Introduction: Building an OpenEVSE

An EVSE (Electric Vehicle Supply Equipment), more commonly known as a charging station, is the equipment to which an electric vehicle connects to charge its batteries.  Most (all?) electric cars sold in the United States recently conform to the connection standard J1772.  This Instructable describes the building of a level-2 (fast) J1772 charger.

If you've been researching building an EVSE you've probably heard this before but I'm going to say it again:  This project is not for beginners.  The voltages here are lethal.  If you are not experienced and comfortable working with 240V power lines then please STOP HERE.  If you proceed without a good understanding of how to work with these voltages and currents you are putting yourself and others are risk.  There is also the very real possibility that a mistake in the wiring could do serious damage to your vehicle.

All that being said, if you do a good job on this you will have an EVSE that is well built and properly implements all aspects of the J1772 standard, something that cannot be said about all commercial EVSEs.

I'm not going to give detailed step by step directions here.  If you need step by step directions then you probably shouldn't be doing this project by yourself.  It's just too dangerous.  Instead I'm going to show you what parts I used, how I put them together, and give some construction hints.

Step 1: Links to Other Pages

Step 2: Supplies

I believe this is a complete list of parts:
  • Open-EVSE 30A kit ($212.50) Open-EVSE
  • J1172 plug and cord ($173.36) Leviton A3435-PEV
    • I really like this particular cable.  It's heavy duty and seems like it will stand up well to being dragged across the floor.
  • Dryer cord ($22.96) Home Depot GE 4-Prong 30-Amp Dryer Cord
  • Acrylic sheet 0.20" thick (~$20) Home Depot
  • Enclosure ($43.00) Digikey 377-1788-ND
  • Pushbutton ($5.12) Digikey CWI265-ND
  • Cable glands & nuts ($8.64) Digikey:
  • Quick connect 0.25” 10-12 AWG ($2.39/15) Home Depot Gardner Bender 12 - 10 AWG 0.250 F-Disconnects
  • Quick connect 0.25” 18-22 AWG (2x $0.13) Digikey A27817CT-ND
  • Quick connect 0.187” 18-22 AWG (4x $0.14) Digikey A27804CT-ND
  • Hookup wire, AWG 12, THHN insulation
    • For connecting between fuses and relays.  In a cable AWG 10 is required for 30 Amps but for hookup AWG 12 is fine.
  • Hookup wire, AWG 20, 300V insulation
    • Make sure the insulation is at least 300V.  Automotive hookup wire is not made for high voltage and must not be used here.
  • Screws, nuts, washers #2
    • This is what I used to mount the display.  It is probably designed for metric screws.
    • The kit comes with standoffs for use between the display and interface board.  I used nylon washers to stand the interface board off the mounting plate.
  • Screws, nuts, washers #4
    • For mounting the controller.  Be very careful that none of the hardware touches components or traces on the controller board.  There is not really as much clearance on the board as there should be.
  • Screws, nuts, washers #6, #8, #10
    • For mounting fuseholder, relays, and grounding strip.
    • For mounting acrylic sheet to bottom of box
Total cost about $500.

  • The quantities for the Quick Connects from Digikey are the quantities actually used.  Make sure you get extras.

Step 3: Mounting the Components in the Box

I used a 0.20" acrylic sheet as the mounting plate, primarily because the mounting plate for the box was out of stock.  I like the look of the acrylic.  But working with it is not fun.  Specifically, cutting it is a pain.  I had poor luck with the cutter made for it.  I think 0.20" is too thick for the cutter.  I ended up using a Dremel to cut part way through then broke it along the line.  I used a fine tooth hacksaw to cut the corner notches.

When drilling the acrylic start with small drill, no larger than 1/8".  Gradually increase the hole size, one drill size at a time.  If you make too large a step you'll crack the sheet.

I used washers to avoid scratching and possibly cracking the acrylic.

Step 4: The Cables

Make sure to use appropriate cable glands and tighten them securely.  These are what will protect the cables from being pulled out of the box, which could be dangerous.

Note that the common lead of the dryer cord is not used.  I insulated it with clear heat-shrink tubing.

There are eight quick-connect connectors that carry the full charging current (the connectors on the red and black wires).  It's very important that these are tight and secure.  While the connectors are made to be crimped on I didn't trust just the crimp.  After they were crimped I soldered them.  This requires removing the insulation and replacing it with heat-shrink tubing after the connector is soldered.  This soldering requires a substantial soldering iron to heat the 10 gauge wire.

If the connectors are loose on the posts the connections will heat during charging, possibly damaging components or arcing.  So make sure when you connect them there is plenty of resistance.  If they slide on too easily use a pair of pliers to tighten the connection.  If you can't get a tight connection it may be necessary to replace the connector.

The blue wire in the J1772 cable is not used.  It should be either cut short or coiled out of the way.

Step 5: Wiring 1

The yellow wires going up the left side of the box are high voltage (240V).  The ones going up the right are low voltage (12V or less).  It probably would be a good idea to use different colors for high and low voltage.  I understand there is a standard to use red for line voltage and blue for low.  I used AWG 20 hookup wire but AWG 18 is a bit more substantial and would probably be a better choice.

There are connections from the relay outputs to the controller board.  I chose to simply include those wires in the same connectors with the J1772 wires.  Another way to do it would be to use splitters to turn each relay terminal into two terminals.  Of course doing that adds two more connectors in the high current circuit, which may not be a good idea.  You decide which you think is best.

The pilot (orange) wire from the J1772 cable extends quite a bit further into the box than the rest of the wires from that cable.  I chose to extend the wire rather than stripping the cable back and cutting the other wires shorter.  It's a bit hard to see in the picture but the junction between the orange and yellow wires is covered with clear heat-shrink tubing.

For some reason the connection on the controller board from the GFI (Ground Fault Interrupter) coil is a pair of .025" square posts instead of the screw terminals used for the rest of the wire connections.  I soldered the wires directly to the terminals because I didn't have a mating connector.  A connector would be better if you can find one.  If you solder them you should add heat-shrink tubing as a strain relief.  I don't currently have that but will be adding it.

You really don't want to take a chance on those wires breaking off.  If one were to break off you would get no indication that there was a problem but the GFI wouldn't work.  Not a good situation.

Step 6: Wiring 2

There is a AWG 20 wire that connects the controller board to the ground bar.  The problem is that the ground bar isn't made to clamp down on an AWG 20 wire.  One way to handle this is to crimp a connector on to the wire then remove all of the connector except the metallic part that is crimped to the wire.  Another is to strip a long piece of insulation off the wire and fold the uninsulated part of the wire back on itself a number of times to make it thick enough to be gripped by the screw in the grounding bar.  Again, you decide.

Step 7: Wiring 3

Note the four-color wire connecting the controller to the display.  I could find no documentation describing the orientation of the cable.  As this cable carries power and ground to the display it's very important to get the orientation right so as to not risk destroying the display.  Please note carefully the orientation in the picture of the red and green wires on both connectors.

I chose to mount the pushbutton on the side of the box rather than putting it on the front as most implementations of OpenEVSE do.  As well as making the wiring easier, I prefer the button to be more out of the way as it is rarely used.  I would have used the Adafruit button but I was placing a Digikey order anyway and it was easier to just get a button from them.

Step 8: Testing

There are two functions of the EVSE that should be tested, the pilot signal and the GFI.

There are two aspects of the pilot signal that can be tested.  One is the duty cycle that tells the vehicle how much current it can draw.  This can be done simply if you have a DVM that measures frequency and duty cycle (such as the Radio Shack 2200075).  When in the EV Connected state (state B) the pilot signal should be 1.000 kHz with a 40% duty cycle (assuming the EVSE current is set to its default value of 24A).

The other aspect of the pilot signal that can (and should) be tested in the EVSE's response to a simulated EV connection.  This can be done with a 5Kohm pot and a diode (also available from Radio Shack).  For safety reasons I would extend the pilot and ground signals out of the box so you won't be near high voltage during the test.  Initially connect the pot directly between pilot and ground.  Set the pot to maximum resistance and energize the EVSE.  Now slowly decrease the pot's resistance.  At some point the display should turn red and indicate a diode check failure.

Next insert the diode between pilot and the pot with the anode connected to pilot and the cathode connected to the pot.  Again set the pot to its maximum resistance and energize the EVSE.  Gradually decrease the resistance of the pot.  At some point the display should change from EV Not Connected to EV Connected.  This is the point to test the frequency and duty cycle of the pilot signal if you have a multimeter that can do that.  Then continue decreasing the resistance.  The display should change from EV Connected to Charging and the relays should energize.  If you continue decreasing the resistance relays should de-energize and the display should change to Vent Failure.

The final test that should be done on the EVSE is testing the Ground Fault Interrupter.  This is done by putting the EVSE into a charging state and connecting a small load between ground and one of the J1772 power leads.  As this involves working with live power wires I am not going to try to describe how to do it safely.  Just remember that getting across these wires can make you really dead really fast.

While it's important to test the GFI functionality it's also critically important to do it safely.  So don't rush it.  Figure out a system that will let you test it without the risk of touching a live power line.