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[PROJECT] Lithium battery for Prius

Discussion in 'Gen 2 Prius Accessories & Modifications' started by Xeico, Feb 18, 2024.

  1. Xeico

    Xeico New Member

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    Hello everyone, since the fall of 2023 I have been developing a high-voltage battery for a Toyota Prius.
    Code:
    I am not a native English speaker, so sometimes I use a translator.
    I am in north California, you can meet me and see the prototype live.
    At the moment, I have already driven 8 thousand miles on the prototype of the first version.
    Everything works great for me, now I am in the process of finalizing and optimizing the appearance.

    My enthusiasm is fading a little, and I decided to start this blog to add information, maybe you will give me some new ideas.

    1. The goal of Prototype 1 was to make the high-voltage battery ECU work with lithium cells, a small device was developed to do this.
    2. In version 2, a device was developed with connectors, so that it could be connected to the HV Battery ECU without interfering with the car wiring. At any moment you could return to the original state.

    20240212_193800.jpg

    In version 3, the functionality is added to monitor the state of each cell by voltage, and when certain values are exceeded, an error is generated and displayed on the auto. (Also installation of additional temperature sensors.)
    In version 3 I encountered a large number of wires sticking out during installation and the board had to be redone from scratch..
    IMG20240121101045.jpg
    20240216_232809.jpg

    In addition, housings for the cells that are used in version 3 were developed.
    Different cells were tested.
    All cells used are high current, automotive grade.
    Version 1 uses 4.6 Ah cells.
    Version 3 will have 5.0 Ah cells
    Version 5 will have 5.5 Ah cells

    Now about fuel consumption.
    Test car Toyota Prius second generation 2005, with a mileage of 200 thousand miles.
    On average my consumption is 40 MPG.
    On the highway, it's about the same. If you drive with acceleration and 75 mph, it comes out to 37 MPG.
    I don’t like to drive economically; in a Camry hybrid I got 25 and 22 MPG, but now my wife drives consistently at 30 MPG.
    In any case, I started this project not to save fuel, but to forget about the existence of a high-voltage battery for a long time.


    Plans and what I want to implement:
    Version 3
    Complete testing of version 3 with as careful wiring as possible.
    Test the system in emergency situations

    Attention!
    Lithium cells are susceptible to fire and possible property damage and personal injury!
    I carry out all tests on my car in compliance with all safety rules.
    I strongly do not recommend performing tests and interventions on a high-voltage battery if you do not have the necessary skills and knowledge.
     
    #1 Xeico, Feb 18, 2024
    Last edited: Feb 18, 2024
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  2. Xeico

    Xeico New Member

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    I can immediately foresee a question.

    You can't just take and install a lithium battery from a new Prius! They are different in voltage, and increased voltage on the cells can lead to a fire!

    I cannot give a detailed answer to some questions, please treat this with understanding.
     
    #2 Xeico, Feb 18, 2024
    Last edited: Feb 19, 2024
  3. bisco

    bisco cookie crumbler

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    Sorry you’re losing enthusiasm, sounds like a great project!
     
  4. Xeico

    Xeico New Member

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    In any case, the project will continue, but if before I worked on it every day after work, now only on weekends and it’s hard to force myself
     
  5. bisco

    bisco cookie crumbler

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    I feel the same way about some projects
     
  6. Xeico

    Xeico New Member

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    Version 3 Installed in the car.
    Next week there will be full tests on long runs.

    PCB V4 has ben ordered.
     

    Attached Files:

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  7. Xeico

    Xeico New Member

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    Today I was stuck in a traffic jam for a bit, the speed on the highway was 70+ miles per hour, where the consumption dropped it was a traffic jam. It’s strange that in traffic jams my consumption is significantly lower than when driving on the highway.
    It's a pity that the Prius doesn't record the average speed.
    20240228_160453.jpg 20240228_164858.jpg

    I had an idea and decided to assemble a battery for a Prius 30. After assembly, I’ll try to find an enthusiast willing to test it. See how the battery behaves for a person who knows how to drive more or less economically.
     
    #7 Xeico, Feb 28, 2024
    Last edited: Feb 28, 2024
  8. Xeico

    Xeico New Member

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    The version 4 board arrived, everything works as planned, I connected to the computer. Next, I'll set up the configuration.
    bmb 4.png 20240302_181239.jpg
     
    #8 Xeico, Mar 2, 2024
    Last edited: Mar 2, 2024
  9. rewing

    rewing New Member

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    I'm curious as to why develop your own instead of just buying one that already exists ?
     
  10. Xeico

    Xeico New Member

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    The one that exists is not of very good quality, watch the video of disassembling the elements, what’s inside and how it’s assembled..
     
  11. rewing

    rewing New Member

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    That's a good reason. Part of my education is in Quality Control, so, I understand.
    Where is the video ? I don't see a video (or link to one) in this thread.

    FYI a local Japanese RHD Prius importer who I just bought my car from told me that the Toyota replacement battery is $4200 (CDN) and that the lithium battery he's been selling to people who want an upgrade is $3400 (CDN). It might be the one you're referring to - I don't know if there are others available.
     
  12. Xeico

    Xeico New Member

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    1st problem is soldering.
    In automotive design you CAN'T use soldering because of vibration.
    1soldering.png 2soldering.png
    2nd problem is balancing board
    It is based on cheap chinise chip. WITHOUT any safety featyre. For example, one cell is unsoldered. In this case, another cell will take on the entire load.
    3 Balancing board.png
    3rd and main problem is cells.
    Inside NexCell they use 5s2p circuit. The Prius Gen 2 the maximum discharge current that I have seen is 120A.
    Each cell with a capacity of 3.5 Ah must have a charge/discharge rating of 18C.
    I have not found cells with a similar characteristic in open sources.
    There is also a problem with the location of the cells; they lie close to each other, which indicates poor ventilation.
    In the new version they made holes at the bottom and top of the case, but in my opinion this will not help much.
    4 cells.png
     
    #12 Xeico, Mar 9, 2024
    Last edited: Mar 9, 2024
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  13. ChapmanF

    ChapmanF Senior Member

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    Toyota definitely uses non-solder connections (preferring proper crimps) in their wiring harnesses, where movement is expected. They definitely use solder on things like PCBs, where everything is rigidly held in place. The NexCell design seems sort of intermediate: definitely more motion possible than components all on one PCB, but less than in a wire harness; all the pieces seem pretty snugly secured there in that housing. What technique would you choose for joining those cells?

    Doesn't the video above show a 5s2p configuration (see at 10:52)? Is 9C a little more plausible?
     
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  14. Xeico

    Xeico New Member

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    1) Contact welding
    2) You're right it was a typo 5s2p. But anyway, I calculated right 120А / 2S/ 3.5АН = 17,2 ~ 18C
     
  15. Xeico

    Xeico New Member

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    Board version 4b has been developed.
    - The size of the PCB was reduced
    - Reduced number of connectors.

    Further plans include developing a case, board configuration, and installation in the car for testing.
     

    Attached Files:

    #15 Xeico, Mar 24, 2024
    Last edited: Mar 24, 2024
  16. TMR-JWAP

    TMR-JWAP Senior Member

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    I think I've documented 157(?) amps peak discharge on a full throttle acceleration from a stoplight.. I'll look around for the photo.

    This thread on a rebuilt battery I was testing:

    Just Another HV Battery Thread and Experiments | Page 2 | PriusChat

    172 amps discharge and 102 amps on regen, but I think I've hit higher numbers on regen previously..
     
  17. Xeico

    Xeico New Member

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    My lithium has no problem with high current.
    Also, I have some plans to test brand new cells from China. I already tested them with my equipment, but now I'm focused on the control board.
     

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  18. TMR-JWAP

    TMR-JWAP Senior Member

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    Didn't mean to imply anything about your battery. You had mentioned some current numbers in post #12 that you used in your calculation for determining C numbers. I just wanted to help you by providing some other real world max numbers I've seen while testing.
     
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  19. Xeico

    Xeico New Member

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    You indicate peak values; in general, I am more interested in current (A) values that last from 3 to 15 seconds. In any case, thanks for the information.
     
    #19 Xeico, Apr 1, 2024
    Last edited: Apr 1, 2024