried a case with a clear removable cover from Polycase like I've used in other locations in the car.

It is definitely a tight fit!  Let's see how the plugs fit along the top edge... again very tight but not bad.

But my decision was made - the power sockets stick down too far to get the wires mounted and routed within the box.

I found this Cantex box at Lowes that just barely fits.  I held it in place with my endless supply of woodworking clamps, and drilled holes for the top and bottom bolts.  The top is a through-bolt but the bottom is a rivnut so the bolt head doesn't stick into the side of the battery on the other side of the battery box wall.

And here's the mockup with the transformer and both power sockets drilled and set into place.

Here's what the sockets look like from the top - just right.

Now we move on to positioning the real transformer.  You can also see the passive air vents I installed in the bottom and side of the box to help dissipate the ~94F heat the transformer will generate when I'm charging from a J1772.

You can see that it was custom built for me because it has my name on the label inside the wrapping!

Here's the test fit inside the box.

Here's the battery box back in place to show how it will look once installed.  What you can't see is I had to cut away some metal to allow the box to fit.  It was a curved piece of thin metal that was used to hold the spare tire in place.  No more spare tire, no more need for that bit of metal.

And here's how we access the charging sockets.  Both are waterproof in case some water gets in while I have the hood up during a charge.

I added some additional venting to the cover to make sure the heat isn't building up inside the box.

Here's the box, fully wired up inside.  Note the 3/8" hole drilled in the center of the transformer's potting material to allow me to run a big bolt through the box to hold it in place.  I also cut some steel spacers to size to center the transformer from side to side in the box to increase airflow.

You can't see it from here, but I installed the AVC1 board from Modular EV Power inside the box.  This board implements the car side of the J1772 safety charging protocol.  You could jury rig something up to fake it out, but for $37 on eBay you can't go wrong.  I hooked up 12VDC and ground, AC ground and a wire to the Proximity and Pilot pins of the J1772 socket.  I didn't take advantage of it yet, but it has normally-open and normally-closed relay outputs.  You could use this to light up an indicator that the car is charging or put an interlock so you can't drive the car while you're charging.  Not that anyone would every do that, of course!



If I had to do it again, I would use the newer AVC2 board, as it's enclosed in a nice box with better mounting tabs to protect the electronics.



I could have used twist-on wire nuts for the AC cabling, but I don't trust them enough to stay in place with all of the vibration this will be subject to.  I used Polaris connectors, which we use for high-current, thick-conductor bonding at my solar power company.  They're also dipped in plastic so they won't short out against anything else in the box.

Now that it was all wired up, it was time to test it.  I connected my Schneider station to a 240V breaker in my workshop.

This is the guts of the Schneider unit.  Technically it's not a "charger", it only delivers AC power to the charger mounted inside your car.  This is known in the industry as EVSE, Electric Vehicle Supply Equipment.  It consists of a couple of fuses, a contactor and a small circuit board that implements the EVSE side of the J1772 safety protocol.

I flipped on the breaker and the top green light lit up, signaling that it was receiving power and was anxiously awaiting an electric car to appear nearby.

The first test of my charging system was plugging in a 120V extension cord.  This tests whether the 120V hot, neutral and ground are wired correctly to the output cable, without involving the transformer.  Good news, it worked!  You can see the light in the extension cord and the voltmeter reading 119.8V at the output of the box.

The big test was now plugging the Schneider into my box.  For this to work, everything had to be wired right - the 240V from the socket to the transformer, the transformer to the 120V circuit, and the AVC1 board connected and properly talking to the Schneider safety circuit.  Happily, when I plugged in the J1772 and the thumb toggle clicked into place, the small LED lit up on the AVC1 board indicating it was ready for charging, then the contactor clunked in the Schneider, then the voltmeter showed 119.5V!  As soon as I pressed the thumb switch, the Schneider and AVC disconnected and power stopped flowing, just like it should, even with the plug firmly seated in the socket.

Declaring success, I will wait for Saturday to tidy the wiring inside the box, mount the box to the side of the battery box and install it back in the car.  Then I'll do the final wiring back up to the relay box and the rest of the conversion wiring harness.