Charging at the top of a hill

Discussion in 'Prime Main Forum (2017-Current)' started by lllars, May 2, 2019.

  1. lllars

    lllars Junior Member

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    I live up a hill. Driving down the hill will charge the battery about 3% (regen). That becomes an issue when the car is already charged to 100%. About 2/3's of the way down the hill, the car decides it just can't squeeze any more juice into the battery, and kicks on the engine, presumably so it can engine brake instead of motor brake.

    Often, I'll be going somewhere entirely within EV range, so I'd prefer the engine stay off. The car should really have an option in the charging schedule to only charge partway. That would solve my problem, and also could be used to prolong battery life for anyone whose regular commute is significantly less than the EV range. But alas, no such option exists. So instead, I've come up with some workarounds. None are ideal, so I'm wondering if you guys have any other suggestions.

    Workaround #1: Schedule the charge to complete a few minutes later than I will actually leave. I've been playing around with this one, but it's not great. I've found I actually have to set it at least 55 minutes late for it to not be fully charged when I leave, and then the charge level is too variable. One day it might be 80%, the next 100%. Also, at 55 minutes late, I end up finishing my drive and plugging back in before the scheduled departure, so the car starts charging again right away rather than waiting for the next scheduled charge event.

    Workaround #2: Scheduled HVAC pre-conditioning. This seems like it should work to drain a bit of the battery just before departure. I haven't tested it yet, because the outside temperature is reasonable right now, so I'd actually have to set it to make the car uncomfortably hot or cold. It will probably be a good solution in the winter.

    Workaround #3: Driving down the hill in neutral. I tried this one this morning and it worked. It does seem like a shame to waste that potential regen energy and it puts extra wear on the brakes. I'm also wondering if this could harm the car in any way (the manual does say not to flat tow in neutral).

    So what do you guys think? Have any other ideas for me to try?
     
  2. sam spade 2

    sam spade 2 Senior Member

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    Work around #4:
    Try to get over your OCD.
    Don't worry about it.
    Seriously.
     
  3. jb in NE

    jb in NE Active Member

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    Other options - install a countdown timer to control your power outlet - something that would shut off power at 4 hours, for example. if you come home with less than 20% charge, this should stop the charge prior to a full battery. Easy enough to use - see how long the car is going to take to charge, then wind up the timer to 30 minutes less than that. Downside - can't do scheduled charge with this.

    Here is one example of such a device:

    From Clipboard.jpg

    Another option - get a smart wall outlet or plug that can be controlled from either a home hub or wifi. You would need to manually change the shut-off or start time each day or put a reminder on your phone to turn it on/off. I use the Samsung SmarthThings outlets, and these can be controlled via an app on the phone or via Alexa. So, if your phone timer goes off, tell Alexa to turn off the switch. Or, if using scheduled start, then adjust the on time to whenever it needs to be for a 90% charge.
     
  4. thefranchise713

    thefranchise713 Junior Member

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    Hmm, in my old traditional ICE car, coasting over 40 MPH would put the car into DFSO (deceleration fuel shut off) and shut down the injectors. Is the Prime going into a full engine warmup cycle going down hill? Or is it merely using the additional friction to slow the car, and never firing the injectors, potentially?
     
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  5. jb in NE

    jb in NE Active Member

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    Yes, but what the OP wants to do is to recapture that energy into the traction battery, which can only be done if the traction battery has sufficient remaining capacity to absorb the charge. If the battery is full, nothing can be stored.
     
  6. thefranchise713

    thefranchise713 Junior Member

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    You're right, sorry, I lost focus. For some reason my brain locked into "I'd prefer the engine stay off..." and went off the rails.

    Need more coffee, stat!
     
  7. lllars

    lllars Junior Member

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    I don't know if it fires the injectors or not, but it will keep the engine on for a good 10 minutes or so beyond the bottom of the hill. And it won't go back into EV mode during that time. So, yes to a full warmup cycle.
     
  8. bisco

    bisco cookie crumbler

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    if the top of the hill is where you charge up, just don't charge up all the way, as previously mentioned.

    if you leave the same time everyday, you can set the end timer for later than you leave. some experimentation will get you pretty close to perfect.
     
  9. lllars

    lllars Junior Member

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    I'm using a level 2 charger, so fancy outlet timers are a no go. But, the charger does have a phone app through which I can turn it off, and I can also program a schedule as to when the charger is working or not. I can also program the amount of current output available.

    Checking the remaining charge time and setting a phone timer is a good idea, and I might use that in the middle of the day. Kind of high maintenance though, so I could see getting lazy about it. For the morning drive, I'd rather let it do the scheduled charge as I think that will be better for the battery in the long run than letting it sit at 95% charged all night.

    Hmm... just thought of another potential workaround, lets call it #5: Always use "charge now" in the car, but program the L2 charger to only be "on" for a specific window of time. So for example, if the battery was fully drained and the charger window was 2 hours long, but the car would normally take 2 hours 10 min to fully charge. It's not perfect, as the amount of battery left at the end of the day varies between about 0 and 60%, and I don't want to be reprogramming the charger all the time, but an interesting option nonetheless.
     
  10. lllars

    lllars Junior Member

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    Tried that, doesn't work. See workaround #1 above.
     
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  11. bisco

    bisco cookie crumbler

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    missed that, sorry!:oops:
     
  12. Landon51

    Landon51 Member

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    Keep an eye on the coolant temp and your fuel per hour. If those don't change, you aren't consuming fuel. It keep the engine rotating for a few minutes just to burn excess banked power.

    Posted via the PriusChat mobile app.
     
  13. jb in NE

    jb in NE Active Member

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    Prime does not display coolant temp. Just a warning light.

    Tesla has this option - charge the battery to a variable level (set by the user), or go to full charge for maximum range. I think with the limited EV range of the Prime, there probably is very little demand for this (most users want to go max range).
     
    #13 jb in NE, May 2, 2019
    Last edited by a moderator: May 2, 2019
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  14. jerrymildred

    jerrymildred Senior Member

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    I don't live on a hill, but there are still times I don't want to charge all the way. The finish time is so inconsistent that I've never come up with a way to stop it accurately, even by manually unplugging it since we don't quite know how full the battery is without getting in and putting it in acc mode. Unless they decide to offer a Tesla-like "charge to X%" feature, I think we're stuck.
     
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  15. lllars

    lllars Junior Member

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    Ok, I've setup an experiment. I configured the L2 charger to only function between 4 and 8 AM with it's output limited to 6 amps. At 6A, it would take at least 4.375 hours to charge a full 6.3 kWh. So 4 hours should yield at most a 91% charge.

    My typical morning drive consumes ~40% charge. I scheduled the car (the car, not the L2) to start charging at 6:15 AM. So, it should charge for exactly 1.75 hours until the L2 charger stops it at 8AM, thereby charging the battery 40% (minus inefficiencies).

    The idea behind this scheme is that the 40% charge will happen automatically if I do nothing. If the battery is fully drained or I know I'll have extra errands to run the next morning, I can simply select "charge now" to get a 91% charge instead.

    I will report back with results as they come in. I'm sure the timing is going to need some tweaking. Also, the slow 6A charge rate is intentional, I figure it is gentler on the battery.
     
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  16. Roy2001

    Roy2001 Active Member

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    I am in similar situation. #3 works for sure. #1 won't work if the it is not warm enough and the hill is steep, ICE would still come.

    I tried to turn on heating and seats heater, rear defrost, that helps a bit, but ICE still come if it is cold.

    So my solution is to turn off the car and restart at the 1st stop sign after I get down from hill. But now as it is warm again, I no longer have this issue.
     
  17. noonm

    noonm Junior Member

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    Charger timer is probably your best bet. But if you really want to go down the project rabbit hole, how about this setup:

    Bluetooth OBD2 reader -> Raspberry Pi (to read the charge level)

    Raspberry Pi -> Relay or Power Switch (to turn off the charger when it reaches X% state of charge (SOC))

    I haven't done it myself, but it looks possible based on the following links:
    home automation - How can one control AC power (220V) with a Raspberry Pi? - Raspberry Pi Stack Exchange
    Everything You Need To Know To Integrate Your Raspberry Pi Into Your Car – Mahmoud Tantawy’s Blog
    Reading a car's OBDII port with a Raspberry Pi - Grappling with electronics

    I don't know whether you would need two Raspberry Pis (one in the car, one on the charger) or if just one would suffice.
     
  18. lextoy

    lextoy Active Member

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    does B mode instead of Neutral spin the ICE to "use the engine as a Brake" , thats why i recall it is for?
    if the ICE would kick on it would overrule the whole purpose of B mode, so maybe they built in a lock out to prevent ICE coming on in B mode?
    engine braking is specifically to slow the car without charging, so it might do what you need it to do ?
    i always used N on downhills to scrub the brake disks , every few months to. it doesnt add charge to the battery, but like you said, you are riding the brakes, not necessarily bad. they need to be polished since they get so little use.
    i tried B mode a few times , but it serves no purpose to me, i never needed to use the engine for braking, instead of using the transaxle charging function.
    i'm going from knowledge based on gen 2 B mode, and what i think i read about B mode in the prime. theres alot of B mode misconceptions out there. maybe i am off on my assumptions too.
    my thought is B mode acts purely to turn the ICE into an air compressor, closing valves but not firing , so the compression slows the revs.
    does it preclude ICE from firing? does it do anything to regulate transaxle resistance an thus charging?
     
  19. jb in NE

    jb in NE Active Member

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    In HV mode, yes. When in EV mode, B mode will increase the regenerative braking from the traction motor and recapture the energy to the battery.

    In this case, it is desired to capture the energy back into the battery, instead of dissipated as heat through spinning the ICE.

    B mode significantly increases regenerative braking in EV mode, and uses the ICE for braking in HV mode. In EV mode on a long downhill with sufficient capacity available in the traction battery to store the charge, a significant amount of charge can be put back into the traction battery. I put a few KWh into my battery in EV mode, B setting, going down I-70 grade off the Eisenhower tunnel in Colorado. That's about a 10 mile downhill. Put it in B, touched the throttle as needed to maintain speed on the flatter parts, never touched the brakes and the ICE never ran.
     
    #19 jb in NE, May 2, 2019
    Last edited: May 2, 2019
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  20. lextoy

    lextoy Active Member

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    start out in EV, get rolling, put it in B mode, foot off throttle, quickly hit the HV button to avoid excess regen...
    would that engage engine braking without starting the ICE?
    might not want to spin the ICE cold and dry, first thing every morning? i know it isnt really dry, but its not ideal condition to be pumping along for a few minutes cold every day. how long is this hill ?? how much regen can you capture if the battery isnt full ?
     
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