Thursday, March 5, 2015

Adventures in EV charging

2012 Chevy Volt

When I purchased my 2012 Chevy Volt, I was aware that it came with its own charging cable that could plug into any regular 120 V outlet, but it would take almost 9 hours to fully charge the vehicle.  Faster Level II chargers could reduce the full charge time to below 4 hours.

Since I wanted to track energy usage for charging the vehicle, I pulled some heavy wire (Romex 10/3) from a 20Amp 240V breaker out to the front of the building and installed a separate Watt meter that I found on eBay, and installed a 120V outlet below it to start with.  (I read the meter weekly and post results to a chart on my web page.)
Me installing Watt meter
With an EV range of 27 to 38 miles, I thought it would be convenient to install a 240V Level II charging station that could charge the vehicle in less than four hours so that I could make several long trips in a single day if needed.  In doing my research I found that most charging stations available sold for over $1000 and up into the several thousands not including installation.  But I found that GM was subsidizing a charging station made by Bosch called the Voltec SPX, and I purchased one for around $500.  Being an electrical engineer and DIY inclined, I installed the charging station myself.  I have learned that if you hire a contractor to do this it can cost anywhere from $300 to almost $2000 depending on how much wire they need to pull for this job.  

The installation was relatively simple:
Voltec SPX charging station and Watt meter
At the time I considered this charging station to be a piece of competent German engineering with a good balance of form and function.  The round shape allows you to hang the coiled charging cord onto it for storage and it appeared to work just fine.

The trouble began 11 months later just before the charging station went out of warranty.  It stopped working and showed a red indicator light.  So I returned it to Bosch and they sent a replacement.  When it failed again a few weeks later I decided to open it up and have a look inside.   What I found was that the engineer who had designed this charging station had installed fuses on the circuit board that were soldered into the board making them completely un-replaceable to your average consumer.  However, as an electrical engineer it was relatively simple for me to remove and replace those blown 15 amp fuses with ones rated for 20A.  The original fuses were rather conservatively rated since the Chevy Volt draws just below 15A per leg of the 240V line.   In retrospect I think that my 240V table saw creates power surges that more than likely caused these fuses to blow.   Here is a close-up of the circuit board inside the charging station:
Fuses in Voltec SPX charging station
I became quite irritated when my replacement fuses blew a few weeks later since it is a pain to open up the charger.  So I installed 2 small 20A circuit breakers on pigtails and sited them where I could reset them from the outside:
2 - 20A circuit breakers added to Voltec SPX charging station
This fix worked, and I was able to re-set the breakers every so often when they tripped.  But a few weeks ago the charger stopped working and displayed an ominous blinking red idiot light.  This time I had had it!  So I went back to charging from a 120V outlet using the Volt charger that came with the vehicle while I researched affordable options. 
Chevy Volt charger
What I found was an affordable open source EV charging station made by Electric Motor Werks Inc. in California.  These guys had developed their product with a Kickstarter campaign in July 2013 and now had a well-designed product on the market that I was able to purchase for under $500.  This clever design is based on the popular Arduino microcontroller and it contains a very basic 240V relay for transferring power to the vehicle.  It is built into a plain-vanilla sealed metal box that can be mounted indoors or outdoors.

I decided to install the charger inside and reuse the charger cable and plug from the original charging station.  Here it is installed inside behind the Watt meter:
JuiceBox charging station
I installed a small green light on the side of the box so I could tell when the charging station was providing power to my vehicle at a glance.

In addition to reusing the original coiled charging cord and plug, I also took the plug holder out of the old charging station and mounted it to the wall under my carport.  This allows me to charge and store the connector in 2 locations which is convenient.

Charge plug holder
This new setup works perfectly and I am pleased to own a piece of open source hardware that I know that I can fix or upgrade myself in the future should it be necessary.  I did require some tech support via email during the installation, and found the guys at Electric Motor Werks Inc. to be very responsive, friendly and helpful.

Here is my Volt being charged under the carport, and you can see the other charge plug storage location below and to the right of the Watt meter out front where I often charge the vehicle in good weather.  I also put a 120V outlet on the left of the meter box for the Volt Charger.
Chevy Volt charging under car port
Volt charging from JuiceBox (hidden inside building)

I hate to throw things in the garbage, so I am stripping out all of the parts that I can salvage from the original Voltec charging station including the circuit breakers I added, terminal strips, ribbon cable and even some screws.

Voltec SPX inside - mostly scrap.
Oh, did I mention that my Volt is charged from our 5.6kW solar array?  This means I am driving for free with zero carbon emissions for local driving most of the year.  More info can be found on my Chevy Volt web page.