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Has Anyone Metered Their EV Outlet?

Discussion in 'Model S: Battery & Charging' started by mknox, Oct 12, 2012.

  1. mknox

    mknox Well-Known Member

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    So I'm a bit of a home automation geek and have several of my electrical circuits individually metered (via CTs in the electrical panel). I obviously plan to do so with my NEMA 14-50 that is going into the garage.

    Has anyone else done this and, if so, do you have any insights into the amount of electricity you use vs. miles driven?

    I had my company Volt at home for a week or so, and metered the 120 volt outlet it was plugged in to. Of particular interest to me was the amount of electricity being consumed by the car after it was fully charged. From time to time, you could hear pumps, fans and other gizmos running, and the power consumption would vary anywhere from 50 to 300 watts.

    What this translates to is that the amount of electricity coming out of the wall is somewhat more than what ultimately comes back out of the battery to the traction motor. This "phantom load" (think of your cell phone charger left plugged in after the phone is removed - on a much larger scale) adds up over time. I'm not particularly worried about this, but have an interest in understanding it. It's kind of like spilling gasoline (that you've paid for) at the pump every time you fill your ICE. The car's fuel economy computer wouldn't take into account this "spillage".

    Once I've had my car for a while, I'll be able to get a true picture of kWh's I've paid for vs. miles driven in order to see what my "real" Whs/mile are, but I'm curious to know if any current EV owners have done anything similar.
     
  2. vfx

    vfx Well-Known Member

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    Martin eberhard bought a meter on Eaby and put it on his charger circuit.
     
  3. markwj

    markwj Moderator, Asia Pacific

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    I've done it.

    The problem is that the Tesla Roadster charge history is so buggy that there is really no way to correlate the two.

    If someone asks me how much it costs to charge, I give the meter reading, not the car's reading.

    Note that after charging, for the Roadster at least, the car's pumps may be running but the electricity consumed is from the battery not the wall. This is seen as a gradual loss of range (meaning more must be put in next charge than used driving).
     
  4. Charged_Up

    Charged_Up Member

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    I installed a TED 5000 series meter on my electric outlet(s), but can't opine on usefulness as I don't yet have my car! However, I did test it and it is working well - internet based using powerline networking to go from the box to my router - and it stores years worth of data and can be used also to monitor other circuits or even whole house consumption.
     
  5. phx182flyer

    phx182flyer P11051

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    I would like to do the same thing, ie, meter the 14-50 I'm going to have installed in the garage. Any suggestions on the type/brand of meter?

    Thanks,
    Ron
     
  6. PRJIM

    PRJIM Member

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  7. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    I've got a TED on my sub-panel that only powers the Roadster HPC and the Model S 14-50 in the garage.

    I've done a couple of tests, and need to be more consistant recording data, and charging one car at a time, but it looks like there is a 15-20% overhead in what comes out of the panel compared to what the car reports going into the battery. Something like 2% of that is the 5V drop in line voltage when the 40 Amps is drawn. I need to take a digital volt meter down the line and see where the drops are, but it seems most of it is in the UMC. I have plugged into a 14-50 that is close to the 400 Amp panel in my barn and connected with a larger wire (it was originally wired for a 70A electric heater), and I got the same 5 V drop. The UMC cable also gets noticeably warm during charging, a trade-off for lightness; 40A*240V=192W over 20 feet of cable is almost 10W/foot. The other problem in the measurement is the quantization error caused by the power taken being only displayed in whole kWh, thus a 50 kWh charge has +/- 1% error, and a 10 kWh charge has a +/-5% error.

    I will try to log many charges and get a better estimate of the overhead.
     
  8. dpeilow

    dpeilow Moderator

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    I have as my garage is on a communal supply and thought it wouldn't go unnoticed ;)
     
  9. mknox

    mknox Well-Known Member

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    Thanks for the feedback. With the Volt, I noticed the instantaneous kW reading would vary with the pump sounds coming from the car and concluded that power was coming from the utility supply and not the battery. This would seem to make the most sense, because you wouldn't want your battery running down (even a little bit) when the car is actually plugged in.

    - - - Updated - - -

    Thanks! I'm using a TED myself. 15 to 20% is kind of where I thought it would be given losses in the chargers, voltage drops and "maintaining" the car while plugged in. I'm hoping to more than make up for these losses by mooching free charges at public stations, at work and so forth :)
     

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