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Adding 2nd Lithium pack in Parallel

Discussion in 'Gen 4 Prius Technical Discussion' started by Brandon Kennedy, Feb 28, 2022.

  1. royrose

    royrose Senior Member

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    I was focused on whether fuel economy would be improved, not on acceleration. However, I don't see how it would increase acceleration since the software that controls the hybrid system wouldn't change and currently, to my knowledge, acceleration is not affected by how much charge the battery has. When the battery is nearly depleted, the ICE revs more to send some more power to the electrical system to maintain torque/power.

    I live in Colorado with long uphill drives in the mountains, including a 14 mile, 2,000 ft elevation gain near my home, and never felt a loss of acceleration. So I don't expect that adding battery would change that.
     
    #41 royrose, Oct 14, 2022
    Last edited: Oct 14, 2022
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  2. nik2208

    nik2208 New Member

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    this is an interesting study about the topic.. it seems to give positive answer to both the questions "is it possible" and "is it worth"
     

    Attached Files:

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  3. nik2208

    nik2208 New Member

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    just added to this thread a relevant study about the topic, hope u'll take notice of that. You're right along all the line.
     
  4. bisco

    bisco cookie crumbler

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    interesting study, but i couldn't find the answer to 'is it worth it', or any cost involved
     
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  5. vvillovv

    vvillovv Senior Member

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    Ask @jacktheripper if he thinks it's worth it.

    It's a complex system that is only getting more complex as battery technology advances.
    It's expensive to add another pack to a car and the benefits are not completely doubled as most might believe at first when pondering the issues.
    If you can DIY than it can easily pay for itself within the lifetime of the car, but there are a lot of reasons for that not necessarily related to the extra battery pack itself.
     
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  6. Loc Tran

    Loc Tran New Member

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    I just paid off my Prius Prime and thinking I want to do something like this to get more miles on EV and also learn about batteries. I'm thinking that the Prime has 5 batteries in series and perhaps instead of 2nd pack in parallel with the 1st pack, how about 5 smaller parallel packs in series?

    I'm thinking this is what I would do...
    1. Add BMS to monitor each cell
    2. Build embedded controller that monitors each cell BMS and basically spoof the BMS signals
    3. Each of the parallel packs to have relays to disconnect in case of cell failure, balance issue or short, etc...
     
  7. Michael Cyr

    Michael Cyr Junior Member

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    I know this is an older thread but I'm thinking about doing the same thing because I have a spare pack in the garage right now. Here's what I see happening in a parallel situation.

    1. because the two packs are not at exactly the same voltage and internal resistance, one of them will end up slowly trying to charge the other one when the car is off.
    2. To avoid this I'm thinking of rigging up the factory relays of the second pack to disconnect it from the primary pack when the car is off.
    3. When the car is on, the battery ECU is going to only be able to monitor the voltages of the 14 blocks in the primary battery.
    4. Having the second battery in parallel will effectively double the AH capacity and hence theoretically it should charge twice as slowly as when there is only one battery pack.
    5. The slower charging MIGHT make the battery ECU conclude that there's something wrong with the primary battery, but I'm guessing not. It won't be able to monitor the individual block voltages so what it'll see if the primary battery's block voltages and the TOTAL voltage of the two packs.
    6. My guess is that it will work fine and any issues would simply show up as codes and not cause any damage. (but don't blame me if it does).
    7. the second battery will need a cooling fan hooked up and probably just wired to run all the time.
    8. I would wire in the second pack so that it get's disconnected by the relays in the primary pack. you won't want the inverter energized with 200vdc when the car is off. You could even wire the second pack (after its own internal relays) to the first and last post of the primary battery.
    9. The second battery is going to weigh about 100lbs and needs to be bolted down somewhere do it doesn't become a missile in an accident.

    Let me know if you tried it and how it worked. Very curious.

    Mike in Maine
    2005, 2005, 2005 Priuses

     
  8. bisco

    bisco cookie crumbler

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    many people have thought about doing this. why they don't follow through is beyond me
     
  9. rjparker

    rjparker Tu Humilde Sirviente

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    Because if they did it failed. Assuming they did not get stopped by the laws of physics, they risked serious electrical flash burns.

    Laws of Physics Kansas City.jpeg


    Reverse engineering and then rewriting Toyota's code is a possibility but if they could do that they could afford a Tesla Model S Plaid.

    IMG_0315.jpeg
     
    #49 rjparker, Aug 20, 2023
    Last edited: Aug 20, 2023
  10. sam spade 2

    sam spade 2 Senior Member

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    Have you also considered what might happen if one cell group in one of the packs goes shorted or reversed......
    And the other healthy pack tried to overcome that ??

    High capacity batteries in parallel is a tricky proposition.
    Especially when the chemistry involved is known for catching fire
    under "normal" use.
     
  11. black_jmyntrn

    black_jmyntrn Senior Member

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  12. GoodOldBob

    GoodOldBob Junior Member

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    Well, I do know that the Prius Prime isn't "just a Prius on steroids" and has been totally redesigned and tweaked from the bottom up. The Transaxle has different gear ratios, the battery has a higher voltage and I'm sure the charge/discharge profile has been changed along with all the power handling circuitry. The Prime is a whole new ballgame.
    looks at the Transaxle in extreme detail (2 hours) and talks about the gearing differences. He also, in subsequent videos, talks about the circuit differences.
     
  13. black_jmyntrn

    black_jmyntrn Senior Member

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    did you know... the Gen5 Prius and Rav4 Prime share the same CVT? That would mean, swapping the 2.5L Rav4 Motor into a Gen 5 Prius would be easier than me swapping the 2.0L into my 2013 PIP and using the PriusCVT!

    I'm really curious about the max speed limit the new Prius Prime has while driving in EV mode. my PIP if not mistaken to 25mph... Gen 4 PrimePrius up to 80mph and that was discussed in a thread I started as the clutch plate the newPrime is what enable 80mph plus ECU.. I am working to get my hands on one to takes steps in replecating this in my PIP...

    That said, when you think about the Rav4 Prime being quicker than the new supra...i was excited about the upgrade possibilitys in the new Prius but... from what Im hearing no more CAN as Toyota encryted the can bus interface
     
  14. rjparker

    rjparker Tu Humilde Sirviente

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    Thought that was all figured out
     
  15. black_jmyntrn

    black_jmyntrn Senior Member

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    in what regard? the rumors I've heard seem to indicate the new technology toyo stuff is just like the legacy and the people claiming its encrypted have only mentioned needing the codes to program keys just like our generation now. but... after talking to a company that makes a sort of tuner for the GR Corolla it's my belief there is possibly some truth to the whole being encrypted yet I haven't been able to connect my tools/hardware to a newer Gen Vehicle to know for certain.
     
  16. GoodOldBob

    GoodOldBob Junior Member

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    Perhaps that is why I can't get my Chinese OBD2-to-Bluetooth dongle to talk to my 2020 Prius L Eco OBD2 port although the dongle pairs OK with my cellphone? I can't get Dr.Prius or TorquePro to work with the Dongle at all. Perhaps the fault lies in an encrypted OBD2 port instead.
     
  17. black_jmyntrn

    black_jmyntrn Senior Member

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    oh no good sir, thats because cheaper Chinese OBD2 Device.
    This link has a video that explains why a Prius needs a higher-quality device.
    DO NOT BUY A LOW COST OBD2 DONGLE FOR YOUR PRIUS

    My advice is get the MX+
    NEW OBD2 BLUETOOTH ADAPTER IS BETTER THAN CARISTA
    One thing to note, you never have to pay a membership or pay for any additional software or access with the MX+.

    Even the connection speed/quality is unmatched after testing a good 10+ OBD2 Devices.
     
  18. tekstyle

    tekstyle Junior Member

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    I think it will work. the electronics don't know they're is a second pack in parallel. it will take longer to charge and longer to drain. if 80% of 1 pack equates to fully charged, then 80% of both will equate to full. the bms will balance, and control over charge and under discharge (assuming the bms is a closed system). I think this it's only worth while in a plug-in with EV mode. the car will monitor voltage drop to determine if it's going to switch to hybrid mode. I don't see the point in a Prius without EV mode
     
  19. tekstyle

    tekstyle Junior Member

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    now. besides messing with the cars electronic, I have been worrying if it's possible to charge the plug in through the 1772 port while the car is moving. that would be a simpler solution. so it needs is a power station in the trunk and the charge cable
     
  20. bisco

    bisco cookie crumbler

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    how could you charge and discharge at the same time?