Charge Mode/Highway Question

Discussion in 'Prime Fuel Economy & EV Range' started by #TeamPrius, Jul 19, 2019.

  1. #TeamPrius

    #TeamPrius New Member

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    Hi there,

    It seems as though, when in charge mode and on the highway, the main observable difference is that the engine does not shut off and go into EV mode periodically. It also seems as though this behavior mimics what the generation 3 Prius was like - the engine was always running and perhaps charging the battery at speeds of 45 MPH and above, if I recall correctly. I’m therefore wondering if it makes sense just to leave the Prime in charge mode on the highway, assuming the stored charge will be used later. Given that the warm up cycle for the ICE is its most lossy time of operation, could it make since to use charge mode if it means I won’t use the ICE at all on a return trip, therefore consolidating ICE driving around a single warm up cycle?
     
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  2. schja01

    schja01 One of just a few in Chicagoland

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    Use Charge mode in anticipation of using EV mode and you do not have the option of wall charging else just use HV mode on trips.
     
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  3. bisco

    bisco cookie crumbler

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    welcome #TeamPrius! any relation to PriusTeam?

    charge mode is costing you something. there are threads here with a lot of testing
     
  4. jb in NE

    jb in NE Senior Member

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    Yes. Assuming it is less expensive per mile to charge from the wall than run on the ICE, it is best to arrive home with as empty a battery as possible. If the ICE is running anyway and charging the battery from it will get you home on EV, that may be a good option.

    If you have a routine trip that traces the same route, some experimentation may be in order. If I have to run the ICE (for example, to get to/from my daughter's house, which is a 40+ mile round trip including expressways), I have learned where and how long to run the ICE on the highway (not in charge mode) so I get home with a nearly empty battery.
     
  5. #TeamPrius

    #TeamPrius New Member

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    Thanks for the replies so far. Let me refine my question. I always hear that ‘charge mode costs you something’. However, it seems to me the car is always sort of in charge mode to a degree. Whenever there is excess power and the ICE is on, the battery is charging. During highway driving in HV mode, the ICE will go off and the car will run in EV mode when the load is low. If the state of charge gets too low, the car will not enter EV mode and the ICE will remain on at lower loads while the battery is re-charging. Then, the cycle repeats. (This is how remaining EV miles are preserved if running in HV mode; the car seems to use 5-10% of the battery, charging when the bottom of the range is reached.) So, would it be more efficient to just leave the car in charge mode during a highway trip if it meant the return trip could be entirely in EV mode, thus eliminating an engine warm up cycle?
     
  6. bisco

    bisco cookie crumbler

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    you're over reaching. the car goes into charge mode when it is more efficient to do so, not all the time.
    one thing might make it worthwhile, if you're m/kwh cost more than your mpg.
     
  7. Salamander_King

    Salamander_King Senior Member

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    I don't think so. you can only charge up to 80% of EV SOC. If you are on a highway on your way back and can make it all the way with EV, that means one-way distance is only ~20 miles. I doubt you can charge all 80% in that short distance. If the distance is that short, it would be much more efficient to charge your car at home before starting and use full charge on your way all in EV and come back all HV, assuming that you don't need EV drive within a city at your destination. If your destination is further than 20 miles, and your drive will include some in-city slow traffic either end of your trip, using and saving EV range for those in-city drives and use HV on a highway is the most energy-efficient way to drive.
     
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  8. Tideland Prius

    Tideland Prius Moderator of the North
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    I understand what you’re saying but that isn’t technically charge mode. It is simply running the engine at an efficient rpm for the load and any excess is stored in the battery. The computers have figured out that it’s more efficient to run at a higher rpm (closer to the BSFC sweet spot) and store the excess power (even with conversion losses) than it is to run the engine at a lower rpm to fit the exact power output required.

    CHG Mode doesn’t take any of that into account. It simply sends the engine rpm higher with the sole purpose of charging the battery (of course it’ll send power to the wheels as necessary or if you need more power e.g. accelerating).

    In the first case, you’ll almost never see the SOC change (I don’t have Hybrid Assistant or a Scangauge but I’d wager it won’t change more than one percent)
     
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  9. #TeamPrius

    #TeamPrius New Member

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    Thanks. Makes perfect sense.
     
  10. vvillovv

    vvillovv Active Member

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    I agree with you when describing the scenario TeamPri is asking about.
    That is when using the bottom of the pack after the EV part of the pack is used up.
    I haven't run in HV too often but when I do I usually try to switch to HV and leave it on HV with a full plug charge in the pack.
    With my driving style it just seems to work out better for me that way. YMMV
     
  11. Curlyone

    Curlyone Junior Member

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    Yes charge mode has a cost, it lowers you MPG to charge the battery. However I think the cost is recovered when you use the charge. This is assuming you charge when it makes sense, steady highway speeds, and you use the charge when it makes sense, in city driving.

    For an example I just got back from a 4 day weekend trip, total miles 973 miles, with 57.2 MPG. I used EV when getting off the highway to refuel/rest/etc, and also while getting back on the highway to accelerate up to speed. As soon as I was cruising again I used charge mode back up to 80%. On the way up I stayed on secondary highways, speed was 60-65, MPG stayed around 60. On the way home I took a different route, speed was 75 the whole way, and the MPG started dropping slowly.

    There were times when going up steep hills it would stop charging while under load. There were also times when the ICE would shut off while going down big hills, on more mild down hills ICE would sometimes not be driving the wheels, with all the work going to charging. But in all cases it went back to charging after the hills.
     
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