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No Percent Charge Option, Right?

Discussion in 'Prime Main Forum (2017-2022)' started by mr88cet, May 31, 2017.

  1. mr88cet

    mr88cet Senior Member

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    Like many of us it appears, I'm getting considerably greater range than the EPA-estimated 22-25 miles per charge.

    That then raises a question that I didn't expect to face: How can I charge to, say, 80%? As far as I can tell, there's no automated means of setting a charge limit, true? As far as I can tell, the only way to get it to stop at 80% is to pull the plug, literally, on the charge.

    80% would be enough to get me to work, would save a little on the power bill (not a big concern, but something), and would also somewhat improve battery life.


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  2. Lee Jay

    Lee Jay Senior Member

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    You can stop the charge manually without pulling the plug if you started it with chafe now just by turning off charge now. I've done it. But a charge to 80% and stop function doesn't seem to be available. I'd use it if it were.
     
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  3. mr88cet

    mr88cet Senior Member

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    Yeah, me too. I guess, with an 8.8KWh battery, they didn't expect anything but a full charge to be of interest.

    Relatedly, I wish there were a remote stop-charge button on the app.


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  4. Lee Jay

    Lee Jay Senior Member

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    I still haven't signed up for Entune or Safety Connect, so I haven't used the app.
     
  5. john1701a

    john1701a Prius Guru

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    That is already part of the design. It automatically stops.

    85% is maximum charge. 15% is left for untouched for battery longevity.
     
  6. Lee Jay

    Lee Jay Senior Member

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    And 70% of maximum charge will extend battery longevity even further. I consume about 50% of charge getting to work and about 15% getting home. Why not extend battery life?
     
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  7. mr88cet

    mr88cet Senior Member

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    No, I mean additional margin.

    I'm sure they designed in some margin, yes, but how do you know it's 15%?


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  8. john1701a

    john1701a Prius Guru

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    Charging Stations report how much electricity was delivered. A full recharge only takes roughly 6.5 kWh (stored in battery, plus charging losses), well short of the 8.8 kWh capacity.

    If you want greater longevity, allow the battery to cold-soak as much as possible before the charging starts by taking advantage of the timer scheduling. Also, keep it out of the extreme heat.
     
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  9. mr88cet

    mr88cet Senior Member

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    OK. Timer charging I can, and generally do, do, but I can only so much I can do about temperature...

    How much capacity at the bottom -- the "empty" end -- do you believe there to be? It's likely they reserved for hybrid operation roughly the same amount of capacity as a regular Prius, which I think I recall is around 0.8KWh. Presumably, there is some buffer below that too.

    If the low-end buffer plus hybrid-operation parts of the battery together constitute 1.2KWh (just a guess), then that plus the 6.5KWh you cited for a charge to full, would add up to 7.7KWh out of the 8.8KWh, or around 12%. That is indeed on the order of 85%, as you suggested, although those low-end numbers are largely guesses.


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  10. bisco

    bisco cookie crumbler

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    how would it save on the power bill?

    is there some kind of commercial timer you can plug into, that would allow you to shut it off at the wall?
     
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  11. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Let me suggest these solutions:
    1. Measure rate of charge per hour for L1 and L2 charging and total:
      1. BMW i3-REx: 5%/hr (L1); 20%/hr (L2); 100% @18 kWh
      2. Prius Prime: ~20%/hr (L1); ~50%/hr (L2); 100% @6.4 kWh
    2. Dumb EVSE - plug EVSE into a heavy duty, timer, 20A, and set it to run long enough to add the user indicated charge you want. @john1701a has already answered the absolute charge question and I'm in his camp.
    3. Smart EVSE - as an alternate to time, set the charge limit to a value that will give exactly the amount needed to achieve the user indicated charge.
    This will add a few extra steps when parking including the mental calculations. I'm not quite that OCD to worry about the indicated SOC except when I run an errand and have insufficient SOC to reach home. If needed, I'll extend my 'shopping' to make sure I can reach home in EV.

    As a reminder, also have a rag or tissue to wipe down the rear view camera lens. I just use my fingers and wash my hands when I get in. Fingers also work on curb sensors.

    Bob Wilson
     
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  12. Sam Spade

    Sam Spade Senior Member

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    It sounds to me like you somehow think that the power remaining in the battery at the end of the day will somehow be "lost".
    It won't.
    And when the battery meter says "full" it really is something around 80%.

    What you are wanting to do really would accomplish...........nothing useful.
     
  13. mr88cet

    mr88cet Senior Member

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    It's not a huge concern, but here's the scoop: I charge it home, at a price per mile about 80% that of gasoline, drive 19 miles to work, charge at work, then drive home. The charge at work uses the City of Austin's "all you can eat," so to speak, charging buffet: $50 per year to charge all you want around town. With the amount of charging I do, that probably works out to around 15% the cost per mile of gasoline.

    So, in concept, if I could charge at home only up to about 21 miles, and charge all the way full at work, I would consume a little bit less money on my Electric bill, and a little bit more on the City-subsidized program.

    I know the ChargePoint-branded home charger has such a feature. I needed a 24A charger though, so that it will fit on our 30A dryer circuit with the legally-required 20% margin, so I couldn't get that one.


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  14. mmmodem

    mmmodem Senior Taste Tester

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    So we're talking a kWh to work and a kWh from work savings. That's 2 kWh per day and at $0.10 - $0.20 kWh, you're looking at $50 to $100 savings a year.

    If it were me, I'd set the timer to finish about an hour later than when I actually leave in the morning.
     
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  15. bisco

    bisco cookie crumbler

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    great idea! might take a little experimentation to get it right, especially if you're not starting from the same charge % everyday.
     
  16. mr88cet

    mr88cet Senior Member

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    Yeah, like I say, it's not a big concern... More interested in increasing the charging margin at the top, fully-charged end.


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  17. Sam Spade

    Sam Spade Senior Member

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    So.....given the figures that you supplied,
    How about not changing at home AT ALL, given that the cost is about 80% of gas anyway ??

    That will use a little bit of gas each day and will help keep the fuel fresh.
     
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  18. john1701a

    john1701a Prius Guru

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    5 years (and 92,000 miles) of Prius PHV ownership makes this topic moot. I didn't do anything extra. Just plug & drive.
     
  19. mr88cet

    mr88cet Senior Member

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    Gas: Eeewww...

    :)

    I'll probably charge less at home in the future, by one means or another, but definitely keep driving on EV as much as possible. Quieter, cleaner, more responsive, etc.

    Last night for example, when I got home from work, I had 13ish miles left. Then my wife and I went to a mall that has charging available, so I plugged it in there. When we got home, the car had 21ish miles on it. I plugged it in more or less out of habit.

    In hindsight, I should have just not plugged it in, because 21 miles of charge should be fine to get me to work.


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  20. Sam Spade

    Sam Spade Senior Member

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    You actually CAN teach an old dog new tricks.
    The problem is getting him to UN-learn the old ones. :whistle:

    I know 'cause I are one. (y)