Charging EV portion of the battery going down mountains

Discussion in 'Prime Technical Discussion' started by dalcon95, Feb 17, 2017.

  1. dalcon95

    dalcon95 Senior Member

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    I have a curious question. I haven't had an opportunity to try to go down some mountains to find this out, but how does the Prius Prime charge the EV portion of the battery going down mountains? Or does it do it at all? Or if it does, what conditions does it do it in? Does it need to be in charge mode? If it needs the charge mode, doesn't the gas being used be counter-productive in trying to regenerate power to the EV portion of the battery. So, who has some answers?

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  2. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    1) pressing the brakes gently charges the battery. (panic braking is via disc brakes)
    2) In a Prime, B mode may be the fastest way to charge.

    I am guessing you can recover 4000 vertical feet of energy. (no part of SC is over 3600 feet)
     
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  3. bisco

    bisco cookie crumbler

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    it charges the same way it charges whenever you're driving in any mode. the tranny motor generator is turned by the wheels, generating electricity to the battery. as long as your foot is off the gas or braking, it will keep charging until you are full, or the car reaches 6 mph and less.
     
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  4. dalcon95

    dalcon95 Senior Member

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    I know it is all one battery, but in hybrid mode with the EV portion of the battery being used solely for EV use is depleted, does the battery charge beyond the normal hybrid portion of the battery going downhill in the mountains? I use the mountains as an example for long duration for regenerating electricity to the EV portion of the battery.

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  5. dalcon95

    dalcon95 Senior Member

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    Ok. I wasn't sure if the hybrid system capped at the hybrid portion of the battery or if it would go beyond that to charge the whole battery. I know on a normal Prius when the battery is full, the regenerating has no place to go. Just curious if the plugin hybrid would allow it to charge the whole battery. Thanks for the info.

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  6. dalcon95

    dalcon95 Senior Member

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    Does B mode actually charge the battery faster or does it just use the engine as a brake so not to use the brakes as much? I know pressing the peddle generates electricity, but didn't know it was programmed to actually use the electric motor to slow the car down without hitting the brake peddle.

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  7. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    The answer is different for the PHV and Prime compared to non plug ins.

    A non plug in will fill the battery in less than 600 foot vertical drop so use the engine to slow the car.

    Your prime has a huge battery by comparison, perhaps a 4000 foot vertical drop to fill it. Those will be rare, so the engine as air pump is less of a strategy.
     
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  8. dalcon95

    dalcon95 Senior Member

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    Sounds like to me, if I want the most regenerating done in my Prime, I need to have it in D mode and use the brakes gradually and it will fill the whole battery eventually with a really long grade of mountain to go down on. If I am wrong, give me more info please.

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  9. EV-ish

    EV-ish Active Member

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    Forget about trying to optimize regen. The M/G just does not have enough of a efficiency power curve to dwell on. E.g,

    [​IMG]

    See how linear the red line is ?
    torque * rpm = power
    Keep the car at a nice safe speed and the rest will happen automatically.
    I find this aspect of electric motors to be one of the compelling features of EV driving: Whether driving at 10 kW or 60, uphill or down, the car's efficiency is not going to change much. All I have to do is watch the road and enjoy the ride.

    Earlier, I think you were asking if hybrid mode limits the regen energy the battery will take to some value below it's maximum capacity. The answer is no.
     
    #9 EV-ish, Feb 17, 2017
    Last edited: Feb 17, 2017
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  10. Insirt

    Insirt Junior Member

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    You're in SC so you've probably heard of Caesar's Head State Park. I drove up there one day and coming back down my battery was just depleted and I managed to charge up about 6 or 7 miles (out of a max of about 28 miles at the time) while braking (not in B, just in Drive) down an altitude change of about 1000 feet.

    It's a lot of fudging numbers, I'm not sure of the exact amount of charge I got or the exact altitude change down the steeper part of the mountain but for around 1000 feet you can say you'll get about 6 miles just using the brakes.
     
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  11. dalcon95

    dalcon95 Senior Member

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    That's nice to know. What I particularly had in mind was the drive through Cherokee NC to Gatlinburg TN. I was thinking of saving my EV range for going up the mountains and regenerating the most I can going down. That way I can drive around Gatlinburg and Pigeon Forge in EV mode with regenerated electricity.

    #1 in Easley,SC
     
  12. EV-ish

    EV-ish Active Member

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    Let's see.

    Regen is about 50% efficient
    Potential energy in Joules is mass*G*meters, so 1600*10*300 = 4.8 * 10^6 joules
    Half that is 2.4 * 10^6 Joules sent to the battery

    If we figure that a mile of flat driving consumes 220 Wh, that = 8*10^5 joules

    48/8 = 6 miles.

    Yep
     
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  13. bwilson4web

    bwilson4web i3 and Prime

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    I ran a quick sanity test descending a 525 ft, 8% hill at 65 mph. Initially everything looked pretty good until about 3/4th of the way down. It felt like the regeneration-charging slacked off and the car sped up. I plan to repeat the test recording a video and add instrumentation:
    • 55 mph - initial test to see if it was the rate that might have led to the early cut-out
    • 65 mph - replicate the original test
    Bob Wilson
     
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  14. dalcon95

    dalcon95 Senior Member

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    Do you have a YouTube channel for videos?

    #1 in Easley,SC
     
  15. bwilson4web

    bwilson4web i3 and Prime

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    No. I typically make the video and then manually retrieve the data into a spreadsheet for analysis.

    Bob Wilson
     
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  16. Tideland Prius

    Tideland Prius Moderator of the North
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    Basically, it's the opposite of what you were taught in a regular car. With the Prime, you do actually want to "ride" your brakes all the way down. I put ride in quotation marks because really you're using regen braking so your brake pads aren't being used. You want to max regen (or close to it) while maintaining your speed. That way, you can charge up the battery (and if you're in HV mode, it'll charge up past that and put you back into EV mode)
     
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  17. David Beale

    David Beale Senior Member

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    But remember, as in all Prius, you can only charge the battery to 80%. It will then stop regen. and use friction brakes. Of course 80% of the much larger battery in a Prime is a lot more than 80% of a standard Prius battery. ;) From the calculations done above in other posts, it appears you won't max. out the battery in SC.
     
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  18. dalcon95

    dalcon95 Senior Member

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    Of course when I mention regenerating electricity to fill the battery full, I know it only uses 80 % of the battery capacity each time it is charged "full". I am referring to the usable part of the battery. Apparently, there is a different strategy with the regular Prius versus the Prime because of the vast difference in battery size. I am needing to reprogram going from a 2005 Prius to a 2017 Prime in this regard.

    #1 in Easley,SC
     
  19. EV-ish

    EV-ish Active Member

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    OK then, an exercise:

    Say you want to finish at the bottom of your final descent of a trip with a full battery and you started the trip with a full battery. When do you change from EV to HV mode ? We'll presume for now that hills in the middle are not a consideration.

    It is actually a trivial question ;-)
     
  20. dalcon95

    dalcon95 Senior Member

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    Under the assumption that you would be driving more than the regenerated EV range, I would say put it in ECO HV mode until you get to stop and go traffic. On the other hand, like the example I mention above in Gatlinburg TN, if you go straight into the city from the descent of the mountain, I would just leave it in EV mode because I don't plan on leaving the city for the day.

    #1 in Easley,SC
     
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