I need to accurately record power consumed from charging. Suggestions?

Discussion in 'Prime Plug-in Charging' started by iregret, Mar 4, 2018.

  1. iregret

    iregret New Member

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    Hey guys, finally bought a 2017 Prius Prime yesterday. I am allowed to install a level 2 charger at home (it's own 40a dedicated circuit), but have to keep accurate track of power consumed so I can pay the bill. Right now, I'm leaning towards the Chargepoint level 2 hardwired charger. It's expensive, but the app keeps track of power consumed.

    I'm wondering though, I really need to spend that money.

    There's no discount on charging at night where I live, so charging slower at home everyday with the factory charger is probably fine. Is there a reliable accurate meter I can plug in line to the factory charger? If there isn't an elegant solution, I'm fine with buying the expensive one because it seems to review well other than the bright lights. Also, I'll be charging outside.

    I get to charge for free on campus, and campus is 25 miles away, so even if I didn't charge at home, I'd be alright.
     
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  2. Prodigyplace

    Prodigyplace Senior Member

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    @jerrymildred may have some ideas. He recently installed his charger with a meter.
     
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  3. ct89

    ct89 Active Member

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    How fancy a meter do you need...This is what I installed...Been working great for a couple of months now.

    DROK Digital AC Multimeter Voltmeter Ammeter 80-300V 0-100A Watt Power Energy Meter
    [​IMG]
     
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  4. Old Bear

    Old Bear Senior Member

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    Take a look at my post on this topic (and the related thread) here:
    watt-hour metering | PriusChat

    I have mounted one of these meters in a standard "two-gang" deep electrical box and installed it next to the circuit breaker panel. I haven't had it in operation long enough to be able to give it an accurate and detailed review, but it appears to be working for my application.

    Keep in mind that it can be reset by pushing a button, so it's not something that can be reliably audited.

    (There's nothing to prevent you from resetting it to zero in the middle of the month and claiming it was displaying a full month of use when your landlord comes to call. But, if you're honest and ethical -- and your landlord trusts you -- there might not be a problem.)
     
    #4 Old Bear, Mar 4, 2018
    Last edited: Mar 4, 2018
  5. jerrymildred

    jerrymildred Senior Member

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    I'm using this one:

    I verified it's amperage reading with my Klein clamp on meter and it matched. It was only $20. It only has one button, though, so resetting or programming is a little fussy. Works great, though.
     
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  6. Prodigyplace

    Prodigyplace Senior Member

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    Thanks, Jerry. I notice the display on Amazon shows usage in watt-hours.
    Electricity is normally billed in kilowatt-hours. 1000 watt-hours equals 1 kilowatt-hour.
     
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  7. Old Bear

    Old Bear Senior Member

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    The display shifts to kWh when the cumulative number of watt-hours exceeds the number of available digits in the display. Robin Mitchell noted in an earlier post in the other discussion thread:

    The energy display starts off in Wh, as shown in your photos at the top of this thread, and then switches to kWh once you overflow that. When I charged my car last night mine overflowed, and it went straight from showing watt-hours (i.e. a resolution of .001 kWh) to showing whole kWh (a resolution of 1 kWh). I had been hoping it would go through an intermediate phase of showing fractional kWh so that I could track individual charges with reasonable accuracy when I wanted to, but it looks like the only way to do that is to reset the energy display first and lose the accumulated count.

    In Robin's application this was a problem.... in your application, it's a feature!
     
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  8. padroo

    padroo Senior Member

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    Jerry, if you are charging at 240 V do you have two current coils to read amperage?
     
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  9. ct89

    ct89 Active Member

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    If you google "DROK Digital AC Multimeter Voltmeter Ammeter 80-300V 0-100A Watt Power Energy Meter" you will see an amazon page that provides some additional images...

    Here's one of the wiring diagrams...
    [​IMG]
    Shows that you only need to connect the sensor to one leg.
     
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  10. jdenenberg

    jdenenberg EE Professor

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    As long as you do not have a ground fault (A ground fault means that current is not going where is should, for example through you), the current in the two phases are equal (but in the opposite direction), so you only need one current transformer.

    JeffD
     
    #10 jdenenberg, Mar 5, 2018
    Last edited: Mar 5, 2018
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  11. Rmay635703

    Rmay635703 Senior Member

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  12. mczouav

    mczouav Junior Member

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    Perhaps an OpenEVSE charger is what you want. Super easy to assemble if you have a screwdriver. A lot cheaper than the commercial all made chargers and wifi configurable...Or if you want to use you L1 charger, an emoncms adapter to track power...

    Posted via the PriusChat mobile app.
     
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  13. jerrymildred

    jerrymildred Senior Member

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    No, just one since the current is the same on both legs as @jdenenberg mentioned.

    And, to confirm @Old Bear's comment, yes, it switches to kWh when it runs out of digits. And, even if it didn't switch, it's not a major effort to just move the decimal point. I'd actually prefer it to be more precise. For example, I reset mine when I get gas. It's now reading in watt hours because I just filled the tank. But before I reset it, it read 66 kWh. So, was it 66,002 watt hours or 66,989 watt hours, or what?
     
  14. Prodigyplace

    Prodigyplace Senior Member

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    Probably somewhere between 65,500 - 66,499 watt hours.
     
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  15. jerrymildred

    jerrymildred Senior Member

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    Could be. No idea what kind of rounding algorithm they use.
     
  16. iregret

    iregret New Member

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    Okay, this is more my style for sure!
     
  17. Sam Spade

    Sam Spade Senior Member

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    If you are talking about a multi-unit residential building, odds are that YOU are NOT allowed to do anything electrical yourself.

    When you hire an electrician to legally install the outlet, he can also install an approved meter.
     
  18. Old Bear

    Old Bear Senior Member

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    Actually, this kind of meter can be reset. That's why the version that many utility companies use are mounted with a ring and a tamper-evident seal.

    But, if you like the concept of a traditional electro-mechical watt-hour meter like the one Rmay suggests, then you will also need a meter base and some other stuff. You electrician will know what you need.

    Mechanical-watt-hour-meter.jpg meter-base.jpg

    This is a pretty hefty solution to a relatively small problem. The $20 digital meters other users have suggested -- or the choice of an EVSE unit which reports its own power consumption -- would be less costly and simpler.
     
    #18 Old Bear, Mar 5, 2018
    Last edited: Mar 5, 2018
  19. McRascal

    McRascal New Member

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    If you only need to connect the sensor to one leg, how does the meter know you're running 240 vs 120 volts?
     
  20. jerrymildred

    jerrymildred Senior Member

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    Look at the drawing. Voltage wires connect to both wires. Coil goes around one leg.
     
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