Burning Gas while fully charged

Discussion in 'Clarity' started by peter sun, Nov 14, 2019.

  1. JCA

    JCA Active Member

    Totally fine; I know I'm being contrarian too :) Which part are you saying is not -- that temp "Lo" with AC off brings in outside air without heating it (I'm pretty sure that's the case, but someone with a thermometer to put in the vent stream and colder outside temps than I have now can verify), or that the climate controls are inconvenient? I should have said "I find them inconvenient"; I know some people are fine with them and that most new cars, at least at the higher trims, have similar controls.

    For me, one of 2 things would be all I need -- having the "AC" control as a physical button with lighted indicator, as it is on most other cars I've owned, or having separate "Heat" and "Cool" temperatures that I could leave alone. When it's say 65 in the morning I don't want the car blasting the expensive electric heat to get to 70 (don't even heat our house that much), and if I spin the temp down I don't want it using AC to cool it down; I just want fresh air. I'd probably set Cool to 70 and Heat to 55-60. When I get a chance I'll start a new thread on this, as it's diverging a bit from the OP's issue and I'm looking forward to learning better ways to use/live with it!

    In a car like this where we're a bit obsessed about exact energy consumption (every post that compares GOM numbers) because the EV range is close to our daily use (which is fine, that's why I bought it because it's a pretty close optimization), knowing when and how much energy heat and AC are consuming is useful. For example, we know EV range goes down when it's cold -- how much of that is due to inherent battery usage characteristics at temperature (which we can't control much) and how much due to using increasing amounts of cabin heat the colder it gets (which we have some control over by dressing more warmly, wearing gloves, using seat heater etc more with cabin heat set lower/off, optimizing which part of the trip uses the engine thus generating heat there if going beyond range anyway, etc).
  2. JCA

    JCA Active Member

    I reread and realized that I completely misinterpreted, you just meant you weren't meaning to be contrarian, not that you disagreed with what I wroe :) Sorry about that! In any case, I still think the answer is "LO means no heat", and what I've felt with temps in the high 40s backs that up, but as soon as we get to the 30s I will measure with a thermometer to be sure.
    mjpmpg likes this.
  3. mjpmpg

    mjpmpg New Member

    Yes, you hit the nail on the head the second time around. I suppose it would have been more accurate to say I wasn't trying to be a wise guy with my question since I'm genuinely curious if setting 'Lo' when it's cold out (say sub-freezing) will actually give me just a bit of heat to get through some of my local trips. I suspect that you're correct in thinking that "Lo means no heat" but I haven't really had ripe conditions to test it out myself yet. Also, I completely agree with your suggested changes to make the climate control more convenient!
  4. vvk

    vvk New Member

    I tried to see if anyone has answered this already and could not find anything. The reason you hear the engine when using regen with a fully charged battery is that Honda is channeling the energy of the regen braking into spinning the ICE (without using fuel,) since it cannot put it into the battery. Very smart.
  5. KentuckyKen

    KentuckyKen Well-Known Member

    True, but when it happens to me, the inductively coupled hour meter I have attached to the #3 spark plug increments up and the exhaust manifold gets hot. This leads me to believe that it is in fact running and burning gas during these events (at least in my Clarity).
    I drive 95% in EV and now that my Clarity is approaching 2 years old and 14,000 miles, it seems to be doing this much less. Or maybe I’m being more careful about hard braking and 4 chevron regen immediately after leaving home on a full battery. Who knows?
    Both @insightman and I, along with many others, would give our eye teeth to know exactly how it dissipates the energy.
  6. insightman

    insightman Well-Known Member

    Honda engineers have published one or more papers that explain how the company's non-plug-in i-MMD hybrids shut off the engine and force the starter motor/generator to turn the dead engine to use up the power that cannot go into the fully charged battery. However, as @KentuckyKen notes, the Clarity PHEV's engine starts and runs in this situation. Honda engineers, again I implore you, please explain!
  7. insightman

    insightman Well-Known Member

    The Clarity PHEV is heavier than the non-plug-in Honda i-MMD hybrids that DO spin the deadened engine using the starter motor/generator to use up the power a fully charged battery cannot accept. Perhaps that's the reason the engineers had to come up with a different scheme for producing a braking effect when the battery is fully charged. My theory is that the starter motor/generator uses up more power by trying to slow down the running engine. This diagram I made illustrates my baseless speculation:

  8. Ray B

    Ray B Active Member

    True. I mean assuming that the philosophy is that the battery is full and can't accept a sudden blast of current, it makes sense that the energy must be consumed in another way, and starting up the engine can seemingly do that to a degree - but only for a short time (quite short). Using the engine as a resistive load would make sense if there was no gas used, and you have shown that it certainly does burn gas. Even more vexing, when I have had the ICE spring to life when braking at ~100% SoC the engine then chugs away for another few minutes, all the while the energy flow shows that it is sending charge to a fully charged battery (that was a second ago being defended from overcharging).

    So certainly the story is incomplete. There is a theory that I have backed that the current sent by the regen is opposed by the current sent by the generator via the ICE, which makes sense to me, but it is not clear what happens over the next 2 minutes of the ICE running, and sending current out of the generator - is it topping off the battery that is already close to or at 100%, or is the battery now supplying some opposing current to neutralize the load given by the ICE+generator? Doubtful, but I'm not an electrical engineer.

    I did find another patent (by Ford in 1992) that has an interesting concept of using the unwanted current to run a resistive heater that would trigger the ICE. I don't know enough about the cooling system to know if that is a possibility in the Clarity, but I haven't heard it mentioned yet as a potential explanation.
    KentuckyKen likes this.
  9. su_A_ve

    su_A_ve Active Member

    Another reason for ICE kicking in is extreme cold temps. Last winter one day with temps in low single digits and having left the car outside, when I pressed the start button, ICE kicked in even though there was over 50% charge remaining.
    KentuckyKen likes this.

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