Charge-Mode for Prius Prime

Discussion in 'Prime Technical Discussion' started by john1701a, Aug 9, 2017.

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  1. john1701a

    john1701a Prius Guru

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    Wisely used, the choice to consume EV miles generated by the gas-engine rather than from plugging in can result in an efficiency gain. Poorly used, the resulting MPG will be lower.

    In most cases, you are better off just using plug-supplied electricity. However, I have discovered on long highway trips with my Prius Prime and no place to plug in, it can be handy to take advantage of charge-mode.

    This video footage is a capture of the complete charging cycle, presented at 15 times normal speed. Pop-Up of the DRCC (Dynamic Radar Cruise Control) is usually a pleasant visual experience; the car automatically slows down upon detecting a slower vehicle ahead of it. At this speed, the display can be a bit disruption. So, pause the video from at times to see detail.

    Overall efficiency, including acceleration onto the highway and deceleration to exit afterward, was 40 MPG. That's incredible considering the A/C was at the coldest setting (that's "LO") with the blower on medium the entire time. This caused the recharge to take 10 additional minutes, but 50 minutes is much faster than when plugging in anyway.

    Watch the video careful. Keep in mind that brief recharging is likely what you'll end up using, not the entire 80%. When you do, choose wisely.

     
  2. fotomoto

    fotomoto Senior Member

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    So it took 50 miles to reach 40mpg. How would you describe the topography (hills, level, etc)?

    Interesting. Why?
     
  3. john1701a

    john1701a Prius Guru

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    Without A/C, back in the spring, it only took 40 miles... more electricity for charging.

    As for the driving, there were hills, people cutting me off, construction slow down... a wide variety... hence letting DRCC entirely handle pedal control.
     
  4. stevepea

    stevepea Senior Member

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    First of all, interesting, thanks for posting this.

    However, I did a bit of quick math (not exact, just general) and here's what I came up with, living in SoCal where I do:

    Choice #1: Put the car in "Charging Mode" while driving as you did:
    It took you 1.25 gallons to go that 50 miles (50mi/at barely 40mpg). At $2.80/gal (about the price in the area recently) that's $3.50 worth of gas to go those 50 miles and have your car charged 80% full.

    Choice #2: Only use normal HV (no charging while driving). I'm going to estimate 60mpg which I think is pretty fair for 50 miles of steady driving (no sudden accels, etc). So if one doesn't charge, it would use 0.83gal. At the same $2.80/gal, that would have used $2.32 worth of fuel. To charge at home (to the full 100%, not 80%) costs me about $1.17 (16c/kwh rate) each time (between $1.15 - $1.20).

    So...
    (1) Driving 50 miles using the charge mode -- and getting only an 80% charge -- costs $3.50.
    (2) Driving 50 miles using only HV and then plugging in -- and getting a full 100% charge -- costs $3.49.

    Using these figures, it's about the same cost, but plugging in at home gives you 100% charge vs only an 80% charge.

    Again, this is only quick, general math, not exact, and everyone's gas/electric prices will vary, but I see the charging mode still being less efficient/costing more. Please don't misunderstand: I really liked your post -- thanks for posting it, it was quite interesting. I suppose there might be times to want to use the charging (as Bob mentioned elsewhere, if you're running out of gas, perhaps) but as far as efficiency, at least using the prices for gas and electricity in SoCal here, it seems to be more costly than just plugging in and charging normally, even under the best of circumstances.
     
  5. john1701a

    john1701a Prius Guru

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    Do not overlook this important comment, which influences consideration of use: no place to plug in

    When you are out on vacation, there can indeed be a benefit from having some EV available. Rather than going through the warm-up cycle, you can avoid HV entirely. Under some circumstances, that will result in higher overall efficiency. For example, going out in the morning for breakfast. The engine is cold and you only need it for a brief time. EV could easily cover that real-world circumstance.

    Also, there was the concluding comment about briefly recharging: not the entire 80%

    It is unnecessary to recharge as much as possible. Just a little will do. Choose wisely.
     
    #5 john1701a, Aug 10, 2017
    Last edited: Aug 10, 2017
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  6. jerrymildred

    jerrymildred Senior Member

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    That's where I see the most potential benefit from charge mode. Thanks for the experiment.
     
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  7. NJ-PrimeAdvanced

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    Excellent post and thanks for doing this analysis... this shows that using CHG mode while driving on a regular basis is great... especially for the many folks (like me) who can not charge at home. I enjoy driving in EV mode and the only way for me to enjoy it is by using CHG mode and the occasional free charging station on the way.
     
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  8. stevepea

    stevepea Senior Member

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    NJPA, I still see the charge mode as not being as efficient (at least with my costs here in CA), as for about the same price you only get an 80% charge not 100%. I suppose if there's no place to plug in for multiple days and one likes driving in EV Mode and doesn't mind paying a bit more, it's certainly an option.

    John, perhaps only under the scenario you mentioned (a very short drive the next morning for breakfast, avoiding the warmup cycle) -- though in order to have a small charge for such a scenario, you'd have to know the day before to do a small charge so you'd have it for the next morning. But if you were to know it the day before, the more efficient solution would simply be to switch off the EV a few miles before the range runs out, so you have a few miles the next day for breakfast. The only scenario that makes sense is if you're doing perhaps a few days in a row without using EV, (more than 1 day) in which case the scenario might make sense.

    But in general, if you're planning ahead anyway (thinking about charging for later), I just shut off the EV with a tiny bit of range left instead. For example, there's a commute I do about 7 times a year. It's 50 miles each way (100mi round trip). Near the end of the "going there" direction, there's a very steep, long uphill grade (and thus, near the beginning when it's time to "go home", there's a very steep, long downhill drive). Now since it's 50mi each way, that's further than my EV Range (I'd have to use HV at some point anyway) -- but I make sure to switch off the EV with about 2 miles left to spare... because when it's time to go back home, I want to be able to do that nice downhill grade in EV (using "B" to charge the traction battery) instead of having to do it in HV (with some charging, but a lot of it wasted). If I've used all my EV charge going there, I won't be able to be in EV Mode for that downhill grade on the way home, and because the steep grade is right at the start of my "going home" direction, there wouldn't be time to use charge mode to give enough to get back into EV mode even if I wanted to. So I simply turn off the EV myself about 2 miles earlier than when the car would do it on the way there, so when it's time to go home that nice long downhill is put to the best use for charging: going down a steep hill in "B" while in EV Mode (and with the nice charge from going downhill in EV-B Mode, I then have a bit of EV range at the bottom of the hill before the HV has to turn on).

    I know I'm being critical here, but I really do appreciate your post and the time it took for those figures. All good stuff to know.
     
    #8 stevepea, Aug 10, 2017
    Last edited: Aug 10, 2017
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  9. john1701a

    john1701a Prius Guru

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    @stevepea, no problem.

    Most people haven't had an opportunity to take a long driving vacation in their Prime yet. So the using up EV, even when judicially consumed and not having a plug available for recharge, simply hasn't come up yet.
     
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  10. NJ-PrimeAdvanced

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    Has it been confirmed/proven that when going downhill, EV-mode+B-mode switched on the same time is the best case scenario for the maximum regen/charging? I read in other threads, that doing ACC when going downhill set at a lower speed gives you the best regen...
     
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  11. Trollbait

    Trollbait It's a D&D thing

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    The regenerative brakes are able to recapture the same amount of energy regardless of brake pedal use, which gear the car is in, or cruise control use. They all have the potential of netting the max amount. Which works best for an individual will come down to their preference.
     
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  12. NJ-PrimeAdvanced

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    Right... but if so, then why use the B mode? just apply the brakes .. is there any advantage of doing the B mode if the brakes will regen at the same rate whether B mode is in use or whether not? Maybe cos you get extra engine braking which means you don't have to touch the brakes so it's an easier ride downhill?
     
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  13. priuscatprimeguy

    priuscatprimeguy Senior Member

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    saves on wear and tear of the brakes?:D
     
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  14. Trollbait

    Trollbait It's a D&D thing

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    As long as the battery isn't near full, B gear will use just the regen brakes; no engine braking. this means when the accelerator is let off, more regen braking than with the same situation in D gear. Now the driver can apply the brake pedal slightly and get the same level of regen as in B.

    Either method will net the same result. So neither is better than the other. As I said, which one that works for the individual is just preference.
     
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  15. jaqueh

    jaqueh Active Member

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    I always make sure to switch it to ev mode before putting it in B. Does engine braking not turn on if there’s space in the battery even in HV mode?

    I like b mode a lot because unlike in the gen 2 (with cruder brake pedal feel) it’s pretty difficult to tell when the friction brakes are being used vs regen only. This was always a criticism that auto journalists lobbed at early hybrids, but I believe that the car has been made worse by having the more seemless transition between friction and regen.
     
  16. Tideland Prius

    Tideland Prius Moderator of the North
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    Excellent discussion. Yes, the Prime definitely allows the driver to choose how to best use the available features to suit their driving scenario. As long as we keep sharing ideas on how to use CHG or HV/EV (and EV Auto but not much talk about that), it can give other owners ideas on how to best customize the use of CHG, EV or HV to suit their needs and the type of experience they want out of the ownership of the car.

    Thanks guys!
     
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  17. wb9tyj

    wb9tyj 2017 Prius Prime Advanced

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    will be doing a quasi long trip...in mid august down to Alabama from Indiana...will experiment with the modes and log my results...This trip will entail Interstate roads, US highways, City Driving, and sitting around in ready mode during eclipse...My big road trip will be spring as our usual Indiana to Nevada run will be the good test...Interstate, US66, mountains and high desert...Getting my charge point and Greenlots accounts current...
     
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  18. I'mJp

    I'mJp Active Member

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    I've gotten to do two long round trips from central Massachusetts to central Arkansas and back.
    One way is about 1440 miles, ~ 23 hours

    My usual electric range is 34 miles, and while traveling I like keeping a 20 mile "electric reserve".
    It leaves a potential charging capacity of 14 miles, for some of those Virginia and Tennessee down hill regenerations.

    I used hv mode while on the highway, and charge mode until getting the 20 mile ev range.

    I used electric mode any time off the highway.

    On my first round trip, I kept the cruise control on the highway at 76, and averaged 48 mpg (per instrument panel).
    My wife was with me, and we did 3 - 8 hour shifts(one way), and the temperature was about 90F

    On my second trip, I set the cruise control at 69, and averaged 56 mpg for the entire ~3k miles.
    I was solo, and drove in 2 - 12 hour shifts(one way), average temperature 88F

    Eco mode on the air conditioner, temp set 73, and on the whole time.

    The car performed like a champ, and maintained the cruise setting despite the hills along I 84, 81 and 40.

    I'm completely satisfied with the performance of the vehicle.
     
  19. NJ-PrimeAdvanced

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    Great! would you say it's the best car you ever owned? Many folks think so.
     
  20. I'mJp

    I'mJp Active Member

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    I do indeed.
     
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