How fast HV without battery capacity decline

Discussion in 'Gen 1 Prius Plug-in 2012-2015' started by CraigCSJ, Feb 14, 2012.

  1. CraigCSJ

    CraigCSJ Active Member

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    On page 93 of the Prius PHV Owners Manual, under the heading "Capacity reduction of the hybrid battery (traction battery)" is the following language:

    "By observing the following precautions, battery charge decline can be suppressed."
    "Avoid driving near the top speed for EV driving ( --P.40)"

    To me this says don't drive EV 60 MPH, don't drive EV 55 MPH, maybe 50 MPH is OK is not uphill, probably 45 MPH is OK.

    The manual also says "Also, if the hybrid battery (traction battery) capacity reduces, the EV driving range decreases. However, vehicle performance does not significantly become worse."

    I wonder if this is a statement that the warranty will not cover capacity decline?

    Several weeks ago I passed a Volt going about 50 MPH on a highway with maximum speed of 65 MPH. The highway was four lanes, straight, trending down, and immediately after a steep, mountainous down slope. The Volt would have generated considerable electricity on the down slope, but why was it going only 50 MPH? Was it to slow battery capacity decline?
     
  2. usbseawolf2000

    usbseawolf2000 HSD PhD

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    The rate of power drawn from the battery is higher at faster speed. You get lower EV range, the faster you go. That's why we see a lot of Volt owners driving around 50 MPH. Volt's full battery would be drained in 15 mins at 85 mph.

    For Prius PHV, the battery could be drained in 10 mins at 62 mph. You'll get about 10 miles EV range. If you driver slower in EV mode, you could get 15 miles or more.

    Use the battery at lower speed and gasoline at high speed. If your trip is short and consist of mostly highway, use the battery on the highway as well.

    As for the capacity and performance statement, I think they meant 0-60 won't suffer significantly if the battery doesn't hold as much charge (after 10 years warranty?).
     
  3. john1701a

    john1701a Prius Guru

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    That's a round-about way of saying EV at high speeds will drain the pack quickly, so save it for suburb & city driving instead.
    .
     
  4. CraigCSJ

    CraigCSJ Active Member

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    I believe these statements in the Owners Manual refer to the capacity of the traction battery, which will decline over time. I believe the Manual is telling us to avoid these things if we want to slow down the decline in capacity. For instance, I believe it is telling us that if we often go 60 MPH in EV mode, we will sooner find that the traction battery will not hold as much charge as it did when new - like if when new it would hold enough electricity to go 15 miles at 40 MPH, later it would only hold enough electricity to go 10 miles at 40 MPH.

    I encourage you to read the page referenced. I hope you are right in your interpretation of this wording, and I know how sometimes ideas get confused when going from Japanese to Engilsh.

    There are two other things in this same group to avoid: 1) Leaving the car in the sun on a hot day with the battery fully charged, and 2) Leaving the car sit for a long time with the battery at full charge.

    These tell me that the stated things should be avoided to slow the capacity decline, not the rate of decline when fully charged.
     
  5. Paradox

    Paradox Prius Enthusiast / Moderator
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    Did you mean EV in that statement instead of HV? I seriously doubt the battery packs capacity will diminish from driving highway speeds in HV mode.
     
  6. drash

    drash Senior Member

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    I thought the battery pack will help out at any speed if left in HV mode and there is a lot of EV range left.
     
  7. Paradox

    Paradox Prius Enthusiast / Moderator
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    People in this thread are looking at the word capacity in different contexts.

    What I meant is this.

    Craig said
    I take it he means the the battery will, over time, not hold as much capacity as it did when new if driven at highway speeds in HV mode.

    I think he means EV mode. I can see Toyota after all these trials witnessing that if the car is driven at say 60mph for several miles in EV mode, the heat the pack generates over time reduces overall battery capacity.

    Answering your question, yes, the battery pack will help out at any speed when in HV mode and there is a lot of EV range left. Even if no EV range is left, the cell which is for HV will help out at any speed same as a 'regular' Prius.
     
  8. Paradox

    Paradox Prius Enthusiast / Moderator
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    People in this thread are looking at the word capacity in different contexts.

    What I meant is this.

    Craig said
    I take it he means the the battery will, over time, not hold as much capacity as it did when new if driven at highway speeds in HV mode.

    I think he means EV mode. I can see Toyota after all these trials witnessing that if the car is driven at say 60mph for several miles in EV mode, the heat the pack generates over time reduces overall battery capacity.

    Of course the battery pack will help out at any speed if left in HV mode and there is a lot of EV range left.
     
  9. CraigCSJ

    CraigCSJ Active Member

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    Yes, and I corrected my post. But couldn't correct the title which should read EV, not HV.

    Toyota may also be saying that leaving the traction battery at high charge reduces overall battery capacity. In the Manual, Toyota says when leaving the vehicle undriven for long periods to leave the charge low; and that the owner should use the timer to fully charge the traction battery just before using as much as possible.
     
  10. iRun26.2

    iRun26.2 New Member

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    CraigCSJ, I think you made a very good catch. If this is true (driving at 62MPH in EV mode will tend to reduce future full-charge battery capacity), we will need to be more careful how we drive.

    This somehow seems a little odd because, in the non-plug-in Prius models, the user was basically pretty much protected by the car's firmware from doing something foolish (like nearly depleting the battery of all charge).

    If true, it is very interesting that Toyota would allow you to drive in ways that are detrimental to the battery's health. Maybe it is just a fact of life that can not be ignored. Maybe it won't be too bad, but if it wasn't, why would they mention it?

    It certainly makes me wonder what warranty battery replacement will be based on.

    It will add one more little nuance to driving the PHV, that's for sure! (I could accept only getting 5 to 8 miles from EV driving at 62MPH, but if this drops my overall maximum charge capacity, I will not drive that way simply for the best health of my PHV battery).
     
  11. daniel

    daniel Cat Lovers Against the Bomb

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    No manufacturer gives a warranty on the rate at which battery capacity declines over time. (Though some people read the rather confusing Volt warranty to disagree with this statement.) Regular Prius is free to use or not use the battery, as the computer determines best, and therefore can protect the battery, at the cost of lowered FE under less than ideal conditions such as cold weather. The PiP is supposed to be capable of EV operation, so you get into an area where the computer has less control.

    There are a number of strategies the programmer can use to help protect the batteries, but with any EV there are things the driver can do to increase or decrease relative battery life. My car has a "Storage" mode, for use when the car will not be driven for longer than two weeks. In this mode, the battery charge is kept around 1/2 to 1/2 full. I can also choose Performance mode, which raises the battery temperature for faster acceleration at the cost of reduced battery life.

    But I wonder if the passage cited in the OP refers to battery degradation over time, or merely the reduced EV range at high speed. Any car will have reduced range at high speed, but the PiP has such a short EV range that this will be more noticeable. Once you excede the EV speed, the ICE comes on, and your battery charge is saved for later, or used more slowly.
     
  12. drash

    drash Senior Member

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    Yep. Typical of all rechargeable batteries to leave the battery stored in a partially discharged state. Leaving it at high charge has rather dramatic effects if combined with being left in the summer sun for a week at the airport. There's no room left for expansion in the heat.

    As for the timer, Toyota is merely suggesting that if you use a timer, it'll give the battery pack a chance to cool down between charging and discharging.
     
  13. drash

    drash Senior Member

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    Many of these suggestions are for our more southern based fellow Americans who have the benefit of free heat for most of the year (ok sometimes it too much of a good thing). Lithium ion batteries really do not tolerate heat well. I'll probably pay more attention to these suggestions as the sun climbs higher in the sky. For the other 9 months I may actually micro-cycle the battery more as the temps dip.
    :D
     
  14. iRun26.2

    iRun26.2 New Member

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    What do you think about the notion of Toyota 'allowing' us to now drive the car in EV mode at 62MPH yet saying that it may 'reduce the battery capacity' (maximum charge capacity may go down prematurely)?

    Is heat the issue here too? I had hoped to drive at close to 60MPH on my commute but if it is bad for the long term health of my battery then I won't (but that would be almost slightly deceitful on Toyota's part to claim 62 MPH in EV mode if they say not to use it).
     
  15. drash

    drash Senior Member

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    Heat yes. They are being cautious because they don't know where you will drive it and the fact is, Toyota is air cooling the battery. So if you drive at that speed, a lot, on EV mode in the Sonora or Mohave desert in the summer at 2:00 in the afternoon with little or no A/C, then yeah, your capacity will diminish over time faster than others. Of course with the A/C on this effect will be immediate but not permanent. ;) All batteries will diminish with time and this heat effect is even more pronounced on large area batteries (and even more so in fuel cells). Also this is lawyer speak put in to relieve themselves of liability issues.

    Which brings me to a pet peeve. Why in heavens name didn't they just put in the solar roof and raised the price $1000? IMHO would have easier on the battery in the long run. Heat kills.
     
  16. sxotty

    sxotty Member

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    High C-rate heats up the pack from internal resistance of the cells regardless of external temperature.
     
  17. andi1111

    andi1111 Member

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    It does, but it still differs if the pack ends heating at 40°C or at 60°C (with staring temperature being 20°C higher).
     
  18. daniel

    daniel Cat Lovers Against the Bomb

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    I'm not at all sure that they're saying it will shorten battery life. They may be saying that the SoC will drop faster at high speed.

    The roof of a car is a very inefficient place to put PVs. Not enough area, most of which is pointed in the wrong direction, and most cars get parked in the shade much of the time. You just wouldn't get much cooling power from a solar roof. What a solar roof can do is operate a fan to bring external air into the cab when parked in the sun.
     
  19. seilerts

    seilerts Battery Curmudgeon

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    Regardless of what they intended, both statements are correct. It takes more Watt-hour/mile at higher speed, and higher average current draw leads to shorter lifetime.
     
  20. usbseawolf2000

    usbseawolf2000 HSD PhD

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    Regardless, the battery pack must be designed to last 10 years / 150k miles to cover the warranty. Toyota doesn't design to die at warranty period. They normally make sure it can last 2-3x the warranty miles.
     
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