MPG in Hybrid Mode

Discussion in 'Prime Technical Discussion' started by CEJ, May 13, 2019.

  1. Salamander_King

    Salamander_King Senior Member

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    Agreed, as long as you don't live in NE or Hawaii.

    Your Mileage May Vary. I should have used "YMMV".
     
  2. Tideland Prius

    Tideland Prius Moderator of the North
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    Mileage may vary
     
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  3. CEJ

    CEJ Member

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    Not sure what you mean about NE, Hawaii.

    Since I think both you and I are actually getting in the 60’s for HV mpg, this is quite above the EPA estimate of 54 and will impact the calculation. Still find it puzzling that EPA is so much lower. Maybe it’s my limited seasonal experience. But didn’t you best EPA pretty much all year round?
     
  4. Salamander_King

    Salamander_King Senior Member

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    I was just referring to New England states and Hawaii being the higher than average electricity rate in the nation. In those states, EV drive does not save as much as in other states.

    Well, much to my surprise, when I calculated lifetime HV milage on my two years of driving PRIME (see my table in MPG in Hybrid Mode | Page 12 | PriusChat) , the average HV only mileage is currently 53.95 mpg which is almost exactly what EPA number is, with is still better than my previous Gen3 lifetime mileage, but not that much. I think winter HV mileage brings down the overall mileage quite bit in my area.
     
  5. CEJ

    CEJ Member

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    OMG, LOL! By NE, I thought you meant Nebraska, which is where I live. And, believe it or not, I have lived (some time ago) 11 total years in the Boston area (in two stints, one as a student), so I am well acquainted with your stomping ground! And have been back many times since. (Terribly sorry to see Durgin-Park go--ate there many times.)

    Your surprising 53.59 mpg result is interesting and fascinating. As you say, it must result from averaging over seasons. Let's keep an eagle eye on this.
     
    #265 CEJ, Jul 5, 2019
    Last edited: Jul 6, 2019
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  6. CEJ

    CEJ Member

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    I am wondering now, if when calculating the cost per mile in EV, it might be more accurate (and easier) to use the mi/kwh reading on Drive Monitor 2, rather than using the value of the GOM reading when you start off with full SOC (where you have possible error in both the mileage and the fill-up charge). The mi/kwh reading is also conveniently cumulative, averaging over everything since it was last reset. For example, my current reading is 5.2 mi/kwh and would give a cost per mile of .0548/5.2=$0.0105/mi, (using my rate before July 1) and .08/5.2=$0.0154/mi, now that we are in the higher summer rate.

    Whaddya think?
     
  7. jerrymildred

    jerrymildred Senior Member

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    That might be as good as anything, but still not very accurate because they would not count the losses involved in the actual charging, which you also pay for. It would be close, though, if you knew exactly what those losses were. People have offered theories, but I've not heard of anything official.

    The Prime really doesn't offer a way to separate out EV cost per mile from HV cost per mile. That's because the EV% is incremented any time the engine is not running whether or not you selected EV mode. The PiP kept them apart, but the Prime mingles them.

    What you could do, is track your energy consumption from the wall during a fairly extensive time of EV only driving and that would get you a figure, but it would only apply for those temperatures and driving conditions. It could fluctuate by 25% or more.

    I just figure my total cost per mile by using the electricity and the gas consumption over a tankful of gas. Which doesn't happen often unless I'm on a vacation trip. :D
     
  8. Salamander_King

    Salamander_King Senior Member

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    Yap, that is what I used to calculate my lifetime cost of EV on a table in MPG in Hybrid Mode | Page 12 | PriusChat. However, you can not use the wall charge rate to calculate the cost. For a full charge of SOC using ~6.5kWh at the wall is not what you are using for full EV range. For my calculatetion, I have made an assumption on the charge efficiency of 84% from the wall 6.5kWh to battery resulting 5.46kWh for EV drive. This, of course, assumes miles/kWh value given in the Drive Monitor 2 is an accurate measurement. As we all know mpg measurement displayed is 5-7% too optimistic, so I have a reason to believe Drive Monitor 2 miles/kWh is too.

    Screenshot 2019-07-07 at 4.19.55 PM.png
     
  9. Salamander_King

    Salamander_King Senior Member

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    The latest update of Hybrid Assistant shows actual battery kWh used during EV run. I have not checked it on mine yet, but @john1701a have shown the full EV range from 100% to 0% SOC on MID uses 5.22kWh. Prime Prime - understanding kWh | PriusChat He claims his L2 EVSE charge the battery from empty to full uses 5.7kWh at a wall. That would make his efficiency 5.22/5.7=91.6%. For me, my L1 EVSE routinely takes 6.5kWh to charge SOC 0% to 100% on MID. If I use the value 5.22kWh to be the amount of battery charge used for full EV range, my efficiency would be 5.22/6.5=80.3%. That's a big difference, I have no good explanation for it other than L2 vs L1 efficiency differences. I have used a value 5.46 kWh for the amount of battery charge used for full EV range for my calculation. This is based on the assumption that the real traction battery SOC used for the full EV range is 18%-80% (or total 62%) of 8.8kWh battery capacity.
     
    #269 Salamander_King, Jul 7, 2019
    Last edited: Jul 7, 2019
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  10. CEJ

    CEJ Member

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    I guess I am confused. Help! As I understand it, the battery allocates 6.6 kwh for EV and this what my wall meter usually reads after a full charge. So if only 5.22 kwh is available for EV, where did the rest go? Is the energy lost internally in the car after the battery is fully charged (for example, in the process of converting the electrical energy into the car's motion) or does the battery never receive the full 6.6kwh in the first place? Pardon if this is a stupid question.
     
  11. Salamander_King

    Salamander_King Senior Member

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    I don't think the battery allocates 6.6 kWh for EV. From reading others posts, the actual SOC monitored by various OBDII gadgets is showing value like 18% to 80%. The top 20% and the bottom 12% of SOC are never touched for the longevity of the battery. The SOC 12%-18% is used for HV operation after EV range is depleted. 18%-80% makes up 62% of the total battery capacity of 8.8kWh, which is 5.46kWh. This is the number I use for 100%-0% EV drive. However, with Hybrid Assistance app and OBDII, it was shown that the full EV range of 100%-0% used 5.22kWh. It is the only a one-time measurement, and I am not sure every PRIME for all conditions use this same amount for full EV range. I have to test it myself one of those days when I plan to drive more than 40 miles in a single trip.

    I think both of your statements are correct. Some energy is lost at every step of conversion from the wall to the charger to the battery to the motor. You never have 100% efficiency. Meaning that the battery never receives the full 6.6kWh from the wall in the first place.
     
    #271 Salamander_King, Jul 7, 2019
    Last edited: Jul 7, 2019
  12. CEJ

    CEJ Member

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    This is fascinating and I am grappling to follow you. First, do I understand that this means that if the HSI screen shows 100% that actually the battery is only 80% charged (that is 0.8x8.8= 7.04kwh) in order to preserve battery life or whatever by not fully charging it? And that when HSI indicates 0%, the battery is 18% charged (.18x8.8), which can then be used for HV but can go no lower than 12%?
     
  13. Salamander_King

    Salamander_King Senior Member

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    That's correct. However, the real SOC % cut off points vary somewhat depending on whom you ask. Nonetheless, total 62% allocated to EV range 100%-0% seems to be in good agreement among the technophiles who have measured it. Here is another version of cut off points.

    This is still 62% total SOC used for EV.
     
  14. CEJ

    CEJ Member

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    John's thing is interesting and basically consistent with you. To summarize, using your numbers, the battery charge can range from 12% to 80% of its 8.8kwh capacity so the battery will never be completely charged or completely uncharged (like earlier Priuses).

    This would mean that the maximum charge that would ever need to be replaced should be 80%-12%=68%, that is, 0.68x8.8=5.98kwh. Yet, when I replace charge (with SOC at 0%), I typically require 6.6 or 6.7 kwh. I would be surprised if 0.6kwh is lost in the transmission process although there is always some small loss in the resistive heating of the wires. What am I missing?
     
  15. kevin.c

    kevin.c Junior Member

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    5.98 / 6.7 = 89% efficiency. This seems like a reasonable number to me.

    The big contributors are probably AC to DC conversion efficiency and heat from the battery’s internal resistance.

    Also, it needs to run fans, computers, and trickle charge the 12V aux battery, for 5+ hours. Those are smaller but probably not negligible.
     
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  16. Salamander_King

    Salamander_King Senior Member

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    Using my number the bottom of EV range SOC 0% is actually 18%, not 12%. The SOC 12%-18% is used for HV operation after EV range is depleted. So, the total you can replenish from the wall is 80%-18%=62%. That is 0.62x8.8=5.46kWh. As I stated above in comment #268 table MPG in Hybrid Mode | Page 14 | PriusChat this makes efficiency at about 84% or 16% loss of kWh from the wall charge.

    Yeah, that's a lot of lost electrons somewhere, but that seems to be what the numbers suggest. I don't have a degree in electrophysics, so I can't explain why.
     
    #276 Salamander_King, Jul 8, 2019
    Last edited: Jul 8, 2019
  17. CEJ

    CEJ Member

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    So what role does your 12% play? If you are in HV after EV range is depleted, won't it then be the absolute bottom? I realize the 18% will be normally maintained pretty well in HV by the generator and regen braking. So usually the replenishment will be 62%.
     
  18. Salamander_King

    Salamander_King Senior Member

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    When Prime's traction battery is depleted of EV range, the car is basically a regular hybrid Prius. Regular hybrid Prius has a battery capacity of ~750Wh. The regular Prius battery is never charged from the wall, but for the longevity purpose same 62% use rule is implemented, so the actually used portion of the regular Prius is 0.465kWh (0.75*0.62). Prime's 12%-18% is 6% of the traction battery's 8.8kWh total or 0.528kWh. That amount is used for HV operation just like the regular Prius. The number is not exact, but close enough. I think you get the idea. The bottom 12%-18% of the traction battery is what PRIME uses for HV operation without any wall charge.
     
  19. CharlesH

    CharlesH CA HOV Decal #5 on former PiP

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    Also, L1 (120V) charging has been reported to be somewhat less efficient than L2 (240V) charging. My L2 charging typically consumes very close to 6kwh from the wall, per my Chargepoint charger, but people doing L1 charging typically report around 6.6kwh from the wall.This may be due in part to running overhead activities mentioned earlier, such as the 12V trickle charger, the computer that control the charging, and fans twice as long. And I am not an expert on this and let others correct me if I am wrong, but I think the AC->DC conversion process itself may be more efficient when it starts from a higher voltage.
     
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  20. drash

    drash Senior Member

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    Toyota has stated before about 20% of any power usage is from the power electronics loss. As @CharlesH and others have stated before these are used anytime the AC-DC inverters are used and the DC-DC converter as well. These are activated whether you are using L1 or L2. The difference is these are activated for 5+ hours on L1 but only ~2 hours on L2. It’s the same difference as if you activated just the fans on the HVAC system versus using AC or heat. You still lose EV mileage just activating the HVAC system. So it’s basically a time constraint on total power going into the system.

    [edited for clarity]

    iPhone ? Pro
     
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