OpenEVSE - a DIY charge station


I'm not sure if it was the desire to save $500 or the more fundamental curiosity of “what's in the box?” that interested me in the OpenEVSE. No doubt I was motivated by both impulses as I researched options for charging my new Ford Focus Electric at the maximum rate. A 240v 6.6kW home charge station could give me a full charge in under 4 hours, compared to the 16 hours or so it took with the 120v 1.4kW charge cord provided with the car.

It would be so easy to browse the Amazon listings and simply one-click from the selection of name-brand Level 2 units. But it bugged me that most of the 240v home charge station options cost between $900 and $1,100. I knew from a bit of online research that the devices often called EV Chargers were really just sophisticated switches with cables and connectors. The EV charging cords properly known as EVSE, Electric Vehicle Supply Equipment, are extension cords that don't supply power to the end connector until after it's been plugged in and your car has indicated it is ready to accept current. The EVSE also tells the car, by a signal sent through a separate “pilot” wire, the maximum current it can deliver, so that your car doesn't overload the circuit and trip a breaker or worse.

Without diminishing the importance of this safety circuitry, or the ingenious design and careful planning that went into the now widespread standard for EV charging, this is fairly simple stuff as electronics go.

When I heard that you could build your own high-power 240 volt 30 amp EVSE from high-quality off-the-shelf parts and a couple of custom circuit boards created by an open source hardware collaborative, I was intrigued. I knew I would learn a lot more by hands-on assembly than simply reading the J1772 design specifications and looking at the wiring diagrams. The parts list posted on the OpenEVSE site estimated that all the parts, including a heavy-duty purpose-built steel enclosure, would cost about $500, saving me at least $500. The cost savings would be even greater if I were to add features like WiFi which made it equivalent to the EVSE units that ran into the $2,000 range.

One issue that gave me pause was the realization that the EVSE supplies high voltage and high currents – enough to kill you if mishandled. Even though I felt confident that I could avoid electrocuting myself – I am fairly handy with household repairs – it was still a little intimidating to take on a project that had the potential to fry some very expensive charging electronics in my car if I made a serious mistake in assembly.

So I became really interested when I read that Chris Howell, the lead developer of the OpenEVSE, would be hosting a half-day workshop in Alameda California to help folks assemble their projects. After a few clicks on the links posted in the parts manifest on the OpenEVSE Google code web site, my parts were on the way from the various electronics supply houses. An email to Chris and the “build day” reservation was booked.

The group of eight hopeful builders, and another dozen or so helpers and observers gathered around the improvised work benches at O'Connell Volvo, an independent repair shop that donated the meeting space. The gathering was typical of the assembly you might find at any EV club; middle aged and older working professionals, a few retirees. Most were technically savvy but not electrical engineers, just regular guys not afraid to fix stuff on their own when it breaks. I imagined that in the very early days of PC computing, meetings of the Homebrew Computer Club might have been like this.

Small groups formed around each table and started assembling the parts. Helpers from the East Bay Chapter of the Electric Auto Association, coordinated by club president Tom Keenan, were there to answer questions and offer advice.

The OpenEVSE units went together remarkably easily. Screw down the components on the enclosure mounting board with the plastic stand-offs. Cut a few wires to length, strip the ends, crimp connectors, attach after double-checking the right connect points. Install the mounting board in the enclosure with four machine screws. Mount the LCD display and push button switch on the cover. Install the wall cord and the heavy-duty cable with J1772 connector.

The assembly only took a few hours even for people who had never seen the insides of an EVSE before, myself included, and the pace was more geared toward socializing and learning than production efficiency. Although intrepid builders handy with a soldering iron can build their own controller circuit board, Chris Howell provides fully assembled boards and LCD displays. The assembly of an OpenEVSE unit is more of a mechanical task than an electrical fabrication. The entire job can be completed without the use of a soldering iron. Using a heat gun for shrink tubing is helpful and makes for a more professional looking result than using electrical tape.

As the assemblies were completed, Chris tested the units with a very professional-looking homemade test rig made by Scott Cornell, a member of the Electric Auto Association East Bay Chapter. Most worked properly immediately; a few were sent back to the bench for better crimp connections or minor wiring corrections. I had arrived a little late and didn't finish up my project in the shop, but was able to complete the project at home after some tips from Chris and other community members on the project's Google Groups forum.

Once my OpenEVSE project was complete and tested, I plugged it in to my 240v 30a circuit. The unit completed its self-test within seconds. I clicked through the setup menu to set max power draw, in this case 25 amps until I get my wiring upgraded from #10 to #8 AWG, which can handle the full 30a draw continuously.

Somewhat cautiously, I plugged the high-quality Leviton J1772 connector into my Focus Electric's charge port. No smoke. No sizzling. Nothing blew up. Just the tranquil pulsing glow of the Focus EV's lighted ring that indicates that the car is accepting a charge. The OpenEVSE's LCD status display confirmed the same. Although both car and charge station operated completely silently I swear I heard faint strains of the brass section intro of Aaron Copland's “Fanfare for the Common Man” emanate from the damn thing.

The unit has been in daily use for the past month and has worked flawlessly. The heavy duty steel enclosure and high quality cables give this unit every bit of the polish and professionalism of any commercial unit on the market. Support from Chris and the OpenEVSE community was quick and well informed. The project was so much fun I plan to build another one with my nephew some weekend this summer. I'll be contributing some assembly documentation to the OpenEVSE project soon, and you can expect more coverage on this web site as the OpenEVSE project continues to innovate and gain builders and contributors. Chalk up another success for the Open Source Hardware movement.

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