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battery interchangeable?

Discussion in 'Gen 4 Prius Technical Discussion' started by mjoo, Nov 28, 2016.

  1. bisco

    bisco cookie crumbler

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    wow, i'd be done with that evil co.
     
  2. jdenenberg

    jdenenberg EE Professor

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    I'm running out of companies that I am willing to deal with.

    JeffD
     
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  3. bisco

    bisco cookie crumbler

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    sad, and getting sadder the next 4 years.
     
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  4. alanclarkeau

    alanclarkeau Senior Member

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    If you went back to the '60s when I started fiddling with cars, it was "possible" to put just about any engine+box in your car (I didn't, but witnessed a few). Diffs, wheels, carb jets etc were swapped. A/Cs (remember, they sat under the dash?) and Turbos were added. If you didn't have the part, you (or your welding shop) made up the mounting kit. Things like sets of points/plugs, distributors, carburetors were shared between brands of cars.

    Not any longer (unless you're BillTheEngineer!!).
     
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  5. bisco

    bisco cookie crumbler

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    when i was a lad, we walked both ways to school, uphill.:coffee:
     
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  6. alanclarkeau

    alanclarkeau Senior Member

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    ... or did it just feel that way? Me too - this was post-school I was talking about. Teenagedom.
     
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  7. bisco

    bisco cookie crumbler

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    feels that way more than ever. it's just not school anymore.
     
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  8. Trollbait

    Trollbait It's a D&D thing

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    Possible, but I suspect you have increased the cost for the pack.
    Mainly, having similar voltage outputs isn't enough. A basic lead acid battery charger can damage an AGM type battery, because it requires slightly different voltages during charging. There are far more differences between NiMH and Li-ion than in the variations of lead-acid. While I'm sure Toyota used hardware that can handle both battery types for charging duties, cars are not simply plug n' play like computer components.

    Still possible. Some have put a VW TDI into their Tacoma. It just now requires the knowledge of the control software. Simply upgrading the intake or exhaust requires tuning the ECM to actually get a performance change in a modern car; even with manufacturer parts.

    That increases the difficulty and cost in making such changes to a modern car, but there is a flip side to this. It is possible to change a car's performance, including improving fuel economy, simple by making changes to the software tune.:sneaky:
     
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  9. Prodigyplace

    Prodigyplace Senior Member

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    Open source software would provide more flexibility with a mountain of possible issues, some deadly.
     
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  10. mjoo

    mjoo Senior Member

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    The charger/discharger circuit is built into the battery pack. How do I know this? Each battery cell is either 1.2V (NiMH) or 3.7V (Li-ion) and you have up to 168 of these (see "Battery Specifications?" thread). You could charge these externally low voltage but for example the NiMH: for the same power output (P = V*I = V^2/R) it would take at least 28,056 times the current or 28,056 times the copper wiring to achieve this. Copper is expensive. Instead the drivetrain sends power to/from the battery pack using high-voltage lines. I would think that the high voltage is then stepped down to low voltage high current using lots of buck-converters. If I were designing this I would have short wires of low voltage to the battery's cells. This makes the battery pack economical to manufacture.

    Knowing Toyota, the inventor of LEAN manufacturing, if they could invent a common electrical interface for the Prius battery pack they would. The reason being they could develop a common wiring harness that can be used on all Prii of that generation. There are many advantages to using a common wiring harness including reduced cost: economies of scale in manufacturing, less time and money used to validate the harness, easier time finding errors in manufacturing, etc.
     
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  11. jdenenberg

    jdenenberg EE Professor

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    The solution is actually simpler and does not incur added costs.

    The State-Of-Charge (SOC) of the overall pack is communicated to the "Inverter" which by varying it's output voltage level determines the amount of current that is drawn from or sent to the HV battery depending on the needs of the vehicle and SOC of the battery. As long as both battery implementations have about the same voltage range and current handling capacities, they are then functionally interchangeable. Of course the reported SOC to the inverter would need to be normalized to account for the usable SOC range of each battery chemistry.

    JeffD
     
  12. Trollbait

    Trollbait It's a D&D thing

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    Which is likely in all the Prii ECU coding, but requires to be unlocked from outside.

    So swapping the NiMH and Li-ion packs on a Prius should be possible. The mounting hardware, and wire harness should be the same. Tuning the software will most likely need to be done in order for the ECU to know that the chemistry has been changed. From what I've seen for tune prices, that will likely cost $150 to $300 if you need to have someone else to do it. In the future, when a pack needs to be replaced, that might be worth upgrading to a Li-ion pack if the the cost vs NiMH has dropped enough.

    Getting an improved Li-ion, or even NiMH, chemistry pack likely isn't going to happen. Toyota wants you to buy a new car for it, so the gen5's pack likely won't be able to back-talk to a gen4 ECU. Most people will opt to pay less for the OEM chemistry when pack replacement is needed for an older Prius. So a third party pack isn't likely to appear, and then those that happen to do so might be like 3rd party batteries for Panasonic cameras, and simply not work because of the proprietary nature of the control software.
     
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  13. bisco

    bisco cookie crumbler

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    if you're leaving the main road, you had better be prepared with emergency supplies.
     
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  14. goku2

    goku2 Junior Member

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    In all honesty folks, I would not be surprised if putting the Lithium Ion pack is a drop in install. The whole "ecu tuning" and whatnot is stupid and irrelevant. The voltages don't matter, nothing matters because they wouldn't design the prius with that significant of a difference between a single trim of vehicle and all the other vehicles they make. If you understand how battery packs work, it's like the difference with laptop computers (20 years ago) accepting a Lithium Ion battery or NIMH battery. The car/computer is communicating with another computer inside the battery pack and that battery pack computer handles all of that stuff. As long as the interface is the same between the car and the battery pack, it should be a drop in install. It would save no money or time having a different ECU for a Prius with a Lithium pack and a NIMH pack. In fact, I doubt there is any necessary additional programming for the ECU required as the battery pack ECU is what handles all the charging/discharging algorithms.


    The much harder question is how can you justify going with a Prius II when for $800 more, you can get a better trim with a Lithium Ion battery pack. Hard to get a salvage battery for $800 and you're still missing out on the other features that higher trims have.
     
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  15. Prodigyplace

    Prodigyplace Senior Member

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    Moving from Two to Eco is a step down for many. You lose the spare tire, rear wiper and now the cargo cover.
    The trim Three is s much larger price difference.
     
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  16. mjoo

    mjoo Senior Member

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    I agree. There's already a battery ECU in the pack that should act as a common interface with the main ECU. Thanks for expounding on this.

    The only conflict I can see is if there's programming in the ECU that prohibits using other packs.
     
    #36 mjoo, Oct 10, 2017
    Last edited: Oct 10, 2017
  17. Prodigyplace

    Prodigyplace Senior Member

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    The PiP ECU should work then, I expect. They have a Li-Ion battery pack.
     
  18. mjoo

    mjoo Senior Member

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    Suppose that in 5 years from now all lower trim modules use Li-ion and all NiMH battery packs aren't produced. Also suppose that in 10 years from now the traction battery dies on a Gen 3 Prius or a Gen 4 Prius trim 2 and I wish to continue with this car. In 10 years the Li-ion pack may be cheaper and easier to acquire than a NiMH and may have more life.

    Why think this far ahead? I'm curious how the system works.
     
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  19. bisco

    bisco cookie crumbler

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    but you can't put li-on in gen 3.
     
  20. bisco

    bisco cookie crumbler

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    the computer handling of ev batteries is way more complicated than laptops.
     
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