Best (reasonable) highway speed for fuel economy.

Discussion in 'Clarity' started by Timothy, May 13, 2021.

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  1. neal adkins

    neal adkins Active Member

    With your obvios technical skills it was a little misdirected pun. I think its smarter to use a least half of your battery before approaching a long upgrade, then use hv charge during the climb. I have been doing this for about 2 years now and have little to no battery degradation. But my comment is also an inside joke on how my clarity protects itself from me. Like how it will apply the brake if i approach another car too fast, and warn me if im going off the road and such. The car thinks it's pretty smart. My sense of humor is a little warped. On a more serious note, im very happy with my mid 70's mpg considering about 60 percent highway miles.
     
    Last edited: May 16, 2021
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  3. leop

    leop Active Member

    This is just an interesting tangential comment. In Europe there is a mine on the top of a mountain. The empty electric dump trucks can climb the mountain using only the energy stored in the batteries as the loaded dump trucks descend from the mountain top mine. The battery regen also nearly eliminates all brake wear. This looks like perpetual motion (but is not as the gravitational potential energy of the mined material is used) and is very clever on the part of the engineers and bean counters.

    LeoP
     
    neal adkins likes this.
  4. You’ll have to explain to me how such a practice could reduce battery degradation.

    Those sensors can’t differentiate an oncoming car on a curve from a vehicle traveling in the same direction that I may be approaching at a rapid pace. They also can’t tell when I am intentionally positioning the car to favor one side of the lane or the other. I operate the vehicle with those features disabled.
     
  5. neal adkins

    neal adkins Active Member

    I agree that they are quite annoying. But its its there's also a humorous side.... The implications is that the car needs to supervise we humans and is indeed superior.
     
  6. neal adkins

    neal adkins Active Member

    My emphasis was that using hv charge while climbing long grades hasn't caused any noticeable battery degradation. I recently did an ev range test.
     
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  8. How is EDM acquired?
     
  9. insightman

    insightman Well-Known Member Subscriber

    If you have the infotainment screen displaying the energy screen when you're cruising (not accelerating) at a speed greater than 45 mph in HV, you'll see a gear icon appear between the wheels on the display. That indicates you're in Engine Drive Mode (some call it "Gear Mode" due to that gear icon). If you try to accelerate too briskly while in Engine Drive Mode, the Clarity opens the Engine Drive clutch, leaving the traction motor as the car's sole motivation.
     
  10. I just don’t see how using HV Charge or not, on uphills or flats, would have any impact on battery degradation.
     
  11. PHEVDave

    PHEVDave Active Member

    Haha! Guess you should reconsider whether driving 80 mph is considered to be driving in a ‘reasonable fashion’! :)
     
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  13. neal adkins

    neal adkins Active Member

    I never said it did. But it is a concern with some folks and thats why i addressed it in my comment. As you know 6.6kwh at 32 amps in hv charge mode will create more heat than say a level 1 charger with the car stopped. Heat/rapid discharge lends to degradation. That said, its just a concern with some folks. Obviously there's many factors that effect degradation and it is inevitable.
     
  14. PHEVDave

    PHEVDave Active Member

    I’m assuming you meant to say that at the bottom of the hill, the truck has regained 100% of its charge...
     
  15. PHEVDave

    PHEVDave Active Member

    I would assume level 2 charging generates more instantaneous heat but do you think it generates more heat in total?
     
  16. 80mph is on the slow side of reasonable in California. See also, Texas, Nevada, Wyoming, Montana, Utah, Arizona, name your state. Point being, no other car that I’ve owned in 40+ years of driving has suffered a 20% decline in fuel economy when going 80mpg compared to 65mph.
     
  17. You mentioned HV Charge and battery degradation twice. Why? Why emphasize that using HV Charge hasn’t caused battery degradation if you believe there is no correlation?

    I did not know that HV Charge uses the onboard charger to charge at 6.6kW. How have you determined that this is how HV Charge operates?

    Level 2 charging on the Clarity at 6.6kW is a 0.4C charge rate. This is a relatively low charge rate for lithium batteries. I have witnessed HV Charge bringing the batteries from 2 bars to 10 bars, 50%, in approximately 30 minutes. This would indicate a charge rate of 0.8-1.0C. This is a slightly more aggressive charging rate, but still within the recommended levels recommended by many manufacturers. The higher charge rate is likely the reason Honda limits HV Charge to ~60%.

    The number of charge cycles and the charge and discharge rates are two main factors that contribute to battery degradation. There are other factors as well. We aren’t likely to cause harm to our battery by either Level 2 or HV Charge, charging. Rapid discharging is possible by driving 70mph in EV. This could discharge the battery in as little as 30 minutes. That would not be the best practice for battery longevity, but it isn’t outside the capability of lithium batteries. It is also allowed to occur within the parameters of the BMS. So, Honda has given us permission to drive at high speeds until the battery is depleted.

    You mentioned that the car was smart because of its driver annoyance features that keep the car in a lane and prevent it from ramming other vehicles. I maintain that if the car were capable on any sort of intelligence, the BMS would be at the head of the class.
     
  18. Imagine if they used the weight of the loaded trucks to pull the empty trucks uphill via a cable system.
     
  19. PHEVDave

    PHEVDave Active Member

    Good example.
     
  20. Mass Clarity owner

    Mass Clarity owner New Member

    I'll pitch in my data from our trip this weekend. This was our first long trip with the Clarity. We went from MA to PA and back. About 365 miles each way. Started off with full tank and full battery for each leg. Our strategy was to start each leg with EV mode for the back roads, then use HV on the highway. And switch to EV mode if we encounter a slowdown or stop and go during construction/traffic. Adn then end the trip on EV (local roads). The trip had some hills, but not mountain passes. Mostly used the cruise control and kept it at 67-69 mph. Battery SoC was maintained at about half or more during the HV highway driving. By measuring the fuel added at the gas station when we refueled and looking at the miles driven and looking at the battery (bars), I estimate that we used about 7 gallons of fuel + 50% (maybe a tad more?) of a fully charged battery to go 365 miles. That's 52 mpg plus the consumption of half a battery.

    This exceeded my expectations for how the car would perform. And we felt very comfortable with the car's seats (former car was a civic) and ride smoothness. And everyone we visited was impressed with the car (of course, they'd never heard of the thing).

    I think if one had the patience, you could do even better by driving at 63-65 mph. I think the reason that the efficiency is poorer (compared to other cars) at speeds such as 80mph may be due to the Atkinson engine, which does not have the typical gearing/overdrive capabilities of typical ICEs.

    Also, only saw one other Clarity during the entire trip. Which is too bad, as it is ideal for these type of East Coast drives, in my opinion.
     
  21. Thanks. If you subtract 25 miles from the 365 miles to account for the +50% battery usage, you’re at 340/7 = 48.6mpg. That’s close to what my wife recently achieved driving a fully loaded car at 62-64mph. Others have reported similar fuel consumption at ~65mph.

    It is possible that Engine Drive Mode may not be the most efficient mode at 80mph. Perhaps the engine driven generator, providing electricity to the motor and maintaining SOC would be a more efficient option.
     
  22. PHEVDave

    PHEVDave Active Member

    That’s a good point. And it may be why the Clarity’s efficiency drops off more sharply at higher speeds than other vehicles.
     
  23. neal adkins

    neal adkins Active Member

    Hi Landshark. I feel like i have allready answered many of your points of contention in my previous post. I got the info about the 6.6 kwh 32 amp charger from a honda web page. I keep an open mind about causes of battery degradation and don't claim to be an authority. But i am happy that i have no noticable loss of ev range.
     
    Last edited: May 17, 2021

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