Best (reasonable) highway speed for fuel economy.

[neal adkins]

The EV range gain on the descent, as stated, was actually tremendous. From mid-40’s to 80. I’ve reported on this trip previously in another thread. It was the tail end of a single day, 700 mile trip with 3 fuel stops. The starting EV estimate at the beginning of the trip was 62 miles and the battery gauge had dropped 4 bars upon reaching the final summit.

I suspect that the BMS limits regenerative charging to something close to a 1C rate. So, the ~10 minutes of descending may have added ~2kWh’s of charge to the battery. I ballpark 1 bar at 1KWh, or ~3 miles Those are rough numbers. It is possible that the gauge was about to lose a 5th bar at the summit or that it was about to add a 2nd bar at the bottom. Being down 4 bars isn’t nearly full in my book, and we know that the car only dumps excess regen under moderate to heavy braking after coming off a full charge.

Can you clarify what you mean by “my Clarity is too smart to let me reach the top of the 5K ft mountain climb”?

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.

 

[leop]

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

 

[Landshark]

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.

You’ll have to explain to me how such a practice could reduce battery degradation.

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.

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.

 

[neal adkins]

You’ll have to explain to me how such a practice could reduce battery degradation.

I wasn't saying it will reduce battery degradation but that using hv charge hasn't caused noticeable battery degradation in my case. I emphasized this because protecting the battery is also important in my opinion.

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.

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.

 

[neal adkins]

You’ll have to explain to me how such a practice could reduce battery degradation.

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.

 

[Tek_Freek]

I normally drive at 78 mph with ICE directly powering the wheels (Engine Drive Mode - EDM).

I get about 40 mpg in HV mode. I assume it is that low because of my 'high' speed, but I am willing to pay for gas to avoid drive time. Most of my driving is up and down hills in upstate New York.

How is EDM acquired?

 

[insightman]

How is EDM acquired?

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.

 

[Landshark]

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.

I just don’t see how using HV Charge or not, on uphills or flats, would have any impact on battery degradation.

 

[PHEVDave]

An Outback is a completely different vehicle. It’s AWD and has a 2.5l or 3.0l engine that runs all the time. I had a WRX for a few years and the wife drove a Crosstrek for 5 years.

For the most part, cars, in my experience, tend to get close to the stated mileage when driven in a reasonable fashion. I’m a bit disappointed that the Clarity only gets ~36mpg when cruise is set to 80mph and there are some portions that are driven slower due to traffic. My 2005 Jetta diesel managed 36mpg at 80mph and only increased to 38-40mpg at speeds of 60-65mph. Even our 5500lb 4x4 Grand Cherokee diesel gets 27mpg at 80mph and 30mpg at 65mph.

Granted, the Clarity gets better than stated mileage at 60-65, but is takes a more significant hit than any other vehicle I’ve driven when traveling at 80mph.

Haha! Guess you should reconsider whether driving 80 mph is considered to be driving in a ‘reasonable fashion’!

 

[neal adkins]

I just don’t see how using HV Charge or not, on uphills or flats, would have any impact on battery degradation.

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.

 

[PHEVDave]

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

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

 

[PHEVDave]

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.

I would assume level 2 charging generates more instantaneous heat but do you think it generates more heat in total?

 

[Landshark]

Haha! Guess you should reconsider whether driving 80 mph is considered to be driving in a ‘reasonable fashion’!

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.

 

[Landshark]

then use hv charge during the climb. I have been doing this for about 2 years now and have little to no battery degradation

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.

I just don’t see how using HV Charge or not, on uphills or flats, would have any impact on battery degradation

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.

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.

 

[Landshark]

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.

Imagine if they used the weight of the loaded trucks to pull the empty trucks uphill via a cable system.

 

[PHEVDave]

Imagine if they used the weight of the loaded trucks to pull the empty trucks uphill via a cable system.

Good example.

 

[Mass Clarity owner]

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.

 

[Landshark]

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.

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.

 

[PHEVDave]

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.

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

 

[neal adkins]

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.

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.