Assembling the Electric Motor Werks Open Source Level 2 Charging Station (basic kit)
My wife just got a Chevy Volt, and, even though we don't really need it, I wanted to put in a 220 V Level 2 charging station because I think they are cool and may become an asset for the house over time. These units are formally called Electric Vehicle Service Equipment (EVSE) and all that is in one of these babies is a microcontroller (and its power supply) to talk to the car, and a relay to turn the juice on and off.
Unfortunately, the commercial offerings are something of a racket -- they charge $600 to $1000+ for the hardware alone. By the time you've run a circuit and permitted the thing, you can wind up paying $2000, which seemed nuts to me. So I looked for other options.
There is an open EVSE project that has plans and boards and info so you can build your own unit, but this involves a lot of component gathering I didn't really want to do. Fortunately, the good folks at Electric Motor Werks ran a Kickstarter campaign in the Fall of 2013 to put together a full open-source/open-hardware kit. This campaign was a big success, so by the time I ambled in (late to the party, as usual) the kits were in stock and available. Further, by now (Jan 2014), the kit came with the main board already stuffed and the microcontroller (an Arduino) programmed, so it was just a matter of assembling the thing.
The kit was $150, the cable with plug that connects the EVSE to the car was another $150 (ouch!), and wire, circuit breakers and misc were another $150 -- with the circuit wire being most of that. So I am in for about $450. But, judicious use of a Christmas gift card brings my out of pocket to $350, and I have about $50 worth of extra wire I'll probably sell.
Anyway, the first thing to do was put in a 220V circuit. I went with 40 amps, as that will support a 30 amp continuous load (with a 1.25 load factor). I ran AWG 8/2 NMB wire from the panel to the garage. Now, the Volt has puny 16 amp charger on board so a Juice Box configured for 30 amps won't be breaking a sweat, but a lot of current (see what I did there?) cars already have 30 amp chargers on baord, and that is going up to 40 or more in some models. So, 30 amps is a future-proofing compromise. While it may wind up being a mere trickle charger for a Tesla Model S (with its 85 KW battery), it will do most all-electric cars overnight, and the Chevy Volt in just 4 hours. (Plus, going with 30 amps saved me from having to run #6 wire, which would have been a big PITA.)
You can click on all of these pictures to embiggen.
The new supply circuit emerges:
The first step was to modify the case to take a liquid-tight conduit connector since I intended to hard-wire the unit. I'm also flipping around the input and output holes because that works better with my set up. I was worried about room in the box doing this, but it worked out fine.
Next step is soldering the power supply to the main board.
Then adding wires to tap signals and control the relay. I added lugs of my own to all the wires becuase I'm anal that way.
Next, I mounted the board, power supply and relay in the case.
The 220 V supply circuit is brought in and connected to the relay input terminals (and the ground screw). If I had built the kit as intended, the power would have come in on the left. But making the jog over from the right didn't cause much trouble.
Next I prepared the wires on the end of the (expensive) output cable with the magic J1772 nozzle on the end. This cord is just two hots and a ground, plus a "pilot" signal wire on pin 4 that gets connected to the main board in the Juice Box so the micrcontroller and car can talk to each other (by changing the duty cycle and amplitude of a 1 KHZ square wave). There is also a "proximity" pin, which is connected to a voltage divider in the handle between that pin and ground, so the car can stick juice on it and detect when the nozzle is present.
I can hardly wait until theives start cutting these cords off and selling them for quick cash!
Here the output cable is brought into the box and connected. The black ring on the main board the wires go through is an inductive current sensor which is used for GFCI protection. I mashed all the lugs on the input and output wires in a vice, so got a super good connection. I then covered most of the metal in shrink tubing.
I wanted the wires to go through the middle of the current sensor ring exactly in the center and exactly at a right angle, so I made this elaborate jig of string and clamps to get it positioned just so. (Hey, I'm not proud!)
I then filled the center hole with RTV silicone rubber that I trowled in with a screwdriver. I let it sit for 24 hours.
The final product:
Time for a temporary lash-up to see if it works:
Check for output power....YOWZA! We're in business!
Proper operation confirmed, the Juice Box is attached to the wall. I put some feet on the back to keep it out from the wall surface a little bit.
Last thing to do is to stick on the label...(As configured, my max output power is only 7.5 KW)
And do the final wiring...attach cover... ( BTW, the supply circuit is not coming from the service panel you see in this picture, but from the other side of the house -- long story.)
Mmmmm. Delicious juice.
All done. (Though I'm going to put in a cable/hose hanger to get the output line off the ground.)
And I did, in fact, get a nice hose hanger from Blue Mule products...
This was a fun kit. The instructions aren't that great, but the assembley isn't hard, and there is a YouTube video. I hope EMW takes the time to do a proper assembley manual like the ones Elecraft does (the gold standard) -- I'm sure it will save them a lot of support costs. Other than that, I'm happy to he charging at 220 V and anxious to see if this thing burns the house down or what.
Edited 25 Jan 2014.