Whether or not to use HV mode on Daily Commute

Discussion in 'Honda' started by Lowell_Greenberg, Apr 7, 2019.

  1. I have a 44 mile round-trip work commute with extended hilly uphill/down hill sections. On a fully charged battery, I can complete the commute with roughly 10 miles of EV range remaining at the end, using normal mode throughout. The commute is 50% city (where some of the hills occur, usually traffic free) and highway (flat).

    I think my current approach maximizes fuel economy and efficiency, but I am wondering if ending up with 20-25% remaining charge each day is good for the battery longer term.

    I am tempted to engage HV mode, not on the highway (which I would for longer highway trips) but before going up hills and using normal mode when not going up hills. Despite excellent regenerative braking- the car tends to lose more EV miles uphill then it gains going downhill.

    However, for some reason I am reluctant to do this. I could of course use HV mode on the highway- which would conserve charge- but also decrease overall mileage. Of course the same is true using HV mode for up hill.

    What are your thoughts on this? Also, if there is remaining EV charge, is normal mode generally running battery only- except perhaps when AC or heat is running? I am guessing if it is very hot or cold-I will be forced into HV mode during this commute.

    Sent from my SM-G975U using Tapatalk
  2. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    See the forum discussion thread below, which is chock full of actual hard data and much useful advice:

    "Charge Strategy for Max Battery Life"
  3. Thank you. Quoting from one of the responses in that thread:

    "What was enlightening for me was that the charge/discharge cycle itself is actually very benign and doesn't on its own lead to degradation. Cycle count, depth of discharge, and mechanical stress from changes in cell volume are not the root cause of the problem.

    The degradation comes from being at high state of charge, especially in high temperatures."

    So don't routinely floor your vehicle when going up hill (heat), while living in a Palm Spring's summer (heat) or over charge (if the car even allows you to).

    I guess I"m OK :)

    Sent from my SM-G975U using Tapatalk
  4. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    Yeah. I've noticed a pattern of new Clarity PHEV owners posting questions to the forum about the best strategy for maintaining battery life, and I've responded with a description of how to maximize that by minimizing the depth of daily cycling. But stepping back and looking at the larger picture, I think that's a mistake. PHEVs are designed for daily cycling of much of the usable capacity (which is always less than the full capacity of the battery pack), and limit the level of discharge by engaging the ICEngine to keep the battery pack's charge from falling too low.

    Therefore, it's probably a mistake not to use the full EV range available, even if that means running the battery down daily to the point that the ICEngine range extender kicks in.

    After all, most people who buy a PHEV, whether it's a Clarity PHEV or a Volt (sadly now out of production) or even a much shorter EV range Prius Prime... I think those people choose a PHEV because they want to reduce the amount of gasoline they burn by as much as possible. And if that's why you chose to buy the car, then you should focus on how much gas you can save every day, and not worry about how fast the battery is gonna degrade. Likely it won't degrade that fast, and in the meantime you'll probably be saving money -- and almost certainly reducing your carbon footprint -- by using electricity instead of gasoline.

    Now, with a BEV it's different. If you're running a BEV's battery down to the point that it's almost out of "juice" every day, then you're overtaxing the battery pack. Either you bought a BEV with a range too short for your daily needs, or else you're not charging it up sufficiently when you do charge it.

    But PHEVs are not BEVs, and the charging strategy should be different.

    Lowell_Greenberg likes this.
  5. PHEV Newbie

    PHEV Newbie Well-Known Member

    If I was in your shoes, I'd charge to 80% and run that down to about 30% at the end of the day and run the engine once in between to make up the difference (on the freeway, where it's most efficient). That way, your gasoline will stay fresh and your engine will stay in good running condition without piling on the miles. People seem to forget that one of the worst things you can do to an ICE is to have it sit idle for long periods and run it only occasionally. Besides, the HV mileage is so excellent that you should feel no guilt for using gasoline. The battery is small so if you intend to keep your car for 10 years or more, you'd be pretty upset if you lose 50% of the range well before that.
  6. TeeVee

    TeeVee New Member

    I have a similar commute and likely will be short of charge in the winter. Wondering about when to engage HV mode too. I wouldn't mind engaging it for a longer period, but it is very noisy, especially HV charge mode. The engine cycles on for only brief periods, like 20 to 30 seconds when I accelerate and revs like crazy as speed is increased. Then it turns off as I maintain speed. Is this how other hybrids work too (cycling on-off several times a minute)? I was surprised that the acceleration has such an effect on the ICE when there is plenty of battery (> 50%). I thought that the battery would be used for acceleration like in EV mode and the ICE will run for a longer period at lower RPM to keep the battery charged. The cycling of the ICE was surprising since others on here have complained about the ICE staying on for 10+ minutes to warm up. The ICE will only stay on for 30 seconds after I turn on HV mode then it cycles multiple times a minute and revs as I accelerate in moderate local traffic.

    Why doesn't HV mode behave like that? The engine is off for extended periods, so it seems like the same amount of energy could be generated by running the ICE longer at lower RPM instead of cycling it on and reving it to power the acceleration. Maybe this is to avoid charging loss by generating electricity directly to the motor.
  7. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    Running the motor at lower RPM would almost certainly be less energy efficient. The Honda PHEV is engineered to always run the powertrain at the highest energy efficiency possible, and that means running the ICEngine at its "sweet spot" RPM speed. I know the Chevy Volt was engineered to run the ICEngine unthrottled -- that is, with the throttle wide open -- because that's the most efficient way to run an ICEngine. It wouldn't surprise me at all if the same is true of the ICEngine in the Clarity PHEV.

    I can't speak from personal experience, but a lot of Clarity PHEV drivers posting to this forum report the "angry bees" sound of the ICEngine running at high speed is disconcerting, or perhaps even disturbing. But I submit that's just an emotional reaction from those used to driving gasmobiles. It doesn't necessarily mean Honda did a poor job of engineering. Maybe Clarity PHEV drivers just need to get used to it. However, if the sound really is that loud, then perhaps Honda should have used more sound deadening.

  8. TeeVee

    TeeVee New Member

    If that is the case then how come the engine sound changes as the car is accelerated in both HV and HV charge? When I go from 0 to 35, the ICE will kick in around 10MPH and the engine sound increases as I reach 35 and decreases if I release the gas before hitting 35. Seems like if some RPM like 4000 RPM is optimal then it should jump to that right away. And HV charge should stick to that RPM too to be optimal. Instead what I get in HV charge mode is a higher idle RPM and much louder sound as I accelerate. Maybe the idle RPM is the optimal RPM and the increased sound is to provide extra juice instead of draining the battery during the acceleration. The idle RPM in HV charge is not bad. Would be nice if there was a tach display to quantify the RPM. Does OBD-II provide this on the Clarity?

    Yes, the engineers must have figured out what is best from an efficiency standpoint. And maybe that is to avoid pulling charge from the battery since there is loss when charging it.
  9. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    A higher load will cause the sound of an electric motor to change, even if the RPMs don't.

    But I'll note that altho the Volt runs its ICE unthrottled and theoretically at the highest energy efficiency RPM, if you look at the video showing animation of the various driving modes, it shows the RPM increasing a bit when the ICE has heavy demand placed on it. That is, when called upon to simultaneously charge the battery and provide power to the EV motors, it increases its RPM speed a bit under that load.

    Perhaps the Clarity PHEV works the same way. And perhaps the description "most efficient RPM speed" should be thought of as a narrow range of speeds, rather than a single exact speed.

    Hopefully it's clear that I'm making an educated guess here, rather than stating facts. It would be great if we could have a Honda engineer address these questions!

    Last edited: Apr 10, 2019
  10. TeeVee

    TeeVee New Member

    Do you mean the ICE here? The electric motor is quiet as a feather (at least in EV mode). My comment is about the ICE (apparently, since EV mode is so quiete) getting lounder, meaning likely the RPM is increasing significantly during acceleration.
  11. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    Oh, crud. :rolleyes: Yeah, I meant the sound (engine note) of the ICEngine, not the electric motor. Duh!

    Apologies for creating confusion.

  12. I travel 65 miles each way and have found that using the HV mode on flat sections of the freeway and the electric motor up the hills is the most efficient by far. On downhill sections I never use HV mode, it seemed to regenerate at a slower rate for some reason. Heading to work I get about 140 mpg and heading home uphill I get about 80 mpg. I charge on both ends of my commute. Everyone’s commute is different, try different combinations and see what works best for you.
    Lowell_Greenberg likes this.
  13. KentuckyKen

    KentuckyKen Well-Known Member

    If you're ending your drives with 20 to 25 % SOC, then don’t change a thing. That is being very kind to your battery in regards to depth of discharge.

    You can play the don’t charge it up all the way game but I think the BMS keeps a buffer at the top as well as the bottom so IMHO it may gain you much. However to know for sure we’ll have to wait 8 or 10 years and compare notes. I predict it will be a very small difference in capacity/longevity.

    Also if you don’t charge up to 100 % usable SOC, it’s conjectured that you will prevent the BMS from balancing the cells. So if you don’t charge up to 100% usable SOC, it is suggested to occasionally do so to get the benefit of cell balancing.
    Just my 2 cents and you get what you pay fo.
    Lowell_Greenberg likes this.
  14. KentuckyKen

    KentuckyKen Well-Known Member

    My last post #13was supposed to say IMHO not gain you much

    My apologies for poor texting skills
    Lowell_Greenberg likes this.

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