3.3 kW per hour or total?

Discussion in 'Prime Main Forum (2017-Current)' started by btrflies, Sep 2, 2017.

  1. btrflies

    btrflies Junior Member

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    There seems to be much confusion regarding how much electricity it takes to charge the Prius Prime. According to the Toyota website's FAQ:

    Q: "How much power does it take to charge the Prius Prime "

    A: "Prime uses less than 3.3 kW to charge with a wall-mounted level 2 charger, which is roughly equivalent to powering a small, residential air-conditioning unit. Using the included charging cable requires much less power."

    But my question is, does it use 3.3 kW every hour to charge? Or is it a TOTAL of 3.3 kW to charge from a completely depleted battery to fully charged.

    If it uses 3.3kW each hour and it takes 5.5 hours to charge from a home 120v outlet, then it uses from complete depletion to full charge: 3.3kW x 5.5 hours = 18.18 kW

    But if it's a total of 3.3kW from complete depletion to full charge then it only uses 3.3kW
     
  2. bisco

    bisco cookie crumbler

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    level 2 charger = 240v = 2 hour charge.

    3.3kw x 2 hours = 6.6kwh. plus charging losses.
     
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  3. priuscatprimeguy

    priuscatprimeguy Senior Member

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    Get one of these, then you will know how much you're using.

    [​IMG]
     
  4. priuscatprimeguy

    priuscatprimeguy Senior Member

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  5. priuscatprimeguy

    priuscatprimeguy Senior Member

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    when I'm charging my Prime using my Level 1 EVSE. The voltage is around 107 VAC and the current is around 11.5 amps. and it takes about 5 hours and ten minutes to charge from a "dead" battery (approximately 0.1 Miles EV) so..... 107 vac times 11.5 amps equals 1230.5 watts times 5 hours and ten minutes (5.1) 6.27555 KW:D
     
  6. Elektroingenieur

    Elektroingenieur Senior Member

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    There also seems to be confusion here about energy (work) and power, two different but related physical quantities. Energy—expressed in units such as joules (J), kilowatt-hours (kWh), or kilocalories (kcal)—is the capacity to do work. Power—expressed in units such as watts (W), kilowatts (kW), or horsepower (hp)—is the time rate at which work is done or energy is delivered or converted. One watt is one joule per second, and 1 kWh is the energy delivered or converted in one hour at a constant rate of 1 kW.
    Perhaps we should try that again:

    107 volts (AC, RMS) × 11.5 amperes = 1230.5 volt-amperes
    Assuming a resistive load: 1230.5 volt-amperes = 1230.5 watts
    5 hours + 10 minutes = 5 hours + (10 minutes/60 minutes) = 5.1666... hours
    1230.5 watts × 5.1666... hours = 6357.58333... watt-hours = 6.35758333... kilowatt-hours
    Rounding to three significant figures: 6.36 kilowatt-hours

    ...or in the units that matter, about $1.50, if you’re on an electrical tariff like mine.
     
  7. priuscatprimeguy

    priuscatprimeguy Senior Member

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    Yeah, I wasn't exact, but you get the gist of it.:D
     
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  8. Oniki

    Oniki Active Member

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    No confusion once you understand the units involved.

    kW is a rate
    kWh is an amount. The unit deconstructs into kW * h

    rate * time = amount


    ---

    You cannot say anything about amount if you only know the rate. You need time.

    Exercise:
    One car charges at 3 kW for 3 hours.
    Another car charges at 1.5 kW for 6 hours

    Which car took more energy (an amount) ?

    ---
    When the units make sense to you, your question will not.
     
    #8 Oniki, Sep 2, 2017
    Last edited: Sep 3, 2017
  9. drysider

    drysider Active Member

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    A battery stores energy. Power comes into play when you take energy out over a certain time period. If you have 3.3 kw-h of energy stored in a battery, you can take it out over 10 hrs., getting (3300w-hrs.) divided by (10 hrs.) giving you 330 watts of power, or you can take it out in 5 seconds, getting (3.3 kw-hrs.) times (3600 secs. in an hour) divided by 5 secs .for a total of 2.3 megawatts of power. This, of course, also results in fire, explosion, and disaster. The battery would probably disassemble itself before the whole 2.3 megawatts was disbursed. Note that the energy is the same in both cases. Hence, the difference between power and energy.
     
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  10. bisco

    bisco cookie crumbler

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    the total will also differ a bit, based on the starting level.
     
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  11. Lee Jay

    Lee Jay Senior Member

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    The car can absorb between 6.3kWh and 6.6kWh of wall-energy, depending on starting level, temperature, and charging rate.

    It can absorb this power at a rate between a little under 1kW (L1 at 8A) and a little over 3.6kW (240V at 16A). In reality, when you set the car to 16A, it maxes out about 15.1A, the same as when you use the provided 12A charger, it maxes out around 11.2A. 240V * 15.1A = 3,624VA which equals 3,624W if the power factor is unity (current is perfectly in phase with voltage). I've actually seen it a bit over 3.6kW:

    upload_2017-9-3_9-58-22.png
     
    #11 Lee Jay, Sep 3, 2017
    Last edited: Sep 3, 2017
  12. GT4Prius

    GT4Prius Active Member

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    According to my intelligent 240v UK charger that reports power usage to a private website for me, my charges have been 6.3 kWh once, 6.2kwh twice and all other full charges no more than 6.1 kWh. (Cost to me is less than Gbp 0.06 at night rate).

    Posted via the PriusChat mobile app.
     
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  13. heiwa

    heiwa Active Member

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  14. scm2000

    scm2000 Active Member

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    I have measured an average of 6.8kwh to fill the prime battery on the supplied L1 charging cable.
     
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  15. CharlesH

    CharlesH CA HOV Decal #5 on former PiP

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    Since that is measured from the wall, that includes overhead in the charging process. As I understand it, 120V charging can be expected to have a bit more overhead than 240V charging, if for no other reason than the charging process lasts twice as long, incurring more overhead from essentially fixed loads such powering the charger control circuits in the car, power conversion (AC has to be converted to DC at the proper voltage), cooling fans, and such.
     
  16. scm2000

    scm2000 Active Member

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    Yes and if you want to compute your actual cost per EV mile you use kwh measured at the wall outlet so your costs include the overhead/losses
     
  17. jerrymildred

    jerrymildred Senior Member

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    What he said. Don't confuse kW with kWh. When you say it will take 3.3 kW, that means 3,300 watts. If you do that for one hour, you've put 3.3kWh into your battery. If you do it for 2 hours, you'd put 6.6kWh into it.

    Using a water analogy, 3.3 gallons per hour (gph) is a rate of flow analogous to kW. If you put 3.3 gph into a big enough bucket for one hour, you'll get 3.3 gallons (analogous to kWh) in the bucket.
     
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  18. bisco

    bisco cookie crumbler

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    like this?:cool:
     
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  19. jerrymildred

    jerrymildred Senior Member

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    zactly! ;)
     
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