Monday, February 17, 2014

Metering the EV

A few years ago, I blogged this on MNL, but due to some sort of something or another, the blogs were removed and I missed the chance to migrate them so I am recreating this one since I have had a lot of interest in this subject lately.

3 years ago when I first got my 2011, I charged at 120 volts for 2 months or so because I was getting ready to move (move was required due to owner wanting to sell) and did not want to put anything in there.

So I was using the Kill a Watt meter and found that I was averaging right around 75% "well to wheels" efficiency using the miles/ kwh meter on the dash of  the LEAF for my "battery to wheels" numbers.  This in essence measures charging losses only since there is loss in every step of energy transfer process and yes, this banks on the dash calculation being accurate and that in itself is dicey but at least its not Carwings!  :)

After the move and getting settled in, I was investigating 240 volt meters and found nothing in the range I was willing to pay for until Tom Saxton a Pacific Northwest EV enthusiast turned me onto his method which was to simply to install my own meter!

I started by going online to   then mousing over "products" at the top of the page and clicking on single phase remanufactured meters in the drop down menu.   There I selected the "EZ Read FM2S 200A 240V 3W Meter"  which was $17.50.  This meter requires a base plate which was another $10.50.  Shipping/taxes, etc.  added another $15 so $$ invested; $43.45

Went to store to purchase some random parts for another $11 and  simply disconnected my plug, installed the meter, and then ran wire from the meter to a new plug box.

Now I did get Phil's EVSE upgrade so it took my 120 volt, 12 amp EVSE to 12 amps, 240 volts. This was the only option at the time I got it. Later, I got another upgrade which was MUCH better.  

Charging at 12 amps kicked my efficiency up to about 83%. The biggest reason for this is the static load used for water circulation, monitoring, etc. that runs during charging. It varies little between 120 volt charging and 240 volt charging. 
For 2011/12 LEAF users charging at 240 volts, 16 amps, most were reporting efficiencies in the 86-87% range.

Now the meter is not highly accurate for single trips and I only entered in whole digits but over time its accurate enough. It is a "utility grade" meter and guaranteed 99.95% accurate (as if I could tell the difference?)

When I got my 2013 LEAF, I did the EVSE upgrade again but this time, my EVSE was programmable so I set it to run at 20 amps @ 240 volts moving my efficiency to 90%  and reducing my full charge time from about 8 hours to 3½. 

I also ran several experiments trying to determine my fast charge efficiency and have gathered some numbers but all have been during Winter so will hold judgement until I can run some numbers during Summer but so far its looking like 95+% is a probably a pretty close guess.

So if you are not satisfied with estimating your electrical usage with the efficiencies I mentioned above and you want a reasonably cheap, easy way to do it that is accurate. Here is your $54 solution.

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