I guess I was bored...

Discussion in 'Clarity' started by Fast Eddie B, Sep 5, 2019.

  1. Fast Eddie B

    Fast Eddie B Well-Known Member

    ...so I collected a couple of data points related to recent threads.

    Karen and I found ourselves on a relatively level portion of I-75 today, so I decided to try a couple things.

    First, I got the instantaneous mileage display up on the driver’s display. I then compared the gas mileage displayed with both HV and HV CHARGE selected. At 75 mph, HV returned 40 mpg, HN CHARGE about 30 mpg. Seems like a huge hit, but then again I was building EV miles that down the road would result in zero gas used, so the calculus of HV CHARGE’S effect on efficiency is indeed complicated.

    Second, I intentionally took the EV miles remaining down to 0.0. I then engaged HV CHARGE mode and noted for the odometer. The EV range stayed at 0.0 for a mile or so. I then switched to the instantaneous mileage for a minute, then back to the EV range, which had jumped up to 3.2 EV miles remaining, in less than 3 miles driven total.

    At least I fended off boredom for a few minutes!
    Hoon likes this.
  2. sniwallof

    sniwallof Active Member

    The 40/30 number is consistent with past reports by @jdonalds, and others.

    It may be possible to determine the generator size from these sorts of tests. If we can guesstimate or measure the instantaneous electrical power in kW used to keep the car moving forward, say on level ground at some speed, and we can also know what power level causes a given observed hv charge rate of some number of EV miles/over a recorded charge time (based on battery charging delta kW-hrs, change in energy stored), then, If I'm not missing something, the sum of those two kW numbers (forward propulsion power + hv charge power) is the generator output power in kW, at least for that driving condition (i.e. some forward speed, with all the associated lesser factors of wind speed, road grade, tire condition, etc.). It's not max generator output (unless going really fast), but at least there could be some more data points for various known conditions.

    It's not the same because of conversion losses, but we can probably kinda guesstimate power levels to charge for EV miles/time from our various L1, L2 charging experiences, probably closer to 32A L2, because hv charge is still faster that that if I remember correctly (and possibly with less loss).

    Both the Volt and Bolt report instantaneous power numerically in kW, Clarity does not. I suppose short of figuring out the power scale (which may be non-linear, or vary with time and conditions; I looked through old threads once, and could not find any consensus on any numeric calibration for the power ring and tick marks) someone can probably guesstimate Clarity instantaneous power based on weight and speed to some rough first approximation.
    Last edited: Sep 5, 2019
    Hoon likes this.
  3. 2002

    2002 Well-Known Member

    At least on the surface the calculation is relatively simple. If HV for a particular drive is 40 mpg, then of course to state the obvious if you burn one gallon of gas you would expect to go 40 miles. Instead you switch to HV charge, thus reducing mpg to 30 so you only go thirty miles on that gallon, which is ten miles short of how far that gallon would have taken you in regular HV. However the big question then becomes did you build up 10 miles of additional EV range, if so then it's break even because you can still reach 40 miles on that one gallon. However if you built up less than 10 miles of EV range, say only 7 miles, then the gallon of gas will only take you at total of 37 miles, so 37 mpg instead of 40 mpg.

    Of course this all depends on the accuracy of the displayed values:
    - Accuracy of displayed instantaneous HV mpg
    - Accuracy of displayed instantaneous HV Charge mpg
    - Accuracy of displayed EV range

    Checking the accuracy of those values is where the difficulty lies. Or else tossing out even trying to use the displayed values and going back to the idea of measuring actual gas used and actual EV miles driven in a tedious and complicated series of test runs.
    Hoon likes this.
  4. Fast Eddie B

    Fast Eddie B Well-Known Member


    Of course! Seems so obvious in retrospect.

    Such a test is kinda hard around here in E TN, where even interstates are rarely exactly level, or even consistently a steady grade over a given distance.

    I’ll still fall back on physics and do my best to avoid HV CHARGE by selecting HV with my desired EV “reserve” until my destination is within range. But it’s good to know the hit on fuel economy is not as draconian as I had assumed. And with local fuel prices between $2.10 and $2.30, any hit to our pocketbook would be trivial in any case.
  5. Hoon

    Hoon Member

    Thanks for the experiments. Is 40 mpg in HV Mode while driving in Gear mode?

    In HV Charge mode, it can’t be 100% efficient so I don’t think 30 miles + 10 EV miles on one gallon is going to happen. The benefit would be for later on when you need extra power from the battery such as going uphills or harder acceleration vs not having any charge at all. I know I’m pointing out the obvious, lol.

    Anyone have an idea of how much the efficiency is on storing power to battery? Or how about regen?
  6. Fast Eddie B

    Fast Eddie B Well-Known Member

    I don’t think Gear Mode was in play.

    Also, when in HV Mode, when the engine is off, instantaneous gas mileage goes to infinity. So I had to catch it when the engine kicked in. And I guess that further complicates things since the “infinity” stretches are not being factored into the equation.
  7. KentuckyKen

    KentuckyKen Well-Known Member

    Based on reports, reading and tech articles, consider using 92 % efficiency for the AC to DC charger. However, I’ve seen the estimates range from 85 to 95 %. The 92 % estimate agrees with the capacity and charging reported on the forum and is in the ballpark for inverter’s and solar equipment.

    FWIW, the 2nd Law of Thermodynamics means that HV Charge can’t possibly be as efficient as HV. The only real question is how much less efficient is it. And of course it is quite possible with low enough gas prices and high enough electricity prices for it to be more economical but it can never be more or even equally efficient. This would make a great MythBusters episode!
    (Wanna buy a perpetual motion machine or free energy gizmo? They sell them all the time on the ol’ internut.)
  8. 2002

    2002 Well-Known Member

    I think MythBusters would only be interested if there was a theory that using HV Charge for too long will make the car explode.
    insightman likes this.
  9. GV Ottawa

    GV Ottawa Member

    For me, the value of HV Charge mode is in ensuring that there is always a decent amount of EV assist to the regular HV mode on the highway such that HV mode runs as efficiently (and quietly) as it can (ie. no angry bees). In addition, I use HV Charge mode to ensure I have a sufficient amount of EV range left to get to my end point destination once I get off the highway and the car is no longer getting 40 mpg. Your gas mileage will usually be much worse with city driving than highway driving so it is great to be able to use pure EV once back in the city.
  10. Fast Eddie B

    Fast Eddie B Well-Known Member

    But can’t you accomplish the same thing without HV CHARGE by just switching to HV so as to retain adequate EV range? In 20,000 miles I can’t think of I time we’ve actually needed HV CHARGE mode.
  11. GV Ottawa

    GV Ottawa Member

    I use HV Charge if I'm travelling between cities with no other opportunity to plug in and charge the battery. I completely agree that if I'm heading home, or to a location where I know I can charge, then I don't use it. But I've had some multi-day trips with no opportunity to plug in and charge the battery and in those cases I've enjoyed having the option to use HV Charge mode to get some in-city EV miles. I'll use pure EV in the city, run it down close to zero, and then charge the next day when I'm back on the highway with HV Charge mode so I can be back to pure EV in the next city.
  12. Although true with an ICE vehicle, I’m not sure it is true with the Clarity as it is always electric except for “gear mode.” It’s just a question of where the electricity is coming from and if the ICE is running in the city any excess electricity can be stored in the battery. (There are conversion losses when storing to the battery, but this is true in HV charge as well or even when getting back to the set point in HV.)

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