1. Attachments are working again! Check out this thread for more details and to report any other bugs.

HV mode usage of EV battery portion

Discussion in 'Prime Fuel Economy & EV Range' started by srivenkat, Aug 31, 2020.

  1. srivenkat

    srivenkat Active Member

    Joined:
    Feb 28, 2011
    596
    91
    0
    Location:
    IL
    Vehicle:
    2021 Prius Prime
    Model:
    XLE
    Hi All,

    Sorry if these have been asked before. I hear there's a sliver of the battery that's reserved for use in the HV mode, which is used once the EV range is depleted. A couple of questions in this regard:

    1. If I select HV mode while there are still, say, 20 miles of EV range left, would the HV mode be more liberal with the usage of the battery when I am traveling at a low speed, or would the HV mode still limit itself to the same small sliver of the battery that it would have used if there were no EV range left?

    2. If I am coming down a long hill, would the regen limit itself to the normal HV mode sliver of the battery or would it continue to charge the battery until the full capacity is reached?

    Thanks in advance.
     
    bisco likes this.
  2. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,571
    48,862
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    2) coming downhill will continue to fill the battery, but it won't reserve it for ev mode. if you keep driving hv, it will eventually use it.

    1) something near the sliver, but idk exactly
     
    srivenkat likes this.
  3. Salamander_King

    Salamander_King Senior Member

    Joined:
    Nov 8, 2015
    10,958
    8,836
    0
    Location:
    New England
    Vehicle:
    Other Hybrid
    Model:
    N/A
    The answer is yes and no, depending on who you ask. There are some reports that HV mode in PRIME utilizes the bigger buffer of the traction battery than regular Gen4 Prius and results in better mpg under strictly HV mode. I myself did experiment and did not find that to be the case. Whether I have a full traction battery or 50% or --% (i.e. 0%) SoC, for my driving condition, it did not make any difference in mpg or use of traction battery SoC under strictly HV mode. I reported my result in other thread, but I don't have a quick link. If and when I find it, I will post it here.

    Answer to this question is unequivocally it will continues to charge the battery until the full capacity. I just did that experiment as well. Provided you have a long enough hill or a long enough drive to regen energy, depleted EV range "--" SoC can be replenished all the way to full WITHOUT using CHG mode.
    Read this thread: Battery Charging After Depletion? | Page 2 | PriusChat
     
    #3 Salamander_King, Aug 31, 2020
    Last edited: Aug 31, 2020
  4. Tideland Prius

    Tideland Prius Moderator of the North
    Staff Member

    Joined:
    Oct 2, 2004
    44,768
    16,017
    41
    Location:
    Canada
    Vehicle:
    Other Non-Hybrid
    Model:
    N/A
    jerrymildred and srivenkat like this.
  5. Salamander_King

    Salamander_King Senior Member

    Joined:
    Nov 8, 2015
    10,958
    8,836
    0
    Location:
    New England
    Vehicle:
    Other Hybrid
    Model:
    N/A
    I think if the SoC is replenished by a long hill regen, it can be reserved for future EV mode use. I may have to toggle the HV/EV switch to lock in the SoC at the time it is fully replenished. But I don't think regen replenished SoC is any different from CHG mode replenished SoC or for that matter wall charge replenished SoC. I know as a fact that under strictly HV mode, the car does keep the SoC very much steady with a minimal loss. For example, when I am heading to a city on a long trip, I usually try to keep the SoC for the destination. Starting with 100% SoC on the dash, driving strictly in HV mode for 300+ miles, I can finish the HV mode portion of the trip with 95% or more SoC left before switching to the EV mode in the city.
     
    Tideland Prius and srivenkat like this.
  6. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,571
    48,862
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    i know it will keep a wall charge, and charge mode charge. i haven't read of anyone refilling on a long downhill and experimenting with hv and ev. you could be right, the pip won't keep it unless you regen in ev mode.
     
  7. Salamander_King

    Salamander_King Senior Member

    Joined:
    Nov 8, 2015
    10,958
    8,836
    0
    Location:
    New England
    Vehicle:
    Other Hybrid
    Model:
    N/A
    It's not a long hill, and it's not a full charge, and not all the regen are strictly under HV mode, but "trickle" charged SoC using regen only from depleted EV range on my PRIME two days ago is still at 14%. I can keep this SoC for EV mode drive next week for sure.
    Battery Charging After Depletion? | Page 2 | PriusChat
     
    #7 Salamander_King, Aug 31, 2020
    Last edited: Aug 31, 2020
  8. Tideland Prius

    Tideland Prius Moderator of the North
    Staff Member

    Joined:
    Oct 2, 2004
    44,768
    16,017
    41
    Location:
    Canada
    Vehicle:
    Other Non-Hybrid
    Model:
    N/A
    Also, if you went from EV to HV then go down a long enough downhill to recharge EV range, it will be default back to EV.
     
  9. Salamander_King

    Salamander_King Senior Member

    Joined:
    Nov 8, 2015
    10,958
    8,836
    0
    Location:
    New England
    Vehicle:
    Other Hybrid
    Model:
    N/A
    That was what I thought. But on my recent experiment, EV to HV after EV range depletion and on HV regen to replenish EV range SoC, after 3% SoC appeared on the dash, it did not default back to EV mode. It stayed HV mode until I manually switched to EV mode. @CharlesH reported this phenomenon.

    I will have to try again with a long down hill next week.
     
    Tideland Prius likes this.
  10. jerrymildred

    jerrymildred Senior Member

    Joined:
    Oct 28, 2016
    11,490
    14,095
    0
    Location:
    Tampa, FL
    Vehicle:
    2017 Prius
    Model:
    Two
    Sure you have. You just forgot. Well, I'm pretty sure you did. I charged mine to 98% coming down a mountain in Colorado. Both the PiP and the Prime will lock in the charge level when you regen in either mode and then toggle the EV/HV ending up in HV. In other words, if you're in HV going down a big mountain, both cars will regen all the way down or until the battery is full or overheated. When you level out, put it in EV and then back to HV. That'll be the new level of charge it will maintain. If you're in EV coming down, just put it in HV and it'll hold that SOC. I did it in the Smokies with the PiP and the Rockies with the Prime. I've also done it a little at a time on flat roads using the same technique after braking for stop lights just as an experiment.
     
    bisco, srivenkat and Salamander_King like this.
  11. srivenkat

    srivenkat Active Member

    Joined:
    Feb 28, 2011
    596
    91
    0
    Location:
    IL
    Vehicle:
    2021 Prius Prime
    Model:
    XLE
    To make sure I am understanding this correctly, if you don't toggle to EV and then back to HV when you level out, the original continuing HV mode will use the entire energy regenned coming down the mountain, right?
     
    jerrymildred likes this.
  12. Salamander_King

    Salamander_King Senior Member

    Joined:
    Nov 8, 2015
    10,958
    8,836
    0
    Location:
    New England
    Vehicle:
    Other Hybrid
    Model:
    N/A
    Yes, that is what @jerrymildred is saying and I think he is correct on this as I stated in my comment above him. I will test if the toggling is necessary to keep the SoC or not. I will regen "--%" in EV SoC in HV mode next week on a hill near me that will give back ~30% of SoC on it's descent.





     
    #12 Salamander_King, Aug 31, 2020
    Last edited: Aug 31, 2020
    jerrymildred and srivenkat like this.
  13. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,571
    48,862
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    we don't have any hills around here, so i must not have paid attention to that one :cool:
     
    jerrymildred likes this.
  14. jerrymildred

    jerrymildred Senior Member

    Joined:
    Oct 28, 2016
    11,490
    14,095
    0
    Location:
    Tampa, FL
    Vehicle:
    2017 Prius
    Model:
    Two
    You are correct. Regenerating in HV going down a mountain that puts 10 miles back in your battery is treated by the car exactly the same as regenerating a half mile of charge stopping at a traffic light on a 50 mph highway. If you don't lock it in by putting the car into HV (EV and then HV is you were already in HV -- it HAS to go INTO HV to set the new level), then the car will use that excess charge to improve gas mileage while returning the battery to its previous level.
     
  15. srivenkat

    srivenkat Active Member

    Joined:
    Feb 28, 2011
    596
    91
    0
    Location:
    IL
    Vehicle:
    2021 Prius Prime
    Model:
    XLE
    A weird observation on a ~7 mile trip across town this morning: Battery at 53%. Placed in HV as soon as car switched on. ~80MPG (per short trip meter) over the 7 miles to the destination. Switched car off and then on; HV ASAP. ~112MPG (per short trip mater) over the 7 miles back home. How believable are these? How much salt should I take these numbers with?
     
  16. Salamander_King

    Salamander_King Senior Member

    Joined:
    Nov 8, 2015
    10,958
    8,836
    0
    Location:
    New England
    Vehicle:
    Other Hybrid
    Model:
    N/A
    A short trip like that is not very good indicator of the true mpg, but one explanation is that even if you switched to HV mode immediately after you started the car, the car probably used the traction battery to propel the car during warm-up cycle. During the warm-up, the engine is on, but most of energy used for propelling the car comes from the traction battery. Did you check your traction battery SoC after the 7 mile trip? I bet it wasn't at the 53%.
     
    srivenkat and jerrymildred like this.
  17. srivenkat

    srivenkat Active Member

    Joined:
    Feb 28, 2011
    596
    91
    0
    Location:
    IL
    Vehicle:
    2021 Prius Prime
    Model:
    XLE
    The SoC did fluctuate down to 50%, IIRC. But this is the case with other hybrids as well as they do propel using the battery during the initial warm-up, right and they never report numbers this weird, at least with the Gen III Prius and Gen I HyCam I have experience with. Either the computation is wrong (different on the Prime) or it's using a wider band of the battery for momentary EV under HV, it seems like.
     
  18. Salamander_King

    Salamander_King Senior Member

    Joined:
    Nov 8, 2015
    10,958
    8,836
    0
    Location:
    New England
    Vehicle:
    Other Hybrid
    Model:
    N/A
    It is possible that PRIME uses some stored EV portion of SoC on initial warm-up and beyond. That may contribute to the reported better than regular Gen4 Prius mpg in HV mode. I myself have not seen any of my HV only drive to show extremely high mpg over the longer drive (~40miles). In any case, mpg displayed on PRIME for such a short trip is very inaccurate for sure. For longer trips of more than 30miles, the dash mpg is usually close to what I see on the Hybrid Assistance App from via OBDII reading.
     
    srivenkat likes this.
  19. jerrymildred

    jerrymildred Senior Member

    Joined:
    Oct 28, 2016
    11,490
    14,095
    0
    Location:
    Tampa, FL
    Vehicle:
    2017 Prius
    Model:
    Two
    It's been my observation that it does eat into the SOC quite a bit during warmup. If your trip is done before it pays all that back, you can get some pretty astonishing MPG numbers. Once it's warmed up, when driving at 50 mph or so, it'll still put itself in EV and take from the EV range for about 2-3% SOC and then pay it back by running the ICE. The more cycles of that it goes through, the less effect on trip mpg it'll have. So it's negligible on a 150-mile trip but significant on a 10-mile trip.
     
    srivenkat and Salamander_King like this.
  20. Tideland Prius

    Tideland Prius Moderator of the North
    Staff Member

    Joined:
    Oct 2, 2004
    44,768
    16,017
    41
    Location:
    Canada
    Vehicle:
    Other Non-Hybrid
    Model:
    N/A
    Also keep in mind that 3% of the Prime's SOC is quite a bit.

    3% x 5.5kWh (usable SOC) = 0.165kWh used (it's a low ball since you would've charged a bit during the engine warm-up cycle so you probably rose to 54 or 55% but since we don't know, we'll ignore it for now)

    Gen 4's Li-Ion battery is 0.745kWh (equivalent to the NiMH's 1.3kWh so I'll use the Gen 4's Li-Ion chemistry). SOC ranges from 10% to 80% (roughly... from 0 bars to 8 bars on the battery meter). So 70% of 0.745kWh = 0.522kWh of usable battery in a Gen 4.

    0.165/0.522 = 0.316 or ~ 32% of the equivalent Gen 4's battery. (again, this is low because we didn't account for the extra engine top up).

    So basically it's as if during the trip, you somehow managed to go from 6 bars to 2 or 3 bars (or 8 bars to about 4-5 bars) which in a regular Prius is essentially "draining" the battery to boost mpg numbers.

    So, yeah I can see that. One time I got 84mpg (2.8L/100km) in HV mode on a one way trip that included a short highway portion (50mph) and a bridge but I activated CHG mode and got enough charge to go into EV mode for the last portion of the trip after I exited the highway (about 3 miles).