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    Sergio-PL Member

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    Hello everybody.

    At first I'd like to say hello as it is my first post on this forum.
    I'm not yet a hybrid owner but working on it.

    Here in Poland we have 3 Prius based hybrids available on the market.
    1. Prius gen 3
    2. Auris HSD
    3. Lexus CT200h

    All of them are rated 136 HP, similar fuel economy (about 4.0 l/100km).
    Then similar are power modes:
    1. Eco
    2. Normal
    3. PWR (called sport in Lexus)

    While reading back and forth catalogs for those cars I've found that in Lexus Eco and Normal modes MG2 is rated 500V max and in Sport mode (besides remapped throttle and lower/more direct EPS) MG2 is rated at 650V.

    I wonder if the same differences in voltage applies to both Prius and Auris HSD. At closer look all three seem to be the same car repackaged in different body with different accessories added. (And Auris produced in UK rather than Japan - but it doesn't count in engine power)?

    Best regards,
    Sergio
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    bisco cookie crumbler

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    qbee42 My other car is a boat

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    No for the Prius. All three modes in the Prius use the same voltage and produce the same power. You can accelerate just as fast in ECO as you can in PWR.

    Tom
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    Sergio-PL Member

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    Thanks Tom.
    Anyway it is quite interesting why CT200h has a lower voltage than Prius. Energy conservation to meet or exceed Prius MPG ratings in real life?
    I'll keep digging while waiting next few months for Prius.

    S.
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    kbeck Active Member

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    Sergio,

    Don't pay too much attention to the voltage. What batteries and such supply to the motors is Power, which is related to voltage by P = VxI. Second, the amount of energy stored in the batteries determines how far you'll go. Batteries are rated in Watt-Hours (That's units of Power x Time). For example, if you've got a 100 W-Hr battery you can (supposedly) get 100 Watts out of for One hour, or 10 Watts for Ten Hours, etc, after which the battery will be discharged.

    So, in principle, if you have a 100 V battery and a 300 V battery, both of which are rated for 1 kW-Hr, both of them will take you the same distance, assuming that they're each matched to the proper voltage motor, switching electronics, and so forth.

    It's the secondary effects that give engineers ulcers, though. Higher voltage batteries deliver less current (P=VxI, remember) for a given power level; less current can be a good thing, since the losses in the wires in the car are related to the square of the current magnitude (Presistor = I * I *R, where R is the resistance in the wires, I is the current, and Presistor is the power loss in the wires). This is the direct reason for electrical high tension wires: The higher voltage means less I2R losses in the overhead wires and so forth.

    However, higher voltage doesn't always make sense. In the Prius (and other similar hybrids) higher voltage means thicker insulation, higher voltage switching transistors, more losses in high voltage capacitors, and so forth. Further, what particular high voltage one gets to is dependent upon battery chemistry, and, of course, there's always secondary effects on how much battery energy storage, lifetimes, and so on that are also functions of current and voltage.

    The short answer: It's complex. Higher voltages are more the norm these days, but a higher voltage doesn't directly get you bigger range or anything. If you do compare anything, compare the battery energies, not the voltages. And, finally, with a hybrid, it's not directly how big the battery is, it's the overall gas mileage that really counts. (Until the battery gets so big that the car basically drives around on electric only, a la Volt. And the Volt has Issues with gas mileage when you drive from Boston to Chicago, unlike the Prius.)

    KBeck
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    Sergio-PL Member

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    Good job and good explanations of electricity basics.
    But I'm aware of the whole electronics story and that's why I asked the question.
    I took 3 similiar cars with the same hybrid engine, same battery and probably same interconnecting cable diameters.
    Given the same current limit (same cables, engine, inverter) and lower voltage total power delivered to the engine will be lower at 500V than at 650V, meaning less traction battery power consumption.

    That's why I think it is interesting that (theorethically) most power efficient Prius works at 650V max voltage on all power modes and CT200h is limited to 500V in Eco and Normal modes (I assume gas pedal to the floor).

    I've tried to find for some time comparison between acceleration in Normal and Sport modes but didn't found any yet.

    I can think of two main reasons for that:
    1. Increase FE while having bigger Cd = 0.28 value
    2. Increase difference between Normal and Sport mode (sharper accelerator curve, higher max voltage, less instrusive VSC and less EPS).

    I like Toyotas, now I'm driving third one and already know that Toyota does anything only in their cars if has some several reason for that. And most of time are economical or durability reasons.

    And... whatever we figure out here it seems that EU spec Prius has a bit different (HUD, sharper accelerator curves, longer ECO lamp range) from US spec so I will have to figure out how everything I'm reading here for few weeks now applies to EU model as soon as I can get my hands on it ;)
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    sipnfuel New Member

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    This isn't strictly correct.

    The voltage that MG2 runs at is independent of the battery power consumption.

    The Prius has an inverter between the battery and MG2 that supplies MG2 the proper voltage, current, frequency and phase.

    The battery is DC thus we can use the simpler P = IV calculation. While MG2 is a three-phase AC motor and we have to use the equations for AC. Current and Voltage aren't necessarily in phase. Also, when we say the Prius runs at 650 Volts, that is the nameplate RMS Voltage.

    Just FYI, MG2 can run at high voltage and low power, or at low voltage and high power (and low/low, high/high). Just depends on the current and the demand from the driver.

    Personally I think the 500V vs 650V stuff was something the marketing department made up, or someone who didn't understand the principles butchered the engineering specs. Although it is possible Toyota runs a 650V motor at 500V (it would simply require a software/programming change), all three HSD variants can run at 650V if it needs to.
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    David Beale Senior Member

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    Well, actually the inverter doesn't change the voltage. It -may- change the time on/off of the square waveform it feeds the MGs, but I doubt there is any difference. What you are reading is marketing hype!
    What the "mode" switch actually does is change the rate at which power -demand- (the drivers input) is acted upon. In other words, it changes how much throttle you need to get X amount of power. "Power" mode just increases the output faster, with less throttle required. The maximum power is the same in all modes. The minimum power is the same in all modes.
    There are a few other things the "mode" button does too. It may increase or decrease the A/C cooling to get better mileage or better cooling, for example.

    None of it directly controls the voltage to the MGs.
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    sipnfuel New Member

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    This is true in the strictest sense. The "actual" inverter in the Prius only generates the square wave form and does not change the voltage.

    When I say "inverter", that is short hand for "Prius Inverter Assembly" which includes the DC-DC Converter, Inverter, IGBTs and Filters, which for all intents and purposes does output a variable voltage.

    While it has some second order distortions in the wave, it is for this application practically a pure sine wave.

    It's commonly called "the inverter" even though that's only one of components.

    This is how I understand this ambiguity to be.

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