Measuring the Total Energy Consumption of Your EV Part 1 – Tezco’s Homebrew Energy Monitoring and Data Logging Device In the following posts I’m going to describe how I built a data logging system to measure my EV energy consumption. Other posts have described monitoring systems using TED – The Energy Detective; however, TED relies on data transmission through your home’s wiring (aka PCC – Powerline Carrier Communication). PCC has it’s drawbacks including sketchy transmission over long distances, interference from on-line noise, and attenuation when noise filters are on the same line. Since my garage is detached and several hundred feet away from my main breaker panel, and my home office power is heavily damped due to large UPS’s, I first took at look at the TED forums and read about the difficulties that some users had with TED in similar situations. I also wanted to monitor temperature readings in my garage, so I decided to take a road less traveled. Next – Data Summaries Part 2 – Data Summaries I'll edit this section from time to time to show some of the data that I have collected. Revised 02-15-13: Data points on the following graph show the energy consumption (normalized to idle energy loss per 24 hrs) of the car when it sits parked in the garage, referenced against the ambient garage temperature about 8" off the floor (ie at battery pack level). The pink square represented the night the car upgraded to v4.2 (no significant increase in energy use, despite all the bells and whistles that go off during updates). Note that my firmware versions never have included active sleep mode. It appears that there is more loss at colder temperatures (or perhaps it takes more energy to keep the pack at proper charging temp during the charging cycle?). There is a moderate scatter of data points which suggests that the SOC at the end of each top-off cycle may vary somewhat. Next – Assembly of the Data Logger Part 3 – Assembly of the Data Logger My system is built with components that are available online from Onset Computer Corporation, as well as miscellaneous hardware items that can be purchased at Home Depot and your local hardware store. The system uses a data logger which locally records four channels of information. The data sampling rate can be set by the user, and can be as short as every second. The logger holds 43,000 readings (which is about 7.5 days worth of four channel logging, when set to sample once a minute). The data in the logger can be downloaded via a USB cable to a laptop or a data shuttle, or you can unplug the logger and bring it over to your PC. Since my logger is mounted inside a junction box, I didn’t want to have to turn off the power to open the box to access it or to physically take out the logger so I decided to go with the data shuttle. Initializing the logger does require that you connect the logger and it’s attached sensors to a computer which is running the HOBOware Pro software. Since the license is for one computer only and I wanted to run the software on my PC, I decided to make my whole setup mobile, so I could bring it in to the computer for initialization. Therefore, my device has a plug on one end, and a receptacle on the other. I just unplug the EVSE from the wall, and insert the box in-between. The HOBO logger’s Li button battery is good for about a year, but the life is shortened at low temperatures. I’ve put a nightlight in the box, and monitor the interior temperature with the 1 foot temperature probe. The other 6 foot probe hangs down out of the box and is held about 6 inches off the garage floor, to approximate the air temperature at the level of the Tesla battery pack. The main components purchased were: (see http://www.onsetcomp.com/products/data-loggers/u12-006 ) U12-006 (HOBO U12 4-External Channel Data Logger) BHW-PRO-CD (HOBOware Pro Software) Cable 4-20MA (Connects voltage sensor to logger) CTV-B (0 - 50 Amp split-core AC current sensor) TMC1-HD (Air/Water/Soil Temp Sensor -- 1' cable) TMC6-HD (Air/Water/Soil Temp Sensor -- 6' cable) U-DT-1 (HOBO U-Shuttle) Disclaimer I’m not a licensed electrician, so I can’t vouch for the Code compliance of my system. Certain aspects are not up to code; for example, I clamped the voltage monitoring leads into the output receptacle using the same clamps that hold the main power leads. My garage also had an old NEMA 10-50 outlet that I use for welding. This is code compliant when used for 240V with two hot leads and a neutral, but mine was wired with a ground instead of the neutral. Fortunately this works with the GFI needs of the AV EVSE that I use for charging. You might want to use more a modern NEMA 14-50 for example, and might want to purchase a higher amperage split core sensor if you are thinking of charging at more than 50 amps in the future. Next – Photo of the Parts, Pre Assembly - - - Updated - - - Part 4 – Photo of the Parts, Pre Assembly I purchased a Raintight junction box and drilled out a 2 1/8 inch hole on the side for the outlet receptacle using my drill press and some oil drizzled on for cooling during cutting. The wooden plywood block is used to mount the Data Logger, such that cold from the box wasn’t transmitted to the logger, and the light bulb is used to keep the logger warm during the winter. The four plates with the tabs are flush mount hangers which make it easy to pull the box off the wall for the logger’s initial startup, or re-initialization should the battery fail. (The shuttle can normally power the logger while you replace the battery (which preserves the initialization settings), another plus for buying the shuttle.) Next – Photo, Partial Assembly - - - Updated - - - Part 5 – Partial Assembly The major parts are now installed. Voltage sensor is on the left, current clamp on one leg of the mains, and heater light bulb on the right. Next – Photo of Assembled Device - - - Updated - - - Part 6 – Photo of Assembled Device The Logger is installed. Exiting the box thru a grommet bushing behind the wood block is a the USB cable (to be used when I plug in the data shuttle), the long temperature probe, and a lamp cord that connects to the nightlight. The cord is plugged into a nearby 120V receptacle in the winter to keep the logger toasty. Might have to move up to a 7 watt bulb if this cold weather continues…. Next – Initial Plot - - - Updated - - - Part 7 – Initial Plot Here is my first data. Downloaded from the logger to the shuttle, sent over to the home PC via sneaker net and uploaded to the HOBOware Pro software package. This software includes some statistical subsets that can, for example, analyze the 10 hour window I have drawn between the vertical black lines which shows the mean temperature near the garage floor was 28.5 degrees (Solid green line). (You can see a few squiggles in that line: Negative blip when I went in and out of the door, and positive blips when the heat turns on (set to come on at 34 degrees, but stays colder at the floor.) The dashed green line is the temp inside the box, which fell from 70 degrees and finally stabilized around 40 degrees overnight. The solid black line measures the amps sent to the EVSE and Model S, and the blue line, the voltage. I had the S unplugged for a couple of days, so the 2-hour charge shows just how much the “vampire” load is (still waiting for the 4.0 or 4.1 or 4.2 update, so currently no display sleep mode in my S). ps Has anybody measured the power factor of the charging system, so I can calculate the actual kW?