Charge Mode -> EV: Not Zero-Sum

Discussion in 'Prime Fuel Economy & EV Range' started by mr88cet, Dec 26, 2017.

  1. mr88cet

    mr88cet Senior Member

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    This is the third time we’ve had a chance for a road trip (meaning substantially beyond the ~30-mile EV range).

    I wanted to charge up full, then mostly use HV, keeping the EV range in reserve. However, after a fill-up stop, I forgot to switch in HV, so it burned down the battery anyway. Therefore, I kicked in Charge Mode and charged the battery up to close to its original charge level.

    That seemed like a good opportunity to answer an interesting question: Do you get the same overall MPG driving 200 miles in HV, as you get if you drive 10 miles on EV, then use Charge Mode to add 10 EV miles, then drive the rest of the same 200 miles in ordinary HV Mode?

    That is, do the 10 EV miles (MPG = quasi-infinity) cancel out the loss of the lower MPG of operating in Charge Mode?

    The answer appears to be “no”: I saw about 52MPG overall on that 200-mile trip, and the overall MPG was still recovering when we got to our destination. That, as opposed to on another equivalent, pure-HV trip, where we got 56.8MPG. Also, that 56.8MPG was with climate control (AC) on (today it was off).

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    #1 mr88cet, Dec 26, 2017
    Last edited: Dec 26, 2017
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  2. bisco

    bisco cookie crumbler

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    makes sense right?
     
  3. goinskiing

    goinskiing Active Member

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    Ok, this is something that I am probably missing, but what exactly is charge mode?
     
  4. mr88cet

    mr88cet Senior Member

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    Reasonable question!

    In short, from EV mode, press and then hold for a seconds, the EV/HV button. It will not only put you into HV mode, but also make a point to burn a little more gas in order to charge up the EV-mode portion of the battery. Otherwise, HV mode is, essentially, a battery-hold mode (keeps the battery charge level approximately where it was when you went into HV mode).


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  5. Tideland Prius

    Tideland Prius Moderator of the North
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    It uses the gas engine to recharge the HV battery up to 80%. To activate it, you press and hold the EV/HV button. According to @bwilson4web, it's best to use it at around 50-60mph in terms of efficiency.
     
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  6. goinskiing

    goinskiing Active Member

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    I didn't even know this was a thing! There's still more I'm learning about this car and I love it!
     
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  7. 2k1Toaster

    2k1Toaster Brand New Prius Batteries

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    And thanks to physics you will have some energy conversion losses. Going from dino to electric and back to motive is less efficient. This has held true since the beginning of Prius time. Same reason why people even in the Gen-2, 14 years ago, that tried to parade around in EV mode as much as possible found their overall mpg's lower than when they just drove it. Since there was no plug, it all cam from gas one way or the other.
     
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  8. goinskiing

    goinskiing Active Member

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    True. If you understand how the car works and some basic physics you can eke out a few more MPG than just the standard operation, but it does require that you know when to use certain knobs\options. I like knowing all the available options and when to ideally use them for maximum efficiency. For me, this is part of the fun of a Prius. :).
     
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  9. mr88cet

    mr88cet Senior Member

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    I call that “battery surfing”! (Driving in semi-contorted ways trying to prevent the @#$% ICE from cutting in.)

    Anyway, yes, largely true. Speaking in broad generalities, the higher the speed at which the engine kicks in can have a substantial effect upon MPG. The problem on a gen-2, of course, is that MG2 alone has very little torque, and the battery is tiny, so you can rarely get up to any appreciable speed before the engine has to kick in.


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  10. 2k1Toaster

    2k1Toaster Brand New Prius Batteries

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    MG2 is sufficient if you want to force it to drive in EV. Add an EV button and zip around under 35mph pretty briskly for a 1980's vehicle. If you actually do the OOG modification you can drive up to 65mph only on electric, faster downhill :). The 0-40-ish mph range is nice and snappy. The 40mph to 52 less so. The 52 to 65 is anemic. Around town, you'd blend in with all the other drivers. On the highways around here, certain death. Lots of novel ways of adding battery capacity, but all are now out-dated since you can just go buy a Leaf or a Prime. :D
     
  11. goinskiing

    goinskiing Active Member

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    I did my first long road trip with the Prime (still on it actually) and found the best time to use charge mode is when you’re on a steep grade downhill.


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  12. Old Bear

    Old Bear Senior Member

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    As I understand the design purpose of "Charge Mode" is that it can be used to bring the traction battery up to a workable charge level (80%) for driving in places where only zero-emission vehicles are permitted.

    Some European cities have adopted zero-emission rules for bringing a passenger car into the center city on certain days. The "Charge Mode" can be used in circumstances where one's commute extends beyond ordinary EV-only range and where one must be in EV-only mode for a particular portion of the trip.
     
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  13. mr88cet

    mr88cet Senior Member

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    Hmm... I’d think you’d want to use “B” on the shifter for that...
     
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  14. goinskiing

    goinskiing Active Member

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    I did this with a combination of B mode and charge and seemed to work pretty well. Worked to give enough for around town driving since we didn't have charging capabilities at the hotel.
     
  15. Old Bear

    Old Bear Senior Member

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    Charge Mode will bring the traction battery up to 80% and then will switch to EV.

    However, when descending hills, "B" will add charge and can bring the traction battery well above 80%. (At that point, the internal combustion engine will become involved to help slow the vehicle just because the traction battery would be harmed by trying to force more energy into it from the braking process.)

    Remember, when running in HV mode, the vehicle is constantly adding charge to the battery when decelerating and using available charge from the battery when cruising or accelerating. This is one of the beautiful parts of a hybrid vehicle, whether plug-in or not.

    If you have the Prime Advanced, you can leave the energy monitor visible on the bottom of the display screen under the map -- or have it fill the entire screen. It also can be displayed in the "MID" on the dashboard of all Primes.

    Toyota-energy-monitor-screen.jpg Toyota-energy-monitor-MID.jpg

    The energy monitor will help you understand what's going on in various modes and under different driving conditions.

    Just don't become so engaged in watching the display that you forget that you're driving a moving vehicle!!
     
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  16. stevepea

    stevepea Senior Member

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    Hm, perhaps you played a 4-minute low b-flat on the contra during one trip, but not the other? Those sympathetic vibrations can affect the MPG, you know... ;)

    Well I kind of figured that your results would be better with HV over Charge Mode. I can't think of many instances where Charge would be a plus (maybe just to avoid a warmup cycle the next day if you can't charge overnight and only need it for 3 miles, or some strange scenario like that) but generally I think it's better just to go in HV. Most of my drives are over the EV range, and I just let it use normal HV instead of using the charge mode.
     
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  17. breakfast

    breakfast Active Member

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    I very rarely use charge mode, but it can be handy. Beyond the scenario @john1701a mentioned of having some short trips once reaching the destination where one can avoid the warm-up cycle, here's some others:
    1. I only have a couple of miles of EV left, and I just realized I'll be hitting a huge traffic jam in 20 minutes. It might be more efficient to charge using CHG mode vs having the engine occasionally kick on while idled in traffic... and in any event, it's a nicer feeling to sit in a big traffic jam without the engine kicking on
    2. (really 1a) Now that I'm closer to that traffic jam, maybe I'll avoid it by going through a residential area... and now I can use those EV miles I charged up to go through the residential area without any emissions
    3. Wow, it's a hot day - I'm going to an event in the hot sun, and I'm realizing that I'd really like to use the "AC button" on my remote to cool my car for 10 minutes before I leave for home, and there's nowhere to plug in, but I know (from reading the owners' manual!) that I need to have the battery sufficiently charged more for pre-conditioning to work
    4. I know I'll be parking in a friend's driveway, or a parking meter in the city, and shifting the location of the car around a lot once I get there, so let's have enough battery charge to avoid triggering the warm-up cycle
    5. I'm picking up a friend at the airport, and I want to show them what EV mode feels like. I expected to be able to plug in when I arrived at the airport, but all the charger spots were taken (this really happened to me, but I didn't think of using CHG mode at the time)
    6. (Speculative but logical) I know I'll be doing some mild to moderate uphill driving for a while - I should be able to be in CHG mode while keeping the engine in its most efficient "sweet spot" - lessening the mileage penalty of adding those EV miles
     
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  18. goinskiing

    goinskiing Active Member

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    Very well thought out post. In hindsight, I was thinking that downhill was the most efficient place to have CHG mode, but the more I think about it and after reading other peoples' posts, it would seem the penalty would be the least on an uphill stretch where you're already using the ICE. I'm curious to know which would be most efficient.
     
  19. rickd24

    rickd24 Junior Member

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    I'd like to know the answer to this too. We're going to be taking a road trip soon through the Rocky Mountains so there will be lots of uphill and downhill driving and I'd like to know the best strategy. Thanks in advance.


    Rick
     
  20. Skylis A

    Skylis A Senior Member

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    Is this one of those times where using a ScanGauge to monitor the RPM is helpful so that one can use Charge Mode at the efficiency point of the engine (around 2000-ish)?
     
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