battery removal thought experiment

Discussion in 'Clarity' started by nerd king, Aug 2, 2020.

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  1. rodeknyt

    rodeknyt Active Member

    I would guess that we had maybe 50 or so miles of EV on the entire trip. The car was in HV mode except for getting from wherever we were staying for the night to the Interstate (or from the Interstate at the next destination) and to/from eateries. We weren't doing any sightseeing between stops except for Durango where we walked to the train to Silverton; Denver where we began and ended a Tauck bus tour around the state; a little in Bend and Corvallis, some of which was in friends' or familys' cars.

    As far as how many times we were able to plug in, that was five. So, you can deduct the 50-odd miles and that would probably make a 1-2/10ths reduction in the MPG, which was 43.6. I wouldn't know how to calculate any miles we got from plugging in when using HV mode.
     
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  3. MrFixit

    MrFixit Well-Known Member

    If you "plugged in" five times, and let's say each plug-in charged from 25% to 100%...
    That would mean that you got an additional ~175 miles due to the added electricity.

    Roughly speaking, then your gas mileage would actually be closer to 42. This is still very good in my book.

    I am not trying to split hairs, but significant charging along the way could artificially inflate the apparent HV gas mileage. In your case it didn't (because your electric use was a very small portion of your overall miles). If someone were to run the battery down and plug in every day on a road trip, it could become a much bigger factor.
     
  4. David Towle

    David Towle Well-Known Member

    36 seems awful. I don't even look at the computer, just divide miles by gallons at each refill. And I almost always refill the battery to full via HV Charge before each gas fill.
     
  5. I agree, 36mpg is disappointing.

    Two questions:

    1) Are you using most or all of your EV range in addition to your HV range between fill ups?

    I’ve been operating in HV only in order to obtain these dismal mpg figures.

    2) How are you able to refill your batteries to “full” using HV Charge?
     
  6. David Towle

    David Towle Well-Known Member

    1) No I end with the same charge I started. I run on the highway in HV, but around town (when its warm) I alternate days between using EV 1 day then HV Charge to refill the batteries the next day.
    2) That was a misstatement, sorry, I fill them as full as they can get about 60% just before a gas fill.
     
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  8. rodeknyt

    rodeknyt Active Member

    By your reasoning, there really is no way to determine actual MPG when using HV mode. Since some battery gets used even during HV, not all of the miles are strictly from the ICE. But, that is how hybrids work (all of them). That would mean that the MPG ratings for any hybrid are inflated because there's always some battery being used for propulsion. Other than the actual miles that are known to be in EV, how do you come up with your conclusion that plugging in gave me miles that have to be subtracted?
     
  9. MrFixit

    MrFixit Well-Known Member

    When you operate in HV (or, as you say, any Hybrid vehicle), all of your miles come from gasoline. Yes, the vehicle alternates between using the battery for propulsion and gas, but keep in mind that while in electric mode, that electric energy (in the battery) came from the gas engine too. Therefore your mileage is fair, and entirely from the gasoline (because there is no other input).

    With the Clarity (and other PHEV's), there is an external electric input. All of the electric energy that you input (during the test) via that plug did NOT come from gasoline, and therefore it distorts the apparent MPG. Also, you really have to consider the SOC both before and after the test. Maybe you start with 100% SOC, drive around for a while (maybe some in EV and some in HV). In the end, if your EV miles are zero, then some of your miles (a full charge's worth) came from the power grid and you need to subtract them when calculating your MPG.
     
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  10. Would there be a difference in HV mpg between 2 vehicles making the same trip entirely in HV, one with fully charged batteries (20 bars) and one with fully depleted batteries (2 bars)?

    I’ve driven on the freeway for hundreds of miles with 2 bars. The gauge has never gone lower and EV range shows 0. With a full charge the gauge has always dropped 1-2 bars after several hundred miles and EV range will drop a few miles. This may be part of the design, to allow fully charged batteries to discharge a bit to accommodate regenerative energy.

    On a 700 mile trip in HV, I’ve seen the EV range estimate decline from 60 miles to 48 miles, maybe 3-4kWh’s, and the gauge drop 3 bars. If that rate of discharge continued, it would take 2500-3000 miles to fully deplete the battery. This would indicate that the fully charged battery may have contributed 50-60 miles, or 2% of the total miles driven.

    That would distort the mpg by less than 1mpg.
     
  11. MrFixit

    MrFixit Well-Known Member

    No, I don't think so... In both cases, there was no net charging or discharging of the battery.

    So I would argue that if you dropped 2 bars during a 300 mile trip, then 2 bar's worth of miles came from your electric grid and should be discounted (well, roughly, each bar is worth ~2.5 miles). Subtracting 5 miles from your 300 mile trip when calculating MPG is pretty trivial.

    Agreed... Another trivial example.

    But, suppose you are on a long road trip. Every day you drive 300 miles, and you just let the car do it's thing. The first ~50 will be EV, then the other 250 will be HV. Every night you use a free charging station... Do this for 10 days... You add up all the gas that you used, and all the miles that you drove and calculate a MPG. Your number will seem too good to be true. If the real mileage in HV is 40, this test will deceive you into thinking you really got 48. In reality, 50 out of every 300 miles were "free" and used no gas.

    If you just look at the eMPG that gets reported by the car, it is very deceptive because it always ignores the external power added and artificially inflates the reported number.
     
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  13. I disagree. My experience is that a fully charged battery does discharge a certain amount on a long trip in HV. A fully discharged battery does not appear to either charge or discharge based on the gauge or EV range estimate.

    The example given was intended to demonstrate the behavior of the vehicle that I have observed while operating exclusively in HV and purposely excluded the use of EV range.
     
  14. MrFixit

    MrFixit Well-Known Member

    You didn't state it in your initial example, but I was assuming that HV held at the initial set-point in both cases. If you have a discharge in one case and not the other, then I agree with you that there would be a difference in HV mileage (albeit a small one).
     
  15. MrFixit

    MrFixit Well-Known Member

    It seems to me that the best way to unambiguously know the real HV mileage is to run the EV miles down to zero. Then, even though you haven't commanded HV, the vehicle has reverted to true HV operation. Then measure miles and gas consumed under these conditions. There is no external power being added, and there is no uncertainty due to any changes in SOC (other than the small changes managed by the vehicle's HV mode, and not even visible to the driver).
     
  16. insightman

    insightman Well-Known Member Subscriber

    It would have been so easy for Honda to give us the data we want. The gen-1 Insight had a lifetime MPG readout, but somebody at Honda decided that was TMI. I wish Honda would satisfy my plea for an optional, even if expensive, app for the Clarity that displays all the data a nerd could want. Not just performance and fuel-consumption data, but the information it tracks to switch modes in HV and even the Battery Capacity.
     
  17. I did state that a fully charged battery will show a drop in SOC/EV range after driving for a period of time in HV.

    Theoretically, HV maintains a specific SOC once set. In practice it allows some discharge from a full SOC. I have observed an initial drop of 1-2 bars within the first 100-200 miles. After that drop it has held quite steady, even after an additional 500-600 miles.

    Some data has indicated that the battery will discharge ~4% before recharging begins in HV. My observations support that, in that EV range will fluctuate depending on power demand. Some owners have reported a steady decline in SOC when operating in HV for extended periods.

    I believe there are two main reasons that explain the gradual reduction of SOC while HV is engaged.
    1) There is a 99% chance that the vehicle will be turned off with the SOC below the set point. The SOC is constantly fluctuating between the set point and 4% below the set point. Unless the ICE is allowed to run until the set point is reached, some discharge will occur at every stop.
    2) The default operating mode is EV. If HV is not engaged immediately upon starting, additional discharge will occur.

    Ultimately, in our PHEV, we can easily determine HV range by operating exclusively in HV. SOC may taint the results by up to 2%, which I would consider within the margin of error. We can also easily determine actual miles travelled in EV, provided the ICE does not engage due to excessive power demand or a system check.

    One thing we can’t easily determine is mpg with the ICE, because we cannot operate exclusively using the ICE.
     
    insightman likes this.
  18. MrFixit

    MrFixit Well-Known Member

    Well, it's semantics to some degree, but by my definition, HV mode is exclusively the ICE. If you get past the nuances of imperfectly 'holding' the SOC for a variety of reasons, then the MPG is exclusively the ICE (just like all the other hybrid vehicles in the world), and that is what matters to me... Gas in, miles out.
     
  19. insightman

    insightman Well-Known Member Subscriber

    HV in my definition means "Hybrid Vehicle," although Honda never explicitly defines those two initials AFAIK. HV combines and alternates EV and ICE propulsion in mysterious and magical ways.
     
  20. Pooky

    Pooky Active Member

    I think what @MrFixit means is that to determine HV efficiency, you need to test HV mode in the same way you would test any other hybrid vehicle: without plugging in. I believe he means, and he may correct me if I misinterpret, that the ICE should be exclusively providing power to both the wheels and the battery (apart from regenerative braking, but macroscopically that is also a conversion of the ICE's energy); no outside electricity sources like plugging in. In that sense, the ICE is doing 100% of the work in the same way a normal hybrid would.
     
  21. insightman

    insightman Well-Known Member Subscriber

    Thanks, I did misunderstand @MrFixit's definition. It makes sense that you can't measure true MPG if you also add in E.
     
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  22. The difference being that the ICE does not run continuously when in HV mode, unlike most conventional ICE vehicles. Some cars do shut off the engine when they come to a stop.

    I realize now, that the choice of the words “exclusively in ICE” may have been better understood had I said “with the ICE running continuously”, which is something we cannot force the Clarity to do.
     
  23. MrFixit

    MrFixit Well-Known Member

    Precisely... You have said it better than I.
    In HV mode, it should be a black box (gasoline in, and miles out). Yes, complicated things go on behind the scenes, but to get the real HV mileage, don't add confusion by putting in extra electricity through the plug (or by expending some of the net 17 kWh that was already in the battery during the test)... That is cheating !
     

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