Well, I've been charging this off the medium-lame 120v cord they supply with the car. It works, and has two charge rates you can set - but you have to plug and unplug the car to make it respond to the button on the panel (lame). At least you can switch the AC into it on and off to get a sort of bang-bang control. But it's slow. Unless you cheat, the most you can force the car to hold a charge is 45% or so in mountain mode, which leaves about 55% to be provided by the house. With the 120v cord, this takes minimum of about 10 hours - longer than the sun is up, and around here, we don't burn a lotta KWH after dark.
The limit on 120v is set by the car electronics (more below). So I wanted to go to 240v, where the car will eat up to 3.3 kw. Two possible paths here - one is to just buy an EVSE cord and add the required logic, or buy the Voltec unit from SPX (a division of GM) and use that, lame as it also is. I did both because I wanted something quick now - and might be working up a hack for the Voltec unit so I needed one, and I also want a super tweaker standalone unit to use here long term (I'll sell one of these and keep the other).
I got the Voltec installed in about an hour - no big deal, just pulling some wire mainly, and hooked it to the new Xantrex XW 4024 inverter I bought to do this with, so my house inverter won't be stressed - this is most of one of these all by itself at max rate. The bonus is when not charging the car, I get 240v at 4kw average, or twice that peak, to run my lathe, welders, and fusor.
These units are kind of expensive. The GM Voltec is by far the cheapest at "only" $515 delivered - people tend to pay about $2k to have them installed, even with subsidies, as they just mark up a local electrician until the subsidy is gone, plus about another thousand bucks or so - it's not a not for profit outfit. You'd think you get a buncha fancy stuff for that 5 bills, but here's what you actually do get:
In a big plastic box, you get this little circuit board that's mostly blank. Fuses, then a GFCI sensor, a little +/- 12v power supply to run a uP, and a couple relays to switch power out to the car. It comes with a long coiled (ugh) cord that puts way too much side-stress on the car connector for my taste as well.
It turns out, that's all you need, and even a uP is kind of overkill for this. Sure, since they have it, they check AC frequency and voltage and a bunch of other stuff and refuse to work if anythings not perfect, but so what - the car doesn't care, it's just a brute force rectify and switch into the batteries kind of thing at the other end. After all, they don't have to change the car for 208v (between two phases of 3 phase) or UK, at 50 hz and whatever - it's just a universal switcher in the car.
Now, there's a pretty simple protocol involved, that uses only one wire and a ground return, and this is where the factory units are lame, and mine will be much better. Basically, the "cord" emits a 1khz +/- 12v square wave with a 1k series impedance. The duty cycle high is what the car uses to decide how much power it can draw (within the car own limits). It works like this. The EVSE (glorified extension cord) makes this signal all the time. When you plug in the car, the car has a 2.7k load hardwired so the cord can tell there's a car there. This load is through a diode - it only affects the positive part of the wave swing. When the car is ready to accept charge, it switches more load across the pilot signal - net about 880 ohms - to drop the pilot positive peak to around 6v. At this point the cord goes into action and closes the relays that let line power go out to the car. The unit could
vary the duty cycle to allow the car to adapt to varying amounts of power being available, in a situation like my solar system - but the factory ones don't have any way to do that. The unit could also switch the AC off when there's a need to conserve power for a bang-bang algorithm, but again, not the factory ones. I put a switch in the line to the 120v one so I could do this, but then had to defeat the car alarm going off for "charge cable theft". It still beeps once when power is restored. Not a problem here, but some places people whine about the fan and pump noises the car makes when charging, so you know they're going ballistic about a horn.
My home solar stuff uses a CAN Bus to talk to itself, and be controlled by. Xantrex makes a very lame "gateway" to the ethernet for the system, but the one I have is also very lame, and also broken in various ways as far as a I can tell, and does not allow ethernet to control the solar stuff - like I said, lame.
Thus are all slick projects born. As mentioned above, I bought one of these expensive cords, raw, to implement my own system for this:
Got this nice orange one from http://www.tucsonev.com/
This uses straight wire (which I prefer) and this one's number 8 stuff - not number 12, so less losses at 15 amps. It's longer than the Voltec/SPX unit and obviously much better made. The only difference is it lacks the built in led flashlight on the end, but has a connector cap to keep mud out (important here). There is an open EVSE project out there that uses an arduino to control this, but I like PICs, and theirs also doesn't have the desired/required features (though I could probably add them if I wanted to bother to learn the ins and outs of yet another UP). Here's their page - I've asked them a few questions, and they've helped with answers. I plan to publish this there and here as well - the more open source ways there are, the better. http://code.google.com/p/open-evse/
Today, I ordered a CAN bus development board, and an easylynx ethernet/webserver board to make this project design off of. The idea is that this will tie into - and control doggone it - all the Xantrex stuff. It will be able to also see all the internals of the solar system so it can know when there's spare power. It will also control the car charger - it will be a versatile EVSE station. It will emit a web site on my network that I can use to control it all from my couch if I want to, or just watch it all happen. It will also allow me to log it all on a PC somewhere on the network to have some nice stats on what the entire mess is doing and has been doing. This is a little bit of overkill of course - the dev boards have way more capability than this actually requires...and here's the kicker - the total cost for both - with programmers and a spare ethernet board - was under $300 - and comes with source code for the CCS compiler I have already. If I just redo the layouts - this will cost perhaps $50 plus the fancy EV cord, tops, yet have much more capability than what you pay $500-$2000 for (yes, some other manufs - including Xantrex/Schneider, sell EV cables that cost that much, even though there's diddly squat in one). Mine will use NOS solid state 40 amp relays, far nicer and safer than the cheezy potter-brumfield ones in the official units - you wonder how long those will live running at 90% of their ratings... It will monitor AC, it's own temperature, the allowed and actual car draw, the system battery voltage and net amperes, you name it (anything the Xantrex stuff already measures plus whatever else I feel like adding).
There is a non official volt forum I've been posting on a lot lately. There are a few people there who are really drooling for this - they have solar systems too....so I'll have no trouble selling any spares, though I doubt I sell a lot of these - not many people have off grid solar systems AND a Volt (or leaf or tesla or...). But I was surprised that there are about 6 on that board who are interested and actively asking me when they can buy one. So off I go on this. I wanted more control over the solar system anyway, and Dave Knight found an old copy of the Xantrex protocol to work off, so I should be able to replace a few hundred bucks worth of manual system control panels along the way, inside this same project. This is going to be nice! CAN bus looks like fun, that is, since CCS provides drivers for PICs that have the hardware, and also for external chips, that handle all the ugly parts of a shared-wire protocol. All you have to do is figure out what you want to do at that point.
Here's the CCS stuff I got to work with. Looks like some fun is in store.http://www.ezweblynx.com/product_info.p ... WEBLYNX_5K
For the ethernet interface - and you get a spare one along with a programmer and code for the price.
And here's the can bus stuff - way overkill, two cpus and a couple expanders so it's a whole network by itself to play with. I plan to just grab the design for this project - any pic can do this with the interface chip - maybe even the ez web lynx one...but I wanted to make the learning curve as short as possible so as to get back to science here.http://www.ccsinfo.com/product_info.php ... =CANbuskit
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.