Question about battery charging while on the go

Discussion in 'Prime Plug-in Charging' started by ihf, Sep 7, 2021.

  1. ihf

    ihf New Member

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    I have a new 2022 Prius Prime and I have a question about something the salesman said and which seems to be confirmed by some posts here in the forum but which I am having trouble with. My understanding is that the traction battery which drives the electric motors is recharged while by the gas motor as well as through regenerative braking. I also read that when the battery drops below some threshold, the car will no longer use EV mode but will use Hybrid mode (as in the non-PHEV model). If the car is capable of charging the battery above the threshold, does it then go back to EV mode and thereby deplete the battery back to the threshold and so on. If so, it would seem that you can’t really ever charge above the threshold since it will always go down when you go back to EV. What am I missing here?
     
  2. Tideland Prius

    Tideland Prius Moderator of the North
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    If you are in hybrid mode and you regen above the threshold (e.g. went down a short, steep slope or a long gentle one) and you actually gain enough charge for the car to show a % remaining in the EV section (or EV miles, depending on your personal setting), then the car will go back to EV mode until that extra charge is used up.

    If you wish to save that charge, you could switch back to HV mode and the car will save that as the new threshold until something changes (e.g. you charge the car or you go back to EV mode to use up the excess charge).

    If you wish to force charge using the engine, press and hold the EV/HV button until "CHG" appears on the instrument panel. Now, the engine will rev higher and charge the battery up to 80%. Of course your mpg will suffer but if you need some extra charge (e.g. you're on the highway and want some extra charge to drive in EV mode when you get into the city centre; or it's a hot day and you want to be able to pre-cool the car using the battery, you need some charge in the battery to do so).
     
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  3. ihf

    ihf New Member

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    Thanks that helps but I am still not completely clear about how you “save that charge”. If we assume for this discussion that the normal EV threshold is 20% (I’ve no idea what it is), and through regen it goes to 21%, will the car immediately go to EV mode and bring it back to 20%. If so, how could you ever get above the threshold and thereby have any charge to save?
     
  4. ihf

    ihf New Member

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    Unless of course, you are able to add charge faster than you use it.
     
  5. bisco

    bisco cookie crumbler

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    'you can't ever charge above the threshold' is a contradiction. just because you charge above the threshold, then use that up in ev and go back to hybrid mode doesn't mean you didn't charge above the threshold.
    in practice, unless you live in a mountainous area, you won't find it charging back above the threshold very often. it takes a lot of regeneration.
    most of your ev will come from plugging in, unless you want to use force charge for some reason.
     
  6. Tideland Prius

    Tideland Prius Moderator of the North
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    It's called "stacking".

    Using your thresholds for discussion, let's continue your scenario.

    It goes to 21% and goes to EV mode automatically, you press the EV/HV button to return to HV mode, the car now uses 21% as the new threshold as it does it's HV duty (charge/deplete etc). Let's suppose you go down another hill or do a long slow brake and now the SOC is at 23%. You press EV/HV to switch to EV mode, then press EV/HV to switch back to HV mode. Now, you've set the new threshold to 23%.

    Basically, any time you switch from EV to HV mode, the car will try and maintain the battery level (just like a regular Prius does). The only difference is that threshold isn't necessarily always at the HV/EV default threshold (20% in our discussion). For clarity, let's say you had a fully charged car and you used some battery. Now it's down to 60% but you switch to HV mode. The car will now use 60% as the new threshold and will use some charge and top it back up and try and hover around that SOC.
     
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  7. ihf

    ihf New Member

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    Thanks. This was meant to be largely a hypothetical discussion to help me understand how the charging of the EV battery works. But here is a potential scenario for wanting to "preserve" the charge available for EV driving. Imagine I am driving 50-100 miles to a location (e.g. NYC) where charging the car is not so easy and I would like to run in EV mode while in the city. If I charge the battery fully before leaving, can I set the threshold at 100% such that the car will only run in ICE mode and not delete the battery? Or if I forget to charge the battery fully before leaving could I use the force charge to top off the EV battery to use while in NYC?
     
  8. fed123

    fed123 Member

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    Living outside NYC I am often in this exact position. I charge up the battery, drive into NYC in EV/HV mode, and then when I get to NYC I switch back to EV or EV/Auto to use the battery.

    When I am ready to come home I switch back to EV/HV until I get home so I can have some battery tootering around my home town.

    SM-P610 ?
     
  9. vvillovv

    vvillovv Senior Member

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    There is also Charge Mode. When the battery goes below the threshold ie: your %20 estimate above, you can go into charge mode by pressing and holding the EV/HV button for 5 seconds. The EV mode green indicator next to the speedo will switch to Charge Mode.
    Than the gas engine will charge the battery to it's upper threshold of %80. That typically takes about 45 minutes from the bottom threshold, ie: your %20 above. Than when battery reaches the upper threshold of %80 the car switches back to - HV (I think) I haven't used Charge Mode in a while so I've forgotten when mode it switches back into. You have to watch the gauges to switch to whatever mode you want to be in if the car automatically switches into a mode you don't want to be in, and it's possible to switch into the mode you want to be in , which it's not always possible, especially near the thresholds.

    The best way to learn about how the car works is to find what you like to use and practice at using it.
     
  10. jerrymildred

    jerrymildred Senior Member

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    The method is the right one. But to clarify terminology, there is no such thing as "EV/HV" mode. The EV/HV button toggles between EV and HV modes. It's one or the other.

    Just hit the EV/HV button to put it in HV mode as soon as you start it. The indicated percentage of charge may go down and back up a few percent as you drive since the car uses the battery in hybrid mode just like any other Prius. If you have big hills that you'll be going up and down on the way to the city, you may want to use enough charge before the hills (maybe 10%) to absorb the regeneration going down them, but they'd need to be pretty long downgrades before the Prime would have to use engine braking, even if the SOC was 100%.

    Of course. It's kind of a gas waster. It's cheaper to let the car decide when to charge or use the battery, but you can do that. At city speeds, the Prime will drive for quite a long distance in HV mode with the engine off. Then it will charge the battery back up and then go back to engine off all by itself. It's incredibly efficient.
     
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  11. fotomoto

    fotomoto Senior Member

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    Back in 2013 (seems so long ago.....), I discovered this ability in my C-max Energi. I like to call it “EV banking”. I think it’s a better term for what the operator is trying to achieve. I have no hills so I employ EV banking during high-speed braking to a stop.

    On my typical 90 mile out of town round trip, I can pick up 5-6 EV miles. It’s only 4 urban miles from the interstate to my house so I use those “free” miles on this final leg which also gives the ICE time to cool down before I pull into the garage (NICE!). Remembering to switch back/forth between EV and HV modes is the tricky part.
     
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  12. Salamander_King

    Salamander_King Senior Member

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    When the electricity rate was higher than gas price (not too long ago when gas was below $2/gal), I was using the gas engine on HV mode on all the uphill and accrecelation and switching to EV mode on all the downhill and coast/deceleration to use regen to stock up on the battery charge. I went on not charging my battery for months but always had some charge left in the battery for EV mode when needed.
     
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  13. ihf

    ihf New Member

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    Does anyone know how much gasoline is used to recharge the battery from a depleted state to fully charged using the CHG mode?
     
  14. Old Bear

    Old Bear Senior Member

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    It's a good question. However, I believe that CHG mode will only bring the battery to 80% before automatically returning the Prime to EV or HV mode.
     
  15. Salamander_King

    Salamander_King Senior Member

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    As stated above by @Old Bear, CHG mode can not bring the traction battery full. Only up to 80%. But, I don't remember anyone actually measuring the amount of gas needed to bring 0% to 80%. Most of the time, CHG mode is operated while driving, so it negatively affects (lowers) MPG. But the MPG numbers displayed (or calculated) do not tell the exact amount of gasoline used for charging the traction battery since it includes the actual driving part which can be affected by many factors.

    It is easy to measure this by using CHG mode whiled parked. Use CHG mode to bring the EV depleted battery to 80% while parked, and check the amount of gas used by the full tank method. Humm, I don't see CHG mode being cheaper than using the wall charge especially now gas price is higher, but I am very curious to find out this. I may try doing this experiment myself.
     
  16. jerrymildred

    jerrymildred Senior Member

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    I suspect that variations in where the pump clicks off from one fill-up to the next, would make this pretty inaccurate. You'd probably need to average a bunch of tests. But aside from having a test rig to feed fuel from an external measured container instead of the gas tank, it's probably the best way to attempt it.

    I'm content to know that with the price of my electricity even before solar power and the price of my gas, wall charge is WAY cheaper electricity than charge mode.
     
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  17. ihf

    ihf New Member

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    I don’t know how much more gas CHG mode uses than average driving but if you use 50 mpg and travel the 25 miles that you would get in EV mode, that would be a half gallon of gas. Around here a half gallon of gas is a little over $1.50. If I assume that I am charging the battery from 0% to 80%, I believe that would be approximately 7KWH. I pay approximately $.20 for a kilowatt hour. Therefore using these very rough numbers the cost of charging it with gas versus electricity is about the same.
     
  18. Salamander_King

    Salamander_King Senior Member

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    Yes, I see your point. After doing the math, it may not be so practical to try this experiment.

    Knowing 80% charge of the traction battery is only ~5kWh of electricity, using EPA's formula, in which 33.7kWh of electricity is equivalent to one gallon of gasoline, I can estimate the single 0-80% CHG mode will use ~0.15 gal of gas (5kWh÷33.7kWh/gal). With some loss in the conversion, the actual amount is probably higher than 0.15gal. You are quite correct that I would need at least half a tank worth of gas used for the CHG mode to get a more accurate average number. That would be over 30 CHG mode (0-80%) charges and each charge has to be depleted without using gas on HV mode in between the CHG cycle. Hard to pull off as I do regular driving of longer than 25miles.
     
    #18 Salamander_King, Sep 10, 2021
    Last edited: Sep 10, 2021
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  19. dig4dirt

    dig4dirt MoonGlow

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    @john1701a did a video long ago on a 2017 Prime

    Roughly 40mpg on dash for 0-80% in charge mode

    CHG MODE
     
  20. Salamander_King

    Salamander_King Senior Member

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    The full charge on the battery is less than the full capacity of the battery which is 8.8kWh. The actual full charge from the wall is somewhere around 5.8-6.8kWh and the actual usable charge in the battery is about 5.4-6.0-kWh. The precise number of this "usable" capacity has not been disclosed by Toyota, and various owners of PP have attempted to estimate it with some variations. But it is most likely to lay somewhere in that range. So 80% charge is likely to be 4.4-4.8kWh.

    Your electric rate is similar to mine. I pay $0.21/kWh. At this rate, when the gas price is below $2.85/gal, it is cheaper to drive using gasoline on HV mode. If the CHG mode conversion is lossless, then your assumption is correct that at your electricity rate and assuming $3/gal gas price, CHG mode gas will cost roughly the same cost as using wall charge. But be reminded that using CHG mode to charge the traction battery will not save you any money. It is cheaper to drive purely on HV than using CHG mode at any instance. Purely for an economical term, PHEV or BEV makes no sense in our high electricity rate area, but if your grid electricity is cleaner like mine, 100% renewable, then using less gas more electricity makes some contribution albeit minuscule in combatting the global climate change problem.
     
    #20 Salamander_King, Sep 10, 2021
    Last edited: Sep 10, 2021
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